7 The Physics Science Orbit - SARASWATI HOUSE Material... · 2018. 7. 3. · 7. Density is mass per...

7

Teacher’s ManualScience OrbitThe Physics

Kishwar Raza

(An imprint of New Saraswati House (India) Pvt. Ltd.)New Delhi-110002 (INDIA)

R

(An imprint of New Saraswati House (India) Pvt. Ltd.)

R

Second Floor, MGM Tower, 19 Ansari Road, Daryaganj, New Delhi-110002 (India) Phone : +91-11-43556600Fax : +91-11-43556688E-mail : [email protected] : www.saraswatihouse.comCIN : U22110DL2013PTC262320Import-Export Licence No. 0513086293

Branches:

• Ahmedabad (079) 22160722 • Bengaluru (080) 26619880, 26676396 • Bhopal +91-7554003654 • Chennai (044) 28416531 • Dehradun 09837452852• Guwahati (0361) 2457198 • Hyderabad (040) 42615566 • Jaipur (0141) 4006022 • Jalandhar (0181) 4642600, 4643600 • Kochi (0484) 4033369 • Kolkata (033) 40042314 • Lucknow (0522) 4062517 • Mumbai (022) 28737050, 28737090 • Nagpur +91-7066149006 • Patna (0612) 2275403 • Ranchi (0651) 2244654

First published 2018

TM Code: 2017007000111

Published by: New Saraswati House (India) Pvt. Ltd.19 Ansari Road, Daryaganj, New Delhi-110002 (India)

The moral rights of the author has been asserted.

©Reserved with the Publishers

Publisher’s Warranty: The Publisher warrants the customer for a period of 1 year from the date of purchase of the Book against any Printing/Binding defect or theft/loss of the book. Terms and Conditions apply: For further details, please visit our website www.saraswatihouse.com or call us at our Customer Care (toll free) No.: +91-1800-2701-460Jurisdiction: All disputes with respect to this publication shall be subject to the jurisdiction of the Courts, Tribunals and Forums of New Delhi, India Only.

All rights reserved under the Copyright Act. No part of this publication may be reproduced, transcribed, transmitted, stored in a retrieval system or translated into any language or computer, in any form or by any means, electronic, mechanical, magnetic, optical, chemical, manual, photocopy or otherwise without the prior permission of the copyright owner. Any person who does any unauthorised act in relation to this publication may be liable to criminal prosecution and civil claims for damages.

Printed at: Vikas Publishing House Pvt. Ltd., Sahibabad (Uttar Pradesh)

Product Code: NSS2TSO076PHYAA17ICN

This book is meant for educational and learning purposes. The author(s) of the book has/have taken all reasonable care to ensure that the contents of the book do not violate any copyright or other intellectual property rights of any person in any manner whatsoever. In the event the author(s) has/have been unable to track any source and if any copyright has been inadvertently infringed, please notify the publisher in writing for any corrective action.

The purpose of The Science Orbit series (3 to 8) teacher’s resource pack is to empower teachers to make classroom teaching a holistic experience. It will enable teachers to explain the chapters in the most effective way, which will not only impart knowledge, but also ignite interest in the minds of young learners towards the subject. A wide array of resources complement these manuals, which makes learning an interesting process instead of a routine chore.

Teacher’s Manual

Teacher’s Manual resources have been carefully prepared with an aim to make the process of teaching and learning interesting and intriguing for the teachers and learners alike. It comprises detailed lesson plans and answers to the coursebook along with solved worksheets and model test papers. These have been prepared keeping in mind the explanation of the concepts and the level appropriateness of the topics. Easily available teaching aids are used to make teaching and learning an interactive and lucid process. The lesson plans give a topic-wise explanation of each chapter. Its components are:

– Warm-up section guides the teacher to start the topic in an interesting way.

– Learning objectives give the list of measurable aims of each chapter, which should be achieved after teaching the chapter.

– Concept explanation gives a detailed method of explaining the important concepts of the chapter using various teaching aids.

– Reinforce section allows the teacher to check the progress of the concepts learned by the students with the help of textual questions and worksheets and allows them to revisit and revise the concepts, if required.

– Explore section helps the learners to do various activities, often taking them beyond their classroom learning.

App-based Digital Store

Digital offerings comprise digital resource embedded e-book, 2D and 3D animations, videos, interactive activities, slideshows, educational games, test generator and teacher’s manual.

Web Support

The web support consists of worksheets, model test papers, and answers to worksheets and model test papers. These would help teachers in assessing students on the concepts taught in the class.

Preface

Contents

1. Physical Quantities and Measurement 5

2. Force and Pressure: Motion 12

3. Energy 19

4. Light Energy 26

Model Test Paper 1 35

5. Heat 37

6. Sound 45

7. Electricity and Magnetism 53

Model Test Paper 2 63

55

Learning Objectives

Students will be able to: learn the concept of measurement of volume, measurement of area

understand the concept of measurement of density

understand the concept of speed, uniform and non-uniform, with examples.

1 Physical Quantities and Measurement

Warm-upAsk the students whether life would be possible without measurement. Explain to them the necessity of measurement to carry out daily life activities. Give example of measuring the volume of the container in which milk or water is poured. Explain fi nding the volume of a matchbox which is an example of a cuboid. Pick up two or three different leaves of different shapes and fi nd the area by placing each leaf on a graph paper.

Read the Warm-up section from the book and do the activity given in this section.

Concept Explanation

Measurement of Area, Measurement of Volume– Students are shown sugar cubes, match-

box, shoe-box, cutouts of circles, triangles and squares to explain the concept and calculation of area and volume.

– Read the related sections from the textbook.

– Conduct the activity and experiment given on page 11 for better understanding of the concept.

– Conduct the activity given on pages13 for better understanding of the concept of fi nding area of irregular shapes.

– To reinforce ask the students to do the Pause and Do section given on page 13 in the textbook.

– Ask the students to answer the related questions from the Part II of the Exercises.

Measurement of Density– Place a 100 g weight each of cotton and

iron on either arm of a physical balance.

– Read the related section from the textbook.

– Explain that for the same mass of iron and cotton, cotton has greater volume and hence less density.

– Conduct the activity given on page 14 for better understanding of the concept of comparing the masses of two substances with equal volumes.

– Use examples given in the related section to make them understand the concept in an easy way.

– To reinforce ask the students to do the Pause and Do section given on page 15 in the textbook.

66

– Ask the students to answer the related questions from the Part II of the Exercise.

Speed– Read the related section from the

textbook.

– Write the relation among speed, distance and time on the blackboard.

– Defi ne the terms distance, time and speed to the students.

– Explain that the distance covered by a body in unit time is called the speed of the body.

– Differentiate between uniform and non-uniform speed of an object.

– With the help of examples of motion in everyday life, explain the uniform and

non-uniform speed.

– Write formulae on the blackboard on area, volume, density and speed and numericals for more practice.

– Ask the students to answer the related questions from the Part II of the Exercise.

ReinforceTo reinforce, read the Summary and Glossary sections from the book. Ask the students to do Pause and Do section from the book. Use Part I of the Exercises to conduct a quiz in the class.

ExploreTo explore, ask the students to do the Learning Zone section from the book.

77

Worksheet 1

1. Fill in the blanks.

a. A match box is an example of a _____________.

b. Liquids such as water and alcohol form a _____________ meniscus.

c. _____________ and _____________ are smaller units of area.

d. Among the two, 100 g of iron and 100 g of cotton, _____________ has greater volume.

2. State True and False.

a. Volume of a cube is l × b × h

b. Volume of an irregular solid is measured using a graph paper.

c. When a body covers equal distance in equal intervals of time it is called uniform speed.

d. Larger areas like fi elds are measured in acres and hectares.

3. Choose the correct alternative.

a. SI unit of density is,

i. g/cm3 ii. kg/m3 iii. g/m3 iv. kg/cm3

b. Volume of an irregular solid is measured using a

i. measuring jar ii. tumbler measure

iii. test tube iv. burette

4. Answer the following questions.

a. Explain how you will fi nd the area of an irregular surface?

_____________________________________________________________________

_____________________________________________________________________

b. A cycle rickshaw carries you to school in half an hour. The distance of your school from home is 6 km. Calculate the speed of the rickshaw.

_____________________________________________________________________

_____________________________________________________________________

88

Worksheet 2

1. Circle the odd one out.

a. m3, litre, mL, km, cm3

b. speed, velocity, density, acceleration

c. pipette, burette, bucket, measuring jar, tumbler measure

d. cube, square, cuboid, stone, metal sphere, metal pipe

2. Match the following.

a. Speed i. Square metre

b. Density ii. Litre

c. Volume iii. kg/m3

d. Area iv. km/h


a. How is the volume of liquids measured?

_____________________________________________________________________

_____________________________________________________________________

_____________________________________________________________________

b. Name some bigger units of area. What does each one of them measure?

_____________________________________________________________________

_____________________________________________________________________

_____________________________________________________________________

c. The area of a rectangular garden is 320 square metres. If the length of the garden is 25 m, fi nd its breadth.

_____________________________________________________________________

_____________________________________________________________________

_____________________________________________________________________

_____________________________________________________________________

99

Answers to Coursebook

PART 1

A 1. (d) 2. (d) 3. (b) 4. (d)

5. (a) 6. (c) 7. (b) 8. (b)

B. 1. Volume 2. capacity

3. pipette 4. upwards

5. area 6. square metre

7. graph paper 8. more

9. density

C 1. F 2. T 3. F 4. T

5. F 6. F 7. F 8. F

D. 1. (e) 2. (c) 3. (d) 4. (a)

5. (b)

PART 2

A. 1. Volume is the amount of space occupied by a substance.

2. SI unit of volume is m3.

3. Decimetre cube (dm3) and centimetre cube (cm3)

4. Pipettes and burettes

5. m2

6. 1 hectare = 100 acre

7. Density is mass per unit volume of a substance.

B 1. Speed is the distance covered by a body in unit time.

Speed can be uniform and non-uniform.

2. Volume of a cube = side × side × side or (l3) (Where, l = side of the cube)

Volume of a cuboid= l × b × h (Where, l = length, b = breadth, h = height)

3. Area of a square= (side)2 or a2 (Where, a = side of the square)

Area of a rectangle = l x b (Where, l = length, b = breadth)

4. Area of an irregular shape can be calculated by placing the shape on a graph paper and counting the number of squares enclosed within it.

5. Density of a solid can be calculated using the formulae,

6. km/h

C 1. Pipette and burette (Refer Fig. 1.1 from the textbook).

2. Fill water in a measuring jar till the mark 30 mL. Gradually suspend the stone in water and note the fi nal volume of water. The reading shows 37mL. The difference between the fi nal and initial volume gives the volume of the stone in cm3. Here volume of The stone is 7 cm3.

3. a. Area of a rectangle= l x b, Square feet or m2

b. Square feet

c. Square km

d. Acre or hectare

4. Density is mass per unit volume

Density is directly proportional to mass, and inversely proportional to volume.

5. 50 gm of cotton has more volume, it occupies more space per gram.

D 1. Volume: The amount of space occupied by a substance is called its volume. Volume

Of liquids can be measured by the volume of its container.SI unit of volume is m3.

2. Area: Amount of surface covered by a closed shape is called area. Area of regular Shapes can be measured by using a known formulae. Area of irregular shape is Measured by using a graph paper. SI unit of area is m2.

3. Density : Density is mass per unit volume. When the particles of a medium are closely Packed together, its density will be

1010

more than when the particles are far apart. For example, solids are more dense than liquids and gases. SI unit of density is kg/m3.

Speed: Distance covered in unit time. Speed can be uniform and non-uniform. SI unit of speed is m/s.

E 1. Area: Amount of surface covered by a closed shape is called area. Area of regular shapes can be measured by using a known formulae. Area of irregular shape is measured by using a graph paper. SI unit of area is m2.

Volume: The amount of space occupied by a substance is called its volume. Volume of liquids can be measured by the volume of its container. SI unit of volume is m3.

2. Volume: The amount of space occupied by a substance is called its volume.

Capacity: Volume of liquids can be measured by the volume of its container. The inner volume of a container is called its capacity.

3. Concave meniscus: Liquids like water, alcohol when poured in a measuring jar or any container curve downwards, called concave meniscus.

Convex meniscus: Liquids like mercury when poured in a container curve upwards, called convex meniscus.

F 1. Volume of a cuboid: l × b × h

= 20 cm × 15 cm × 10 cm = 3000 cm3

2. Area of the fl oor = l × b

132 m² = 12 m × b

b = 11 m

3. Area = l × b

117 m² = l × 9 m l = 13 m

4. Speed = DistanceTime

⇒ s = 5490 × 60 =36 km/h

5. 15 min = 15 × 60 seconds = 900 seconds

Distance = speed x time

= 2 × 900 = 1800 m or 1.8 km

6. Density in SI unit

= 7.9 × 1000 = 7900 kg/m3

7. D = MV ⇒ V = Md = 3127.8 = 40 cm3

8. Mass = V × d, = 25 × 0.25 = 6.25 g

LEARNING ZONE

Picture based questions

1. Train ‘a’ is faster

2. a. 7 cm3

b. 15 cm3

c. Stone in jar c.

d. 8 cm3

3. a. Mark concave and convex meniscus

b. Water

c. Mercury

Think and answer

1. Cube: 11 cm × 11 cm × 11 cm = 1331 cm3

Cuboid: 11 cm × 12 cm × 8 cm = 1056 cm³,

The cube has more volume

2. Making the outline of the foot on paper and then placing it on graph paper.

Answers to Worksheets

WORKSHEET 1

1 a. cuboid b. concave

c. dm2 and cm2 d. cotton

2. a. False b. False c. True

d. True

3. a. ii b. i

1111

4. a. Area of an irregular surface can be measured by fi rst placing it on a graph paper. The Number of complete 1cm squares and half and more than half squares are counted.

This number gives the area of the irregular shape directly.

b Speed = distance / time, i.e.,

Speed = 61/2 km/h = 12 km/h

WORKSHEET 2

1. a. km b. density c. bucket

d. square

2. a. iv b. iii c. ii d. i

3. a. Liquids such as water, milk and petrol are stored in containers. These containers have a fi xed capacity and come in different shapes and sizes. A few of these are measuring jar, 500 mL

and 250 mL containers generally used by milkmen.

250 mL500 mL

b. Bigger units of area are acre, hectare and square kilometer. Acre and hectare are used to measure large fi elds and districts. Square km is used to measure plot of land.

c. b = Al = 32025 = 12.8 m

1212

Learning Objectives

Students will be able to: learn about various types of motion and its types

understand the concept of scalar and vector quantities

defi ne and differentiate between distance and displacement

learn about uniform and non-uniform motion

understand the concept of average speed, mass and weight, and accelerationdue to gravity

2 Force and Pressure: Motion

Warm-upTake the students to a zoo or a park for an excursion. Ask them about objects in motion. Show them running deer, birds fl ying, cars moving on the road, etc. Explain to them objects that are at rest and those that are in motion with respect to some other objects. The driver of the car is in motion with respect to us, when we are standing on the road.

Explanation of various types of motion exhibited by objects round us can be given.

Read the Warm-up section from the book and do the activity given in this section.

Concept Explanation

Motion, Types of Motion– Roll a ball down the ground; ask a boy

to run in a circle; show the children the blades of a moving fan; ask them to observe wheels of a moving car, children playing on a swing and birds fl ying in the sky. Ask them to list the various types of motion seen by them.

– Classify these motions as translatory, rotatory, oscillatory, periodic, non-periodic and multiple motion.


– To reinforce ask the students to do the Pause and Do section given on page 25.

– Ask the students to answer the related questions from Part II of the Exercises.

Scalar and Vector Quantities– Physical quantities such as mass, time,

length, distance, displacement, density, temperature, velocity, area, speed, acceleration, volume, etc., can be written on the blackboard.

– Ask students to separate them into two groups, such as those that show only magnitude and those that represent both magnitude and direction. Thus the concept of scalar and vector quantities can be explained to the students.

– Distance and displacement can be explained by throwing a ball up and

1313

letting it come down to the same position on the ground. Thus displacement can be shown to be zero but distance can never be zero.


– To reinforce, ask the students to do the Pause and Do section given on page 27.


Uniform and Non-uniform Speed; Average Speed; Weight– Uniform motion can be explained by

using a remote control toy car and setting it in motion such that it moves equal distance in equal intervals of time, or giving the example of motion of planets around the Sun. On the other hand non-uniform motion can be the motion of any vehicle on the road.

– Give examples of raindrops falling, or fruit falling on the ground, people moving about comfortably on the earth as against that on the moon. Develop the concept of gravitational pull of the earth.

– In the science lab of the school, students

can be shown a spring balance and a physical balance and objects can be weighed to explain the difference between mass and weight.

– Explain that the average speed is calculated by fi nding the ratio of the total distance travelled by the body to the total time taken for the journey


– Use the table to differentiate between mass and weight.

– Conduct the activity given on page 29 for better understanding of the concept.

– Ask the students to answer the related questions in Part II of the Exercises.

ReinforceTo reinforce, read the Summary and Glossary sections from the book. Use Part I of the Exercises to conduct a quiz contest in the class.


1414

Worksheet 1


a. The objects which change their position with respect to time are said to be in ______________.

b. ______________ motion is repetitive and fl uctuates between two locations.

c. Displacement is a ______________ quantity.

d. The gravitational pull on an object ______________ as its distance increases from the surface of the earth.

2. State the type of motion in the following.

a. A bee moving from fl ower to fl ower. ______________

b. A ball struck hard by a batsman. ______________

c. Playing on the strings of a guitar. ______________

d. A drill machine. ______________


a. Give the difference between distance and displacement with an example for each.

_____________________________________________________________________

_____________________________________________________________________

_____________________________________________________________________

b. How is vibratory motion different from rotatory motion? Explain with an example.

_____________________________________________________________________

_____________________________________________________________________

_____________________________________________________________________

c. Calculate the speed of a cyclist moving 5 km in 40 minutes.

_____________________________________________________________________

_____________________________________________________________________

_____________________________________________________________________

1515

Worksheet 2

1. Choose the correct answer.

a. When a body moves unequal distances in equal intervals of time, the motion is said to be

i. average speed ii. uniform speed

iii. non-uniform speed iv. uniform velocity

b. Force of gravity is directly proportional to the

i. mass of the body ii. weight of the body

iii. motion of the body iv. none of these

2. State true or false.

a. A spring balance measures weight in Newton.

b. Motion that changes its direction continuously is called random motion.


a. Motion of a grasshopper i. Rotatory and translatory

b. Motion of electrons around the nucleus ii. Random and non-periodic

c. Motion of the bob of a pendulum iii. Rotatory and curvilinear

d. Moving wheel of a car iv. Oscillatory or vibratory


a. What is acceleration due to gravity? How does it vary from place to place?

_____________________________________________________________________

_____________________________________________________________________

b. Calculate the distance covered by a boy going to school on a bicycle at a speed of 13 km/h in half an hour.

_____________________________________________________________________

_____________________________________________________________________

_____________________________________________________________________

1616


PART 1

A 1. (d) 2. (d) 3. (d) 4. (b)

5. (d) 6. (a) 7. (a)

B 1. curvilinear 2. oscillatory

3. periodic 4. random

5. scalar 6. vector

7. uniform

C 1. True 2. True 3. False

4. True 5. False 6. False

7. False 8. False 9. False

D. 1. Oscillatory 2. Vector

3. Rectilinear 4. Spring balance

5. Newton 6. Distance

7. Displacement

PART 2

A 1. Rectilinear motion

2. When an object moves equal distances in equal intervals of time, the motion is uniform.

3. Motion of a pendulum is oscillatory

4. Motion of the blades of a fan

5. Vibratory motion

6. Periodic and rotatory

7. Displacement shows direction also, hence it is vector.

8. Mass, temperature

9. W = mg

B 1. To and fro motion is called vibratory motion. It can be the string of a guitar or plucking a stretched rubber band. Even ripples formed in water are vibratory.

2. Motion of objects in a straight line is called rectilinear motion. For example, a car moving on a straight road.

3. Translatory, rotatory and vibratory motion.

4. Weight: It is the force with which the Earth attracts a body towards it.

Mass: It is the amount of matter contained in a body.

5. The motion of the hands of a clock is circulatory or rotatory.

6. A bee moving from fl ower to fl ower, children playing in a park, birds fl ying in the sky.

7. Quantities that show magnitude as well as direction are called vector quantities. For example, displacement, velocity, weight, etc.

C. 1. Objects which do not change their position with respect to time are said to be at rest. When we are sitting in a moving bus, all are at rest inside the bus with respect to the driver of the bus. But the trees outside are in motion with respect to the same driver inside the bus. Thus rest and motion are relative terms.

2. Vector quantities are important to us because they tell us direction as well as magnitude of a particular quantity. It can give us the exact location of a moving car.

3. Weight: It is the force with which the Earth attracts a body towards it.

The gravitational pull on the moon is about 1/6th of that on the Earth. So, on the moon, a body weighs 1/6th of its weight on the Earth.

4. Yes, an object that moves in a complete circle comes back to its position, then displacement is 0.

5. Refer Fig 2.10 from the textbook.

6. Motion of a screw driver is rectilinear as well as rotatory. A moving cycle, rectilinear as well as rotatory.

1717

D 1. Repetitive motion: Motion that is repeated after a regular interval of time is called repetitive motion. Repetitive motion can be periodic and non-periodic. Periodic motion takes place after regular intervals of time, for

For example, motion of a pendulum.The example of Non periodic is children playing in the park. This motion does not repeat itself after a fi xed interval of time.

2. Scalar quantities: Scalar quantities represent only magnitude. They do not need direction. For example, mass, length, time, speed and temperature.

3. Spring balance: A spring balance measures the weight of an object which is directly suspended from the hook of the spring balance.The principle on which it works is that the extension produced in the spring is directly proportional to the gravitational force acting on it.

4. Curvilinear motion: If an object moves along a curved or circular path, its Motion is called curvilinear motion.For example, a car moving along a curved path.

5. Periodic motion: Periodic motion is a type of repetitive motion that takes place after regular intervals of time. For example, motion of a pendulum, motion of the Earth around the Sun.

6. Acceleration due to gravity: Acceleration due to gravity is the pull of gravity on objects on the surface of the Earth. The gravitational pull on the surface of the moon is one-sixth of that on the Earth.

E. 1. Weight: It is the force with which the Earth attracts a body towards it. The SI unit of weight is Newton. Weight varies from place to place.

Mass: Amount of matter contained in a body. SI unit of mass is kg. Mass is measured using a beam balance.

2. Scalar quantities: Scalar quantities represent only magnitude. They do not need direction. For example, mass, length, time, speed and temperature.

Vector quantities tell us direction as well as magnitude of a particular quantity. For example, it can give us the exact location of a moving car.

3. Uniform motion: When an object moves equal distances in equal intervals of time, the motion is uniform. For example, motion of planets around the Sun.

Non-uniform motion: When an object moves unequal distances in equal intervals of time, the motion is non- uniform. A car moving in crowded market place.

4. Distance: Total length of the actual path covered by a moving object, irrespective of its direction. It is a scalar quantity.

Displacement: Shortest distance travelled by an object from its initial position to its fi nal position in a particular direction. It is a vector quantity.

F 1. Velocity

2. Time

3. Ruler

4. Motion of the Earth

G. 1. Displacement:

AC2 = AB2 + BC2

= 402 m² + 302 m²

= 1600 m² + 900 m² = 2500 m²

AC = 50 m

Distance covered = 70 m

2. Speed = distancetime

= 200 km4 h = 50 km/h

3. Time = distancespeed

= 450 km75 km/h = 6 hours

4. Distance = speed × time

= 12 km/h × 2 h = 24 hours

5. Average speed = Total distance travelled

Total time taken

= (120 + 560) m

(3 + 5) s = 85 m/s

1818

LEARNING ZONE


1. a. Circular motion

b. Zero

c. Uniform speed

d. Distance covered = Circumference of the circle

= 2πr = 2 × 227 × 14 cm = 88 cm

2. a. Rectilinear motion

b. Curvilinear motion

c. Rotatory

d. Translatory and rotatory

e. Vibratory or oscillatory

f. Rotatory

3. Distance covered = Half the circumference

= 12 × 2πr = 227 × 25 m = 78.6 m

Displacement from A to C = 50 m

Think and answer

1. The Earth on which we stand is in motion, as a result everything else is also in motion.

2. Curvilinear and rotatory.

3. The tree is in motion with respect to an observer in space or on the moon


WORKSHEET 1

1. a. motion b. Oscillatory

c. vector d. decreases

2. 1. Random

2. Curvilinear

3. Vibratory

4. Translatory and rotatory

3. a. Distance: Total length of the actual path covered by a moving object, irrespective of its direction. It is a scalar quantity.


b. Vibratory motion is regular to and fro motion of an object. For example, motion of a pendulum, strings of a guitar, etc.

Rotatory motion is circular motion about an axis of rotation. For example,

motion of the blades of a fan, the earth spinning about its axis.

c. Speed = distancespeed

= 5 km40 min = 5 km × 60

40 hr = 7.5 km/h

WORKSHEET 2

1 a. iii b. i

2. a. False b. True

3. 1. ii b. iii 3. iv d. i

4. a. The pull of gravity on objects on the surface of the earth is called acceleration due to gravity. This acceleration decreases as we move upwards from the centre of the Earth. At the equator value of ‘g’ is 9.78 m/s2, and at the poles it is 9.83 m/s2, respectively. For convenience of calculation, acceleration due to gravity is taken as 9.8 m/s2, approximately.

b. Distance = Speed × Time

= 13 × 12 = 6.5 km

1919

Learning Objectives

Students will be able to: learn the concept of energy and mechanical energy such as kinetic and potential

understand the concept of types of energy

understand the concept of law of conservation of energy and energy transformation

3 Energy

Warm-upStudents are made to notice all activities that happen in school, in class and in our immediate surroundings. They are told that each and every activity, natural or man made, requires energy. When we run, or throw a ball, light a fi re, move a vehicle, or when there is rain, thunder and lightning or when an electrical appliance works, energy is used. Energy in one form is converted into another form. For example, when we eat food the chemical energy is converted into muscular energy so that we can do work.

Read the Warm-up section from the book. Use it to explain the types of energy around us.

Concept Explanation

Energy– Read the related sections from the book.

– Light a matchstick and show it to the students. Ask them the type of energy conversion in a matchstick.

– Ask questions to the students such as

Where is the chemical energy present in a matchbox?

How is it converted into heat and light energy?

– Hammer a nail into wood. Ask the students the type of energy present in a raised hammer.

What happens to this energy when the hammer is struck on the nail.

The students are explained about potential energy which is the stored energy and kinetic energy which represents the motion of the hammer, which has the ability to do work, i.e., drive the nail into wood.

Ask the students to answer the related questions from Part II of the Exercises.

Types of Energy– Read the related section from the book.

– Make picture cards, each of which shows a battery, a remote control car, an electric plug, a mixer grinder, a fan, a car battery, a washing machine, a generator, a refrigerator, microwave

– Also make cards of a dam, a turbine, a nuclear reactor, the sun, plants, a solar panel, etc.

2020

– The students are then asked to match the correct picture card to the device that converts one form of energy into another. For For example, The picture of the SUN Solar panel, a green plant etc.

– Picture of electric plug, a fan, a washing machine, a microwave, etc.

Picture of a dam, a turbine, a generator, etc.

Picture of nuclear fusion of uranium nuclear reactor

– Use examples given in the textbook to make the students understand how to understand the different types of energy in an easy way.


Law of Conservation of Energy, Energy Transformation– Read the related sections from the book.

– The students are shown an oscillating pendulum and explained that at the mean position, KE Is maximum and PE is 0, whereas at the extreme position PE is maximum and KE is 0.

Law of conservation of energy can thus be explained.

To reinforce ask the students to do the related Pause and Do section from the book.

Ask the students to answer the related questions from Part II of the Exercises.



2121

Worksheet 1


a. ______________ is the capacity to do work.

b. Natural gas possesses ______________ energy

c. When a ball is thrown up, its _____________ _____________ goes on decreasing.

d. When a substance is heated, the average _____________ _____________ of its molecules increases.

2. Name the following.

a. SI unit of energy. ______________

b. Energy possessed by water stored in a dam. ______________

c. A type of fossil fuel. ______________

d. Vibrations in air. ______________

3. State the energy conversion in the following.

a. Loudspeaker _____________________________________________________

b. Generator _____________________________________________________

c. Photosynthesis _____________________________________________________

d. An electric bulb _____________________________________________________


a. Explain the law of conservation of energy with an example.

_____________________________________________________________________

_____________________________________________________________________

_____________________________________________________________________

b. How is nuclear energy useful to us?

_____________________________________________________________________

_____________________________________________________________________

_____________________________________________________________________

2222

Worksheet 2


a. Falling water has

i. potential energy ii. kinetic energy

iii. chemical energy iv. Heat energy

b. The SI unit of energy is

i. Erg ii. Newton iii. Dyne iv. Joule

2. State True or False:

a. Coal, wood and natural gas possess mechanical energy.

b. Solar energy is utilised by green plants for photosynthesis.

c. When we light a torch, the battery in it converts electrical energy to heat and light energy.

d. Sound is produced by vibrations in air.


a. A compressed spring, Water stored in a dam, moving bullet, a stretched bow, stone placed at a height.

b. Coal, natural gas, water, kerosene, petroleum, wood

c. Calorie, kilocalorie, Newton, Joule

d. Kinetic energy, potential energy, chemical energy, mechanical energy.


a. How is sound produced?

_____________________________________________________________________

_____________________________________________________________________

b. State the energy changes that take place when a pendulum oscillates.

_____________________________________________________________________

_____________________________________________________________________

2323


PART 1

A. 1. (a) 2. (c) 3. (a) 4. (c)

5. (c) 6. (a) 7. (c) 8. (b)

B 1. mechanical energy

2. Energy

3. Sound

4. Heat

5. kinetic energy

6. Coal and charcoal

7. fusion

8. chemical energy

C 1. (e) 2. (a) 3. (d) 4. (c)

5. (b)

D 1. Potential energy to kinetic energy

2. Chemical energy to heat energy

3. Electrical energy to heat energy

4. Electrical energy to mechanical energy

5. Solar energy to heat energy

6. Mechanical energy to electrical energy

PART 2

A. 1. No, work and energy co-exist. Whenever work is done, energy is spent.

2. Energy is the capacity or ability to do work.

3. Kinetic and potential energy

4. SI unit of energy is Joule.

5. Raindrops falling

6. Electric bulb, oil lamp

7. Sound produced by a bell.

8. Muscular energy is used when we use our muscles to do work.

9. Muscular energy is obtained from the chemical energy stored in the food we eat.

B 1. The energy possessed by a body due to its position or state of motion is called

mechanical energy. For example, a rolling ball possess kinetic energy. Water stored in a dam has potential energy.

2. Main source of heat energy is the Sun. Other sources of heat energy are LPG, wood, coal, petrol and kerosene.

3. Electrical energy is used to operate countless electrical appliances at home. It is obtained due to the movement of free electrons in good conductors of electricity such as a copper wire.

4. Magnetic energy is used in electric generators, electronic toys and appliances and to separate magnetic and non-magnetic substances.

5. The hydrogen nuclei around the Sun undergo fusion reaction to form helium

with the release of tremendous amount of energy.

6. Electric fan, mixer grinder and washing machine.

C. 1. Kinetic energy: The energy possessed by an object due to its state of motion.For example, a moving bullet, raindrops falling.

Potential energy: The energy possessed by an object due to its state of rest. For example, a stretched bow, a wound up spring of a watch.

2. The kinetic energy of fl owing water is used to generate electricity in a hydroelectric power plant. The mechanical energy of the turbine is converted into electrical energy.

3. Energy can neither be created nor destroyed. It can only be converted from one form to another, but the sum of all the energy in the universe remains constant.

4. Green plants use solar energy for photosynthesis. They store the food prepared in the form of chemical energy.

5. Electrical energy is used to operate countless appliances at home. It is also

2424

used to light up our homes.

6. Coal, petroleum and natural gas are called fossil fuels. Fossil fuels store energy in the form of chemical energy which is used to move vehicles, used as domestic fuel and provide heat energy.

7. In a pendulum, at each extreme end, potential energy is maximum while at the mean position, i.e., the lowest position kinetic energy is maximum. But the sum of potential and kinetic energy at every instant remains constant.

D 1. Heat energy: It is needed to get warmth, to cook food and to run vehicles. It is obtained from the Sun and by burning fossil fuels.

Light energy: Light helps us to see things around us. Light energy from the Sun is used by green plants to prepare food.

2. Kinetic energy: The energy possessed by an object due to its state of motion.For example, a moving bullet, raindrops falling.

Potential energy: The energy possessed by an object due to its state of rest. For example, a stretched bow, a wound up spring of a watch.

3. Electrical energy is used to operate countless appliances at home. It is also used to light up our homes.

Chemical energy: Plants store food in the form of chemical energy, fossil fuels store chemical energy in the form of heat and light energy.

4. Nuclear energy: Nuclear fi ssion and fusion reactions release nuclear energy. Nuclear fi ssion takes place in the nucleus of radioactive elements. The energy released during fi ssion reaction is used to generate electricity in a nuclear reactor. Nuclear fusion takes place around the Sun.

Heat energy: It is needed to get warmth, to cook food and to run vehicles. It is obtained from the Sun and by burning fossil fuels.

E 1. Generator

2. Windmill

3. Charging of battery

LEARNING ZONE


1. a. chemical energy, electrical energy

b. muscular energy, kinetic energy

c. chemical energy, light energy

d. electrical energy, light and sound energy

Think and answer

1. In a solar thermal power plant, solar energy is converted into electricity using a solar panel or a photo voltaic cell. Thus electricity so obtained is used in homes to run electrical appliances such as television, washing machines, lamps, etc.

2. The electrical energy in the bulb is converted into heat and light energy, Hence, the bulb becomes hot.


WORKSHEET 1

1. a. Energy

b. chemical

c. potential energy

d. kinetic energy

2. a. Joule

b. Potential energy

c. Coal

d. Sound energy

3. a. Electrical energy to sound energy

2525

b. Mechanical to electrical energy

c. Solar energy to chemical energy

d. Electrical energy to light and heat energy

4. a. Law of conservation of energy states that energy can neither be created nor be destroyed, but it can be converted from one form to another. The total energy in the universe remains constant. When raindrops fall to the ground, its potential energy goes on decreasing and kinetic energy goes on increasing, but the total energy at every instant is constant.

b. Nuclear reactions are of two types, nuclear fi ssion and nuclear fusion reactions. The tremendous amount of energy released is controlled in a nuclear reactor where it is used to generate electricity.

WORKSHEET 2

1. a. ii b. iv

2. a. False b. True c. False d. True

3. a. Moving bullet

b. Water

c. Newton

d. Chemical energy

4. a. Sound is produced by vibrations. Sound vibrations can travel through solid, liquid and gas. When the strings of a guitar are struck, vibrations are produced inside the sound box and loud sound is heard. Sound reaches the ear of the listener in the form of energy.

b. In a pendulum, at each extreme end, potential energy is maximum whereas at the lowest position (mean position), kinetic energy is maximum. But the sum of kinetic and potential energy at every instant remains constant.

2626

Learning Objectives

Students will be able to: learn the concept of refl ection at plane mirrors

understand the concept of law of refl ection

understand and defi ne the terms as speed of light and primary colours

Learn the formation of the secondary colours by colour addition

know and understand the appearance of the colour of an object by colour addition

understand the concept of colour subtraction

4 Light Energy

Warm-upStudents are shown a variety of refl ecting materials such as plane mirror, smooth glass table, new steel plate and spoon, and transparent and translucent materials such as a lens, glass slab, a glass of water, butter paper, tinted glass, etc. Ask the students to list the Items as transparent, translucent and opaque. Questions can be asked about the type of image formed in a plane mirror and what happens to light when it is incident on a plane mirror?

Read the Warm-up section from the book.

Use it to explain the properties of light.

Concept Explanation

Refl ection, Important Terms Related to Refl ection, Laws of Refl ection, Refl ection of Light from a Mirror– Read the related sections from the book.

– Explain with diagram that when light rays bounce off the surface of any object, the phenomenon is called refl ection of light.

– Discuss with students the important terms related to refl ection.

– The laws of refl ection are as follows:

• The angle of incidence (i) is equal to the angle of refl ection (r).

• The incident ray, the refl ected ray and the normal at the point of incidence all lie in the same plane.

– To reinforce, demonstrate the related experiment given in this section.

– To reinforce ask the students to do the related Pause and Do section from the book.


Plane Mirror, Formation of Images Through a Plane Mirror, Characteristics of the Image Formed by a Plane Mirror– A plane mirror is shown to the class.

– The students are shown various images of different objects kept in class including their own image. Cards of a few letters

2727

of English alphabet such as P, Q, R ,M, Z, etc are fi rst shown to the students and then their image in the mirror is shown.

– They are asked questions on the characteristics of the image formed in a plane mirror and how far is the image from the mirror compared to the object.

– Read the related sections from the book.

– Demonstrate how to form the image of a point object and a large object.

– Discuss the characteristics of the image formed by a plane mirror.



Speed of Light, Primary Colours, Formation of Secondary colours, Complementary Colours, Appearance of the Colour of an Object, Colour Subtraction– Students are shown a red rose, a green

leaf, the blackboard and the white wall of the classroom. They can be asked of why do these objects appear of that particular colour to them? Which property of light gives them that particular colour? Responses of the students are listed.

– They are told that Sir Isaac Newton was the fi rst scientist who discovered through experiments that white light is composed of seven colours. He used a prism to split white light into seven colours in the order of VIBGYOR, which stands for violet, indigo, blue, green, yellow, orange and red. It is one or a combination of these

colours which gives an object its specifi c colour.

– Show a glass prism to the students and hold it at a certain angle to obtain a spectrum.

– The concept of primary and secondary colours is explained to the students by making a colour disc.

– In this activity the students are separated into groups and asked to cut out a circle of cardboard or thermocole, divide it into seven sections and paint each section with the seven colours of the rainbow. A hole is pierced in the centre of the colour discs and they are made to rotate with great speed. What the students will observe is a white circle instead of the seven colours they had painted. This proves that white light is composed of seven colours.

– The three blades of the fan can be painted red, blue and green which on rotation would give white colour. Thus red, blue and green are called primary colours.





2828

Worksheet 1


a. The bouncing back of incident light from a smooth polished surface is called ______________.

b. Angle of incidence is ______________ to the angle of refl ection.

c. A ______________ image is always inverted.

d. A green leaf refl ects only ______________ colour.


a. A line drawn perpendicular to the refl ecting surface. ______________

b. The right hand side of the object appears as the left hand ______________side of the image.

c. Image that cannot be obtained on a screen ______________

d. Colour of an object in different light can be determined ______________by this method


a. Refl ected ray, incident ray, refracted ray, normal, point of incidence

b. Real, erect, virtual, laterally inverted


a. What are pigments?

_____________________________________________________________________

_____________________________________________________________________

_____________________________________________________________________

b. Draw a ray diagram to prove the laws of refl ection. Label the rays correctly.

_____________________________________________________________________

_____________________________________________________________________

_____________________________________________________________________

2929

Worksheet 2


a. If the incident ray on a refl ecting surface is along the normal, the angle of incidence will be

i. 300 ii. 450 iii. 00 iv. 900

b. The distance of the image in front of the plane mirror is

i. same distance as the object ii. greater distance as the object

iii. less distance than the object iv. None of these

c. In blue light the sunfl ower will appear

i. blue ii. yellow iii. cyan iv. black


a. Red, blue and green i. White light

b. Magenta, cyan and yellow ii. Complementary colours

c. Blue and yellow iii. Primary colours

d. Spectrum iv. Secondary colours


a. State the laws of refl ection.

_____________________________________________________________________

_____________________________________________________________________

_____________________________________________________________________

_____________________________________________________________________

b. What is lateral inversion? How would the image of letter ‘R’ appear in a plane mirror?

_____________________________________________________________________

_____________________________________________________________________

_____________________________________________________________________

_____________________________________________________________________

3030


PART 1

A 1. (b) 2. (b) 3. (a) 4. (c)

6. (a) 7. (d) 8. (d)

B. 1. refl ection 2. completely

3. refl ection 4. mirror

5. of the same size 6. laterally

7. seven 8. black

C. 1. T 2. T 3. F 4. T 5. F

6. T 7. T 8. F 9. T

D 1. Red, blue and green 2. Magenta

3. Angle of incidence 4. Normal

5. Refl ection 6. Incident ray

7. Refl ected ray 8. Angle of refl ection

PART 2

A. 1. Angle of refl ection will also be 450

2. Virtual and erect

3. The alphabets of the word AMBULANCE are laterally inverted.

4. Red, blue and green

5. Magenta, cyan and yellow.

6. Coal absorbs all the colours of incident white light and refl ects none.

B. 1. The phenomenon of change in the direction of a ray of light after striking a surface, through which it cannot pass.

2. A plane mirror is a completely smooth refl ecting surface, through which light cannot pass.

3. a. The angle of incidence is equal to the angle of refl ection.

b. The incident ray, the refl ected ray and the normal at the point of incidence all lie in the same plane.

4. Any smooth, polished surface which can refl ect back the rays of light incident on it is a refl ecting surface.

5. When the right side of the image in a plane mirror appears to be the left side, it is called lateral inversion.

6. Real image: Inverted and can be formed on a screen.

Virtual image: Erect and cannot be formed on a screen.

7. A pigment is an optically active substance which absorbs most of the colours of white light and selectively refl ects one or more colours.

C. 1. Terms related to refl ection of light,

a. Incident ray: A light ray falling on a refl ecting surface is called an incident ray.

b. Normal: A line drawn perpendicular to the refl ecting surface at the point of incidence.

c. Refl ected ray: A ray of light which returns back to the same medium after striking the refl ecting surface.

d. Angle of incidence: The angle between the incident ray and the normal.

e. Angle of refl ection: The angle between the refl ected ray and the normal.

2. The colour of an object in different light can be determined by the method of colour subtraction. For example,a ball that is made of a material which absorbs red colour will appear cyan to the players. When we subtract red colour from white light, we get cyan according to the equation,

White light – Red

(Red + blue + green) – Red

Red gets cancelled. What remains is (blue + green)

Blue + green = Cyan.

So the ball appears cyan colour. Another name for cyan is peacock blue.

3131

3. On a sheet of white paper draw a line MM’ representing the mirror surface. Mark a point O at a distance of 3 cm in front of the line MM’.

Draw two incident rays on the mirror surface. At the point of incidence draw two perpendiculars as shown in the diagram. Draw the refl ected rays and produce them backwards till they meet at point I. I is the image of the point object O. Measure distance OM and IM. OM = IM. (Refer Fig. 4.7 from the textbook)

4. The three colours red, blue and green which combine to produce white light are called primary colours.Yes, secondary colours can be formed by mixing any two primary colours. For example,

Red + Blue = Magenta 5. a. In green light the rose will appear

black. The red rose will absorb the green colour and refl ect none. Hence, the rose will appear black.

b. In red light it will appear red. The red light which falls on the red rose will be refl ected back and the rose will appear red only.

6. Characteristics of image formed by a plane mirror,

a. The image is erect and laterally inverted.

b. It is the same size as the object. c. The image is as far behind the mirror as

the object is in front of it. d. The image formed is virtual. 7. A piece of paper appears white in Sunlight

because it refl ects back all the colours of incident white light. It will appear red in red light.

8. It will appear black in red light, because the paper will absorb the red light.

D 1. Point of incidence: It is a point on the refl ecting surface where the incident ray strikes.

2. Normal: It is the perpendicular drawn on the refl ecting surface at the point of incidence.

3. Refl ecting surface: Any smooth polished surface which can refl ect back the rays

of light incident on it.

4. Complementary colours: A pair of colours, one primary and the other secondary, which on mixing form white light are called complementary colours.

5. A pigment is an optically active substance which absorbs most of the colours of white light and selectively refl ects one or more colours.

E. 1. Incident ray: A light ray falling on a refl ecting surface is called an incident ray.

Refl ected ray: A ray of light which returns back to the same medium after striking the refl ecting surface.

2. Angle of incidence: The angle between the incident ray and the normal.

Angle of refl ection: The angle between the refl ected ray and the normal.

3. Real image: Inverted and can be formed on a screen.


4. The three colours red, blue and green which combine to produce white light are called primary colours.

Secondary colours can be formed by mixing any two primary colours. For example, Red + Blue = Magenta.

LEARNING ZONE


1. a. Fig (a)

b. Incident ray: AO,

Angle of refl ection: BON

Refl ected ray: OB

c. ON : Normal

d. Angle of incidence = angle of refl ection

2. a. The refl ected ray is along the normal.

b. Refl ected ray is OB.

c. Refl ected ray is OA.

3232

3. a. Angle of incidence = 0°

b. Angle of incidence = 30°

c. Angle of incidence = 45°

Think and answer

1. The shiny metal utensil is not as smooth as a

mirror hence the image is not very clear.

2. The image is formed exactly behind the joint of the two mirrors.

3. The new refl ected ray would be where the incident ray was in the opposite direction.

Answers to Assessment 1A 1. (c) 2. (c) 3. (c) 4. (c) 5. (d)

B 1. Periodic motion: If an object repeats its motion after a certain interval of time, then the object is said to have periodic motion.

2. Average speed: It is the ratio of the total distance travelled to the total time taken for the journey.

3. Scalar quantity: quantity that have only magnitude and no direction are called Scalar quantities. For Eg. Volume, area, speed etc.

4. Potential energy: It is the energy possessed by a body due to its state of rest. Eg. A stone placed at a height, a stretched bow etc.

5. Lateral inversion: When the sides of the image in a plane mirror are interchanged, It is called lateral inversion.

C 1. (d) 2. (c) 3. (b) 4. (e)

5. (a)

D 1. Volume 2. Vector

3. Energy 4. Kinetic energy

5. Angle of refl ection

E. 1. Real image: Inverted and can be formed on a screen.


2. The three colours red, blue and green which combine to produce white light are called primary colours. Secondary colours can be formed by mixing any two primary colours. For eg. Red + Blue = Magenta

3. Kinetic energy: The energy possessed by an object due to its state of motion.

Eg. A moving bullet, raindrops falling.

Potential energy: The energy possessed by an object due to its state of rest.

Eg. A stretched bow, a wound up spring of a watch.

4. Distance: Total length of the actual path covered by a moving object, irrespective of its direction. It is a scalar quantity.


5. Scalar quantities: Scalar quantities represent only magnitude. They do not need direction. Eg. Mass, length, time, speed and temperature.

Vector quantities tell us direction as well as magnitude of a particular quantity. For eg. It can give us the exact location of a moving car.

F 1. T 2. T 3. T 4. F 5. T

G 1. A plane mirror is a completely smooth refl ecting surface, through which light cannot pass.

2. a. The angle of incidence is equal to the angle of refl ection.

b. The incident ray, the refl ected ray and the normal at the point of incidence all Lie in the same plane.

3. Distance covered in unit time is called speed.

4. Density is mass per unit volume. Unit: kg/m3

5. Spring balance.

3333

6. Vector quantity measures both magnitude and direction.

7. Rectilinear motion and periodic motion.H 1. Terms related to refl ection of light, i. Incident ray: A light ray falling on a

refl ecting surface is called an incident ray.

ii. Normal: A line drawn perpendicular to the refl ecting surface at the point of incidence.

iii. Refl ected ray: A ray of light which returns back to the same medium after striking the refl ecting surface.

iv. Angle of incidence: The angle between the incident ray and the normal.

v. Angle of refl ection: The angle between the refl ected ray and the normal.

2. Conversion of one form of energy into another is called energy transformation.

For Eg. Green plants use solar energy for photosynthesis. They store the food prepared in the form of chemical energy.

Electrical energy is used to operate countless appliances at home. It is also used to light up our homes. Coal, petroleum and natural gas are called fossil fuels. Fossil fuels store energy in the form of chemical energy which is used to move vehicles, used as domestic fuel and provide heat energy.

3. A spring balance measures the weight of an object which is directly suspended from the hook of the spring balance. The pointer shows the weight of the object directly. The principle on which it works is that the extension produced in the spring is directly proportional to the gravitational force acting on it.

4. On a sheet of white paper draw a line MM’ representing the mirror surface. Mark a point O at a distance of 3cm in front of the line MM’.

Draw two incident rays on the mirror surface. At the point of incidence draw two perpendiculars as shown in the diagram. Draw the refl ected rays and produce them backwards till they meet at point I. I is the image of the point object O. Measure distance OM and IM. OM = IM. (Diagram)

5. The colour of an object in different light can be determined by the method of colour subtraction. For eg. A ball that is made of a material which absorbs red colour will appear cyan to the players. When we subtract red colour from white light, we get cyan according to the equation, White light – Red

(Red + blue + green) – Red

Red gets cancelled. What remains is (blue + green)

Blue + green = Cyan.

So the ball appears cyan colour. Another name for cyan is peacock blue.

I. 1. The characteristics of the image formed by a plane mirror is virtual, erect, laterally inverted and as far behind the mirror as the object is in front of it.

2. The object and the image are at equal distance from the mirror.

3. A virtual image cannot be obtained on the screen.

4. The rays of light are refl ected back. They are produced back to meet at a point to form the image behind the mirror.

Answers to WorksheetsWORKSHEET 1

1. a. refl ection b. equal

c. real d. green

2 a. Normal b. Lateral inversion

c. Virtual d. Colour subtraction

3. a. Refracted ray b. Real

3434

4 b. A pigment is an optically active substance which absorbs most of the colours of white light and selectively refl ects one or more colours. By themselves pigments have no colour. The colour gets activated only when the pigments are exposed to white light.

b. AN

normal

angle of refl ecti on

refl ected ray

angle of incidence

incident ray

B

M M’O

i ri = r

WORKSHEET 2

1. a. iii b. i c. iv

2. a. iii b. iv c. ii d. i

3. a. i. The angle of incidence is equal to the angle of refl ection.

ii. The incident ray, the refl ected ray and the normal at the point of incidence all lie in the same plane.

b. When the right side of the image in a plane mirror appears to be the left side, it is called lateral inversion. Image of ‘R’ will appear laterally inverted.

3535

Total marks: 50Time: 3 hours

Model Test Paper 1

Section AA. Fill in the blanks. [5]

1. ________________ forms a convex meniscus.

2. The ________________ of a substance is mass per unit volume.

3. Falling water has ________________ energy.

4. The speed of a car covering a distance of 215 km in 5 hours is ________________.

5. ________________ is a line drawn perpendicular to the refl ecting surface.

B. Multiple choice questions. [5]

1. If a body covers equal distances in equal intervals of time, then the motion is said to be

a. Non-uniform b. Rotatory c. Uniform d. Random

2. When coal burns

a. Chemical energy changes into heat energy

b. Photochemical energy changes into heat energy

c. Chemical energy changes into kinetic energy

d. None of these

3. The angle of incidence at the point of incidence is

a. Greater than angle of refl ection b. Less than angle of refl ection

c. Equal to angle of refl ection d. Can be greater or less than angle of refl ection

4. A black surface is a

a. a good refl ector b. A good absorber c. A good radiator d. None of these

5. One litre is

a. 1 cm3 b. 1 m3 c. 10–3 m3 d. 10–3 cm3

C. State True or False. [5]

1. Nuclear energy is used to generate electricity in a nuclear power plant.

2. Petrol and diesel possess fuel energy.

3. A virtual image is always erect.

4. Two primary colours combine to form a complementary colour.

5. A tumbler measure is used by a chemist in a dispensary.

D. Circle the odd one out. [4]

1. Volume, area, mass, length, thickness

2. Oscillatory motion, translatory motion, curvilinear motion, random motion, rotatory motion

3636

3. Chemical energy, muscular energy, kinetic energy, mechanical energy, solar energy

4. Incident ray, refl ected ray, virtual image, normal, point of incidence.

Section BA. Defi ne the following. [3]

1. Kinetic energy

2. Acceleration due to gravity

3. Complementary colours

B. Short answer questions. [12]

1. Name three electrical appliances that convert electrical energy into mechanical energy.

2. Give the difference between real image and virtual image.

3. A fl ower vase appears blue in white light. What colour will it appear in

a. green light b. blue light?

Give your reason in each case.

C. Long answer questions. [16]

1. What are fossil fuels? How are they useful.

2. With the help of a neat ray diagram explain how you will draw the image of a point object placed in front of a plane mirror.

3. With the help of any two examples , explain that a body can have two or more types of motion simultaneously.

4. The mass of an iron plate of density 4.5 g/cm3 is 45 g. Calculate its volume.

3737

Learning Objectives

Students will be able to: learn the concept of heat and different units of temperature

understand the effects of heat in our daily life

understand the concept of temperature scales and change in state

learn the application of expansion and contraction

understand the concept of transfer of heat

learn the concept of conduction, convection, and radiation

understand the concept of thermos fl ask

5 Heat

Warm-upThe students are asked questions like,(i) Why are cooking utensils made of metal like copper and aluminium? (ii) Why do we feel hot under the sun? (iii) Why are rooms that have no ventilators are exceptionally warm?(iv) or Why are telephone wires kept loose between the two poles? Answers to these and many more questions are taken from the students at random. The teacher then arrives at the conclusion that heat is conducted in different ways, namely, conduction, convection and radiation. The teacher can explain many more applications of heat.

Picture cards of the various modes of heat transfer are shown, and the students are asked to classify them under three different headings.


Use it to explain the concept of heat transfer.

Concept Explanation

Heat, Different Units of Temperature, Effects of Heat in our Daily Life, Temperature Scales, Change in State, Applications of Expansion and Contraction– Read the related sections from the

textbook.

– Cold water, normal tap water and hot water are taken in three different glasses.

– Students are shown a laboratory thermometer. One by one they are asked to record the temperature of water in the glasses. The temperatures are noted. The water of the two glasses containing hot and cold water is mixed.

– The temperature of the mixture is noted again.

– Thus the concept of thermal equilibrium is explained to the students.

– The teacher takes a clinical thermometer and a laboratory thermometer and

3838

asks the students to record their body temperature and temperature of normal readings in both Celsius and Fahrenheit scales. The relationship between the two scales is then derived and comparison between the two scales is shown on the board.

– To reinforce, demonstrate the related experiments given in these sections.



Transfer of Heat, Conduction of Heat, Uses of Good and Bad Conductors of Heat – Read the related sections from the

textbook.

– Explain that due to the difference in the temperatures between the two bodies in contact, heat fl ows from a hot body to a cold body, that is, from a higher temperature to a lower temperature.

– Explain the concept of conduction of heat.

– Discuss with students the uses of good and bad conductors of heat.

- To reinforce, demonstrate the related experiments given in these sections.

– To reinforce, ask the students to do the related Pause and Do section from the book.

– Ask the students to answer the related

questions from the Part II of the Exercises.

Convection, Radiation, Thermos Flask – Read the related sections from the

textbook.

– Explain that convection is a mode of heat transfer in which heat energy is transferred from one part to another by the actual movement of the molecules of the medium.

– Discuss the practical applications of convection currents.

– Explain that the mode of transmitting heat that does not require a medium is known as radiation.

– Demonstrate the concept of thermos fl ask to the students.






3939

Worksheet 1


a. The degree of hotness or coldness of a body is called its ______________.

b. ______________ is a rapid chemical change in which heat and light are produced.

c. Dew drops formed on the grass early in the morning is an example of ______________.

d. Steam pipes fi tted with loops are called ______________ joints.

2. State True or False.

a. On the Celsius scale, the freezing point of water is 32°F.

b. In conduction, heat is transferred by the actual movement of the molecules of a medium.

c. Land breeze and sea breeze are formed due to convection currents in air.

d. Solids expand the least and gases expand the most on heating.


a. SI unit of heat. _________________

b. SI unit of temperature. _________________

c. An infl ammable material. _________________

d. A good conductor of heat. _________________


a. What is sublimation? Give two examples of sublimation.

_____________________________________________________________________

_____________________________________________________________________

_____________________________________________________________________

b. Give the different uses of a bimetallic strip.

_____________________________________________________________________

_____________________________________________________________________

_____________________________________________________________________

4040

Worksheet 2


a. It is an infl ammable substance:

i. Ceramic ii. Petrol iii. Rubber iv. Brick

b. In convection, heat travels

i. upwards ii. sideways iii. downwards iv. in all directions

c. Water boils at

i. 100 °F ii. 212 °F iii. 212 °C iv. none of these

d. In sublimation, there is a change of state from

i. solid to liquid ii. gas to solid iii. solid to gas iv. none of these


a. Radiation i. Land and sea breeze

b. Boiling ii. Thermostat switch

c. Conduction iii. No medium is required

d. Convection iv. Takes place at a fi xed temperature

e. Bimetallic strip v. Transfer of heat energy only


a. What is thermal equilibrium?

_____________________________________________________________________

_____________________________________________________________________

b. Compare the Celsius and Fahrenheit scales of temperature with the help of diagrams of the two thermometers.

_____________________________________________________________________

_____________________________________________________________________

c. A hot iron ball is hung from the roof of a room. State the different ways in which it will lose heat.

_____________________________________________________________________

_____________________________________________________________________

4141


PART 1

A 1. (b) 2. (b) 3. (a) 4. (c)

6. (a) 7. (d) 8. (d)

A 1. (b) 2. (c) 3. (d) 4. (b)

5. (a) 6. (a) 7. (d)

B 1. more 2. less

3. temperature 4. 180 divisions

5. infl ammable 6. infl ammable

7. thermometer 8. absorbs

9. maximum

C. 1. T 2. T 3. F 4. T

5. T 6. T 7. T 8. F

D. 1. Celsius

2. Convection

3. Thermometer

4. Conduction

5. Radiation

PART 2

A 1. The degree of hotness or coldness of a body is called its temperature.

2. A Scottish engineer, mathematician and physicist, Lord Kelvin invented the Kelvin Scale.

3. Mercury

4. The molecular arrangement is different in solids, liquids and gases, hence expansion

is different.

5. Conduction occurs in metals. For example, metals and their alloys are used in making utensils.

6. We feel hot near a fi re.

7. Land and sea breeze. Water is always heated from below.

8. Plastic, wood

9. Copper and silver.

B 1. The warm air from the heater rises up, and the cool air of the room descends down to

take its place. Thus convection currents are set up and the whole room gradually gets heated.

2. Dark coloured clothes are worn in winter because they absorb heat and keep us warm.

3. Solar energy is easily available and cheap source of energy. Solar cells, solar cookers

and water heaters are specially designed to absorb maximum solar radiation without polluting the atmosphere.

4. The particles of a solid gain kinetic energy and the space between the particles increases slightly, hence solids expand on heating but to a very small extent. In other words expansion is negligible in solids.

5. This is because of unequal expansion of the inner and outer surface of the bottle. The outer surface contracts more than the inner surface on coming in contact with cold water.

6. Bimetallic strip is used to turn a pointer or close a switch. The thermostat switch is used in refrigerators, ovens and toasters to control the heat.

7. A glass fl ask fi tted with a capillary tube is initially fi lled with water. The level of water is noted and then the fl ask is heated over a burner. Water level gradually rises in the capillary tube showing liquids expand on heating.

C 1. In good conductors such as copper, silver and aluminium molecules are closely packed, vibrating about their mean position.When one end of the metal rod is heated the vibrating molecules collide with the neighbouring molecules and transfer a part of heat energy to them. In this way the neighbouring molecules start vibrating and heat is transferred from the

4242

hot end of the metal rod to cold end. This happens without the transfer of molecules. Only energy is transferred. In insulators or bad conductors such as wood, paper, glass, etc., particles are farther apart. There is less chance of particles colliding and passing on the heat energy.

2. Conduction: A medium is required for transfer of heat by conduction. The process is slow.

Convection: A medium is needed for transfer of heat. The process is faster than conduction.

Radiation: Radiation occurs in vacuum.

It is the fastest process. Speed equal to the speed of light.

3. Metals and their alloys are used in making utensils. Copper wire is used to make electrical cables.

4. Refer Fig. 5.5 from the textbook.

5. Refer Fig. 5.9 from the textbook.

The cork stopper prevents heat loss by conduction. Silver coating reduces heat loss by radiation. Glass walls reduce heat loss by conduction. Vacuum reduces heat loss by conduction and convection.

6. Heat fl ows from a body at a higher temperature to a lower temperature till both bodies attain equal temperature. This is a state of thermal equilibrium.

7. Two effects of heat:

Fire: It is a rapid chemical change in which heat and light are produced. Certain infl ammable substances have low ignition temperature. Wood, coal, kerosene, Petrol, etc., burn easily and are called infl ammable substances.

Change in temperature: When a body is heated its temperature rises and when it is cooled its temperature decreases. The change in temperature depends on, (a) quantity of heat supplied, and (b) material of the body.

8. The Celsius scale has 100 equal divisions with 0°C being the freezing point of ice

and 100°C, the boiling point of water. The Fahrenheit scale has 180 equal divisions with 32°F as the lowest temperature corresponding to 0 °C on the Celsius scale and 212 °F as the highest temperature corresponding to 100 °C. The Fahrenheit scale is more accurate than the Celsius scale.

9. The Celsius and the Kelvin scale both have 100 equal divisions.

10. Infl ammable substances have low ignition temperature. Wood, coal, kerosene, Petrol, etc, burn easily and are called infl ammable substances.

11. Evaporation: It is a slow process. It takes place at all temperatures. Evaporation causes cooling.

Boiling: It is a quick process. It takes place at a fi xed temperature. It does not cause cooling.

D 1. Temperature: It is the degree of hotness or coldness of a body.

2. Conduction: Transfer of heat from one end of a metal rod such as copper or silver to the other end by the vibration of molecules of the medium which only transfer the heat energy but do not move themselves.

3. Insulators: Insulators such as wood, rubber, plastic, etc., are poor conductors. The particles do not gain enough kinetic energy to transfer the heat from one end to the farthest end.

4. Radiation: Transfer of heat energy that takes place without the movement of the medium particles, such as that in vacuum is called radiation. It is transmitted in the form of electromagnetic waves. For example, we feel hot under the Sun.

5. Heat energy: Heat is a form of energy that fl ows from one body to another due to the temperature difference between them. Heat energy is the sum total of the kinetic energy of all the molecules moving inside a body.

6. Conductors: Materials that allow heat to pass through them easily are known as

4343

good conductors of heat. For example, iron, copper and silver are good conductors because the particles in them are close together.

7. Convection: In convection, heat is transferred by the actual movement of the particles of the medium. Convection occurs in liquids and gases only where the molecules are loosely packed and are free to move. Convection currents occur from bottom upwards.

E. 1. Black is a good absorber of heat, hence cooking utensils are blackened at the bottom.

2. The molecules in solids are tightly packed with hardly any intermolecular space between them. For convection to occur there should be large space between molecules.

3. Steam pipes are fi tted with loops called expansion joints. When steam or hot water is passed through these pipes, the loops allow the pipes to expand easily.

4. Oil tankers carry infl ammable substances such as petrol and diesel, during summer.The non-conducting material of the tanker minimises the loss of heat due to evaporation and prevents a fi re due to excessive heating of substances.

5. Woolen clothes do not allow our body heat to escape to the surroundings during winter due to trapped air between their pores. Air is a poor conductor of heat, hence it does not allow the body heat to escape.

F. 1. K = 100 + 273, = 373 K

2. K = 45 + 273, = 318 K

3. °F = (°C × 9/5) + 32

= (100 × 9/5) + 32

= 180 + 32 = 212 °F

4. °C = (°F – 32) × 5/9 = (65 – 32) × 5/9

= 33 × 5/9 = 18.3 °C

5. °F = (°C × 9/5) + 32

= (–40°C × 9/5) + 32= –40°F

6. K = 37 + 273 = 310 K

LEARNING ZONE


1. After 1 hour,

(a) All the ice will be melted

(b) Water

(c) Ice absorbed heat

(d) Melting

(e) 0 °C

After 1 week,

(a) The water seems to be evaporated

(b) Water has changed into vapour

(c) Vaporization

(d) 100 °C

2.

Radiati on

Convecti on

Conducti on

The process of heat transfer are convection, conduction and radiation.

3. (a)

(b) These phenomenon occur because of convection currents which are caused because of unequal heating of land and sea during the day and night.

4444

(c) During the day there is sea breeze.

During the night there is land breeze.

4. (a) Silver coating reduces heat loss due to radiation.

(b) Vacuum reduces heat loss due to conduction and convection.

(c) Plastic being an insulator is a bad conductor of heat.

Think and answer

1. (a) Heat energy reaches us only by radiation because for convection and conduction to take place we need a medium to transmit heat. Radiation can occur even in vacuum.

(b) We feel hot in the Sun.

A lighted bulb radiates heat.

2. The ice will melt quickly.

The second ice cube will also melt but much slower than the fi rst one.

3. White colour is a good refl ector of heat and keeps the house cool.

4. Cloudy nights trap the heat within the earth’s atmosphere.

5. The glass of milk with the steel spoon will cool faster. This happens because steel is a good conductor and transmits the heat quickly away.


WORKSHEET 1

1. a. temperature

b. Fire

c. condensation

d. expansion

2. a. False b. False

c. True d. True

3. a. Joule

b. Kelvin

c. Petrol

d. Copper

4. a. Sublimation: The change of state from a solid to a gas directly without passing through the liquid state is called sublimation. Heat energy is absorbed.

For example, moth balls, camphor and dry ice.

b. Bimetallic strip may be used to turn a pointer or close a switch. It is used in a thermostat. Refrigerators, ovens and toasters use thermostat switches to control The heat.

WORKSHEET 2

1. a. ii b. i c. ii d. iii

2. a. iii b. iv c. v d. i

e. ii

3. a. Heat fl ows from a body at a higher temperature to a lower temperature till both bodies attain equal temperature. This is a state of thermal equilibrium.

b. The Celsius scale has 100 equal divisions with 00C being the freezing point of ice and 100 °C, the boiling point of water.

The Fahrenheit scale has 180 equal divisions with 32 °F as the lowest temperature corresponding to 0 °C on the Celsius scale and 212 °F as the highest temperature corresponding to 100 °C. The Fahrenheit scale is more accurate than the Celsius scale.

c. The iron ball hanging by a thin wire, loses heat by conduction through the thin metal wire, loses heat by radiation so the room gets heated up and warm air rises up, hence convection currents are set up.

4545

Learning Objectives

Students will be able to: learn the concept of source of a sound

understand the sound as a longitudinal wave

understand why sound requires a medium to propagate

understand the characteristics of a sound wave

learn the concept of refl ection and absorption of sound

know and learn the concept of relative speed of sound in different medium

6 Sound

Warm-upStudents are asked not to make noise because it is causing the teacher a headache. Too much sound can make one sick causing physical and mental disturbance. The soft music of a harmonium coming from the concert hall, is soothing and pleasant. Thus the difference between music and noise is explained. The teacher then stretches a rubber band between the two fi ngers and asks a student to give it a slight tug. Everyone notices that the rubber band begins to vibrate. The vibrations are so quick that it is impossible to perceive them as separate vibrations or even count them.

Students are told they are going to study ‘Sound’. They will understand the difference between music and noise.

Read the Warm-up section from the book. Use it to explain the concept of music and noise.

Concept Explanation

Sources of Sound, How Sound is Produced– A tuning fork struck against a rubber pad

is brought near the ear of some students. They can perceive the vibrations and hear a buzzing sound.

– Picture cards of water waves, traffi c sounds, children playing the guitar and a drum, playing the fl ute, etc. are shown to the class and the students are asked, what is one thing that is common to all the pictures shown.

– They arrive at the conclusion that it is ‘Vibrations’ that are responsible for all the sounds shown in the pictures.


– To reinforce, demonstrate the related activity given in these sections.


4646

Sound as a Longitudinal Wave, Sound Needs a Medium to Propagate, Characteristics of a Sound Wave– One student is asked to bring a slinky,

which is a long coil of very thin metal just like a spring.

– The slinky is pulled apart and pushed together like you would do to a spring. The teacher can explain longitudinal waves using the slinky. Where the air particles are close together it is compression and where they are far apart it is rarefaction. Such longitudinal waves occur in air.


– Discuss with students the characteristics of a sound wave.

– To reinforce, demonstrate the related activities given in these sections.



Echoes, Sonar, Relative Speed of Sound in Different Mediums – The concept of echo can be explained

by taking the students to the school auditorium and to an open space where there is a large building in the background. They are asked to scream loudly and then silently asked to hear if there is any refl ected sound. In the auditorium there is no echo, because of sound absorbing material like, carpets, curtains and soft boards.

But out in the open they can clearly hear an echo. Conditions for an echo is then explained.

– To reinforce, demonstrate the related activity given in these sections.





4747

Worksheet 1


a. ______________ is produced when a body vibrates.

b. Sound waves in air are called ______________ waves.

c. A fl y can fl ap its wings back and forth ______________ times in one second.

d. The refl ection of sound causes ______________.


a. The speed of sound increases with decrease in temperature.

b. Frequency of a wave is inversely proportional to its time period.

c. The intensity of sound is measured in Hz.

d. A wave is a disturbance that carries only energy and not particles of the medium.


a. Number of vibrations passing through a point in one second. ________________

b. Good refl ector of sound. _________________

c. Speed of sound in water. _________________

d. A device used to fi nd the depth of the sea. _________________


a. State the factors on which the speed of sound in different medium depends.

_____________________________________________________________________

_____________________________________________________________________

_____________________________________________________________________

b. How do bats avoid obstacles in their path?

_____________________________________________________________________

_____________________________________________________________________

_____________________________________________________________________

4848

Worksheet 2


a. The unit of frequency is

i. Meter ii. Second iii. Hertz iv. per meter

b. Loudness of a sound wave is measured by its

i. amplitude ii. wavelength iii. time period iv. frequency

c. Crests and troughs are found in

i. longitudinal waves ii. transverse waves

iii. electromagnetic waves iv. None of these

d. The minimum distance for an echo to be heard is

i. 165 m ii. 19.5 m iii. 320 m iv. 16.5 m


a. 340 m/s, 1480 m/s, 5120 m/s, 100 m/s

b. Frequency, Compression, Time period, Amplitude, Wavelength

c. Pitch, Compression, Rarefaction, Crest, Trough

d. Quality, Timbre, Pitch, Loudness, Refl ection


a. What are the conditions for an echo to be heard?

_____________________________________________________________________

_____________________________________________________________________

b. How is SONAR used to locate shoals of fi sh or measure the depth of the ocean?

_____________________________________________________________________

_____________________________________________________________________

c. A pendulum makes 120 oscillations in 24 seconds. Calculate its frequency and the time period.

_____________________________________________________________________

_____________________________________________________________________

4949


PART 1

A 1. (a) 2. (a) 3. (d) 4. (a)

5. (c) 6. (c) 7. (a) 8. (a)

B 1. oscillatory 2. waves

3. air 4. radio waves

5. 256 6. decreases

7. high 8. More

9. refl ectors

C 1. F 2. F 3. T 4. F

5. T 6. T 7. F 8. T

D 1. (c) 2. (d) 3. (b) 4. (a)

5. (f) 6. (e)

PART 2

A 1. Sound is produced by vibrations in a medium.

2. Sound is a form of energy which is produced when a body vibrates. This energy is transmitted in a medium in the form of waves.

3. Musical instruments, humans and animals produce sound.

4. Sound is produced when an object vibrates. Humans produce sound due to the vibrations of air produced in the sound box. Musical instruments like the guitar produce sound because of vibrations of its strings.

5. To and fro motion of an object during which the vibrating body assumes a new

shape is called vibratory motion. Vibratory motion is repetitive.

6. Hertz

7. Meter

8. Walls and rocks are good refl ectors of sound.

9. Curtains and wood are good absorbers of sound.

B 1. In a longitudinal wave the area where the air particles lie away from each other creating region of low pressure, is called rarefaction.

2. Frequency of a wave is inversely proportional to time period.

3. Number of waves passing through a point in one second is called frequency.

4. An echo is the sound heard after its refl ection from a rigid surface, such as a cliff or hillside, a wall or any obstructing surface. The minimum distance of the refl ecting surface from the source of sound should be 16.5 m for an echo to be heard.

5. SONAR stands for, Sound, Navigation and Ranging.

6. Sound cannot travel through vacuum.

Take some water in a bottle. Boil the water to drive out the air in the bottle. Through a one holed cork hang a bell inside the bottle. There is vacuum inside the bottle.pull the thread hanging outside the bottle. You can see the bell shaking but cannot hear its ring. This proves that sound does not travel through vacuum.

7. People cannot hear each other on the moon. The reason is that there is no atmosphere on the moon, and hence no medium to propagate sound waves. Astronauts use radio-waves to communicate with each other.

C 1. Sound is a form of energy which is produced when a body vibrates. This energy is transmitted in a medium in the form of waves. Musical instruments, humans and animals produce sound.

Sound is produced when an object vibrates. Humans produce sound due to the vibrations of air produced in the sound box. Musical instruments like the guitar produce sound because of vibrations of its strings.

5050

2. Sound waves in air that produce alternate areas of compression and rarefaction are called longitudinal waves. Longitudinal waves travel along the direction of propagation of the wave particles.

3. Compression is an area of high pressure where the air particles are close to each other whereas rarefaction is an area of low pressure where the air particles are far apart.

4. The pitch and hence frequency of a piano can be changed by decreasing the length of the strings and increasing the tension of the strings.

5. Since sound travels fastest in solids, one can hear two sounds. The fi rst sound reaching our ears is the one travelling through the metal rails and the one that comes later is the sound travelling through air.

6. Speed of sound, in air = 343 m/s at 20°C

Water = 1482 m/s

Steel = 5960 m/s

7. The speed of light is much faster than speed of sound. Speed of light being 3 × 108 m/s as compared to speed of sound in air being 343 m/s. Thus lightning is seen much before sound of thunder is heard.

8. Refer activity on page 96 from the textbook.

D. 1. Amplitude: It is the maximum displacement of the particles of a wave from its mean position. It is measured in meters.

2. Time period: It is defi ned as the time taken for one complete vibration to pass through a given point.

3. Echo: It is the refl ection of sound wave after striking a rigid surface such as a wall or a cliff situated beyond 16.5 m.

4. Wavelength: The distance between two successive crests or troughs in a transverse wave and distance between two successive compressions or two successive rarefactions in a longitudinal wave is called a wavelength. In other words it

is the length of one complete cycle of a wave.

5. Rarefaction: Rarefaction is an area of low pressure wherein the air particle are far apart in a longitudinal wave.

E. 1. Wavelength: The distance between two successive crests or troughs in a transverse wave and distance between two successive compressions or two successive rarefactions in a longitudinal wave is called a wavelength. In other words it is the length of one complete cycle of a wave.

Frequency: Number of waves passing through a point in one second is called frequency. It is measured in Hertz.

2. Sound waves: They need a material medium to travel.

The speed of sound waves in air is 330 m/s.

In air, sound waves are longitudinal.

Light waves: They can travel in vacuum.

The speed of light waves is 3 × 108 m/s.

Light waves are transverse waves.

3. Compressions and rarefactions are found in longitudinal waves in air.Compression is an area of high pressure where the air particles are close to each other whereas rarefaction is an area of low pressure where the air particles are far apart.

4. Amplitude: It is the maximum displacement of the particles of a wave from its mean position. It is measured in meters. Greater the amplitude, louder is the sound wave.

Frequency: Number of waves passing through a point in one second is called frequency. It is measured in Hertz.

5. Refl ectors of sound: Any smooth and hard surface like walls, rocks, pillars, wood, metal sheets and glass will refl ect sound waves. Absorbers of sound: Materials that are rough and heavy such as carpets, curtains, sofa sets, bed linen, etc., are good absorbers of sound waves.

5151

F. 1. v = 2 d/t,

v = 2 × 66/ 0.4 = 330 m/s

2. d = v x t,

d = 330 × 3 = 990 m

3. v = 2 d/t,

d = v x t/2,

d = 1430 × 1/2

d = 715 m

4. Frequency of pendulum A = Number of oscillations in 1 sec = 15/5 = 3 Hz

Frequency of pendulum B = Number of oscillations in 1 sec= 8/4 = 2 Hz

Therefore, pendulum A has higher frequency.

5. Time period = 1/frequency,

T = 1/10 = 0.1 sec

6. v = 2 d/t

d = v × t/2 = 1500 × 3/2

d = 2250 m

LEARNING ZONE


1. (a) 3 waves

(b) Wavelength is between two crests.

wave length

Time

Wav

e di

spla

cem

ent

(c) amplitude

Wav

e di

spla

cem

ent

Time

2. (a) Wave B is louder.

(b) Wave A has higher frequency.

3. (a) Yes.

(b) t = 2d / v,

= 2 × 20/330 = 0.12 seconds

The echo will reach the girl after 0.12 seconds.

4. The soldier in the submarine will hear the gun shot fi rst because the sound that travels through water to the submarine is faster, its speed being 1482 m/s as against the sound travelling through air with a speed of 343 m/s.

Think and answer

1. Speed of sound changes.

2. During rock concerts sound level is very high. Any sound which is above 90 dB, is harmful to the human body. Exposure to levels of sound beyond the permissible limit can cause health hazards such as irritability, nervousness, head-ache and even nervous breakdown.

3. Speed of light is much faster than speed of sound in air. Speed of light is 3 × 108 m/s whereas speed of sound is 330 m/s, hence we lightning fi rst and hear the sound of thunder a little later.


WORKSHEET 1

1. a. Sound

b. longitudinal

c. 200

d. echo

2. a. F b. T c. F d. T

3. a. Frequency

b. Metal sheets

c. 1480 m/s

d. Sonar

5252

4. a. Speed of sound in different mediums depends on its elasticity and density.The greater the elasticity and lower the density of the medium, faster will be the sound.

b. Bats emit high frequency squeaks and then listen to the echo produced by the obstacles or insects in their path. The time taken by the echo to return gives them an estimate of the distance of the refl ecting source.

WORKSHEET 2

1. a. iii b. i c. iv d. iv

2. a. 100 m/s

b. Compression

c. Pitch

d. Refl ection

3. a. i. To hear an echo, the sound after refl ection from a rigid surface should reach the ear at least 0.1 sec after the original sound is heard.

ii. To hear the echo clearly, the refl ecting surface should be at a minimum distance of 16.5 m from the source of sound.

b. SONAR uses sound waves and has a transmitter and a detector to send and receive sound waves. A short sound signal is sent from the ship to the bottom of the sea with the help of a transmitter. After refl ection from the sea fl oor, the signal returns to the ship and is received by the detector. Knowing the speed of sound in sea water and the time taken to reach the bottom and return back, we can easily determine the depth of the sea and similarly shoals of fi sh.

c. Frequency = 120/24 = 5 Hz

Time period = 1/F, = 1/5

= 0.2 seconds

5353

Learning Objectives

Students will be able to: learn the concept of law of magnetism and test for a magnet

understand the concept of electromagnetism, electromagnet and its uses

understand and learn the concept of electric bell, electric current, electric cell and primary and secondary cells

understand what is electrical circuit, and what are open and closed circuits, and electric switch

understand the concept of simple electric circuit, resistors, good and bad conductors of electricity

7 Electricity and Magnetism

Warm-upStudents are shown magnets of different shapes such as a bar magnet, cylindrical magnet, circular magnet, horse-shoe magnet and a magnetic compass. Polarity is determined by bringing iron nails and an iron bar near each of these magnets. Repulsion is tested by bringing an ordinary iron bar fi rst near one end and then at the opposite end of a magnet. Hence one can determine whether an ordinary iron bar is a magnet or not.

Students are shown an electric bell, a motor, an old fan that has a motor inside, electronic gadgets and toys and the fact is stressed that all the above devices use magnets and electricity to function. Hence the word electromagnetism.


Concept Explanation

Law of Magnetism, Test for a Magnet, Electromagnetism, Electromagnet, Uses of Electromagnets– Read the related sections from the

textbook.

– Students are asked to bring an iron nail, a 1 metre long insulated copper wire, a6 V battery, a bar magnet, a toy car, paper clips, safety pins, etc.

– Make a coil of the wire tightly around the iron nail. Connect the terminals of the battery to the two ends of the wire coiled around the nail. Bring the electromagnet close to some paper clips, safety pins and iron fi lings. These immediately get attracted to the electromagnet made by you.

– Bring a bar magnet near one end of the electromagnet. It may be attracted.

5454

Reverse the end of the bar magnet and bring it close to the electromagnet again. This time there is repulsion. Thus, it can be proved that the electromagnet made by you has a north pole and a south pole.

– If you increase the number of turns of the copper wire, you will notice that it becomes a stronger magnet.

– Discuss with the students the uses of electromagnets.


Electric Bell, Electric Current, Electric Cell, Primary and Secondary Cells – Read the related sections from the

textbook.

– Take the students to the science lab of the school. Show them a secondary cell like a lead acid battery or alkaline batteries and ask them to compare these batteries to the dry cell you use in your torches, cameras, etc. List out the advantages of the secondary cells over a primary cell.



Electrical Circuit, Open and Closed Electric Circuit, Electric Switch, Simple Electric Circuits, Resistors, Good Conductors and Bad Conductors of Electricity– Read the related sections from the

textbook.

– Explain and defi ne the concept of electrical circuits to the students.

– One can make a simple circuit in series by attaching two bulbs to a battery and a switch.

– Observe the brightness of the bulbs.

– Next connect the bulbs in parallel and observe the brightness of the bulbs.

– Compare the utility of the two types of connections. Disconnect one of the bulbs in each case. You fi nd in series circuit the second bulb does not glow whereas in parallel circuit the second bulb continues to glow with the same brightness. Draw your own conclusions.

– Defi ne that resistors are devices or electrical components having resistance to the passage of an electric current. A resistor in an electric circuit limits or regulates the fl ow of electricity.

– Differentiate between good and bad conductors of electricity.






5555

Worksheet 1


a. The chemical solution in a cell is called a/an ______________.

b. A standard dry cell produces a voltage of ______________.

c. Household wiring is the best example of ______________ circuit.

d. ______________ is a sure test of magnetism.


a. Electric current is measured by a voltmeter.

b. The doorbell works on the heating effect of current.

c. Copper and silver are the best conductors of electricity.

d. Electrons are the carriers of charge and also called mobile electrons.


a. A device that shows resistance to the passage of electric ________________current

b. The Danish Physicist who discovered the relationship ________________between electricity and magnetism

c. A type of temporary magnet ________________

d. A cell that produces weak current ________________


a. How are parallel circuits, and parallel system of wiring more advantageous than series circuit and series wiring?

_____________________________________________________________________

_____________________________________________________________________

b. Draw a neat and labeled diagram of an electric bell and explain the use of the electromagnet shown in the diagram.

_____________________________________________________________________

_____________________________________________________________________

5656

Worksheet 2


a. A permanent magnet is made of

i. iron ii. steel iii. copper iv. Any of these

b. Charges always occur

i. singly ii. in a group iii. in pairs iv. separately

c. The human body is a good conductor of

i. charge ii. electricity iii. heat iv. All of these

2. Match the columns.

a. A dry cell i. Household wiring

b. Galvanometer ii. Free electrons

c. Parallel circuit iii. Can detect weak current

d. Copper iv. 1.5 V


a. Battery, Dry cell, Alkaline battery, Electric circuit, Acid battery

b. Electron, Gamma rays, Protons, Neutrons, Atom

4. Answer the questions:

a. What are the advantages of a secondary cell over a primary cell?

_____________________________________________________________________

_____________________________________________________________________

_____________________________________________________________________

b. State two uses of electromagnets.

_____________________________________________________________________

_____________________________________________________________________

_____________________________________________________________________

5757


PART 1

A. 1. (a) 2. (b) 3. (c) 4. (c)

5. (a) 6. (b) 7. (b) 8. (a)

B 1. Repulsion 2. magnetic

3. Metals 4. Current

5. electromagnet 6. chemical, electric

7. electrons 8. electromagnet

9. permanent 10. magnetic

C. 1. F 2. T 3. F 4. F

5. T 6. T 7. F 8. T

D 1. Iron 2. Repulsion

3. Electromagnetism 4. Conductors

5. Galvanometer 6. Lead acid battery

7. Potentiometer 8. Parallel

9. Battery 10. Open circuit

PART 2

A 1. Copper 2. Wood 3. Switch

4. Parallel circuit 5. Lead-acid battery

6. Nickel-cadmium cells or alkaline batteries

7. Ampere

B 1. If the switch is off, or the connection is broken or if there is an insulator in the path of current, the circuit is said to be broken or incomplete.

2. Electromagnets are used in cranes to pick up scrap and also used to separate magnetic and non-magnetic substances in scrapyard.

3. An electrolyte is a chemical in solution form or semi-solid paste which dissociates into positive and negative ions responsible for the passage of electric current.

4. A number of similar cells connected together form a battery. A battery is used when a strong current is needed.

5. A dry cell cell is a type of electric cell which has the electrolyte in the form of a

semi solid paste. In this case the electrolyte is a moist paste of ammonium chloride.Dry cells are cheap and convenient to use. It has a voltage of 1.5 V.

6. A switch is an on and off device for an electric current.

C 1. Metals such as copper have a large number of free electrons. It is these electrons that are responsible for the conduction of electricity. Such electrons are responsible for the conduction of electrons. These mobile electrons are called carriers of charge.

2. Conductors have a large number of free electrons moving across, transmitting electric charge. They allow electric current to pass through them. For example, copper, aluminium, iron, etc.

3. Electric bell: When the switch is on, an electric current fl ows through the electromagnet.

It attracts the soft iron strip. The hammer attached to the strip hits the gong, the bell rings. The connection with the screw is broken and the current stops fl owing. The electromagnet loses its magnetism, and the iron strip returns back to the screw. Once again the current starts fl owing, the electromagnet attracts the strip and the hammer strikes the gong. This continues till the switch is on and the bell continues to ring. (Refer Fig. 7.2 from the textbook).

4. Working of an dry cell: The chemical in a dry cell in the form of a solution or a semi

solid paste, is called an electrolyte. The positive and negative ions in the solution are responsible for the passage of electric current. This makes the electrical object work when connected to the cell. Here chemical energy of the electrolyte is converted into electrical energy. (Refer Fig. 7.4 from the textbook).

5858

5. Parallel circuit: In a parallel circuit, there is more than one path for the electrons to fl ow. Each light bulb receives current from the battery. All of them light up as if each of the bulbs was connected separately to the battery. Thus, if any one bulb fuses, the others continue to glow with the same brightness. However the battery will be used up there as quickly. (Refer Fig. 7.7 from the textbook).

6. Secondary cells can be recharged and reused. They have a longer life and can generate a strong current. They can be recharged and reused. They produce a voltage of 1.5 V. The electrolyte in the form of a semi solid paste can be used for portable devices and lasts longer.

D 1. Electromagnetism: Electromagnetism is a branch of physics which deals with electricity and magnetism and interaction between them. Electromagnetism is magnetic effect of electric current.

2. Current: It is the rate of fl ow of electric charge. The SI unit of current is Ampere.

3. Complete circuit: The circuit that allows current to fl ow through it so that the electrical appliance connected to it works is called a closed or complete circuit.

4. Electrolyte: An electrolyte is a chemical in solution form or semi-solid paste which dissociates into positive and negative ions responsible for the passage of electric current.

5. Battery: A number of similar cells connected together form a battery. A battery is used when a strong current is needed.

6. Electric switch: A switch is an on and off device for an electric current.

E 1. Primary cell: These cannot be reused and recharged.The chemical reaction in a primary cell is irreversible. It produces weak current.

Secondary cell: Secondary cells can be recharged and reused. They have a long life and can generate a strong current. The chemical reaction is reversible in a

secondary cell. These cells are used for portable devices and lasts longer.

2. Electromagnet: It is made of soft iron. The strength of an electromagnet can be increased when desired as in the case of a crane. The poles of an electromagnet can be reversed. It is a temporary magnet.

Permanent magnet: These are made of steel. Its magnetic strength cannot be changed. It has fi xed poles. Magnetism is permanent.

3. Open circuit: If the switch is off, or the connection is broken or if there is an insulator in the path of current, the circuit is said to be open or incomplete.

Closed circuit: The circuit that allows current to fl ow through it so that the electrical appliance connected to it works is called a closed or complete circuit.

4. Series circuit: When two or more bulbs are connected in series one after another, there is only one path for electrons to fl ow. Hence same current passes through each bulb. If one bulb fuses , the others do not glow. Two or three bulbs connected in series glow dim.

Parallel circuit: In a parallel circuit, there is more than one path for the electrons to fl ow. Each light bulb receives current from the battery. All of them light up as if each of the bulbs was connected separately to the battery. Thus, if any one bulb fuses,the others continue to glow with the same brightness. However the battery will be used up there as quickly.

5. Conductors: Conductors have a large number of free electrons moving across, transmitting electric charge. They allow electric current to pass through them easily. For example, copper, aluminium, iron, etc.

Insulators: Insulators have very few free electrons to transmit charge, hence they are also called bad conductors. For example, ebonite, fur, wood, distilled water, etc.

F 1. electric bulb 2. electric fuse 3. gold 4. wood

5959

Learning ZonePicture Based Questions

1. Switch Batt erySpring

Gong HammerElectromagnet

Soft iron armature

Working of an electric bell:

a. When you push the switch of the bell, an electric current fl ows through the electromagnet.

b. The electromagnet attracts the soft iron strip. The hammer attached to the strip then hits the gong, making it ring.

c. As the soft iron strip gets attached to the electromagnet, it does not touch the screw, and hence, the circuit is broken. This turns off the electromagnet and it can no longer attract the soft iron strip. The soft iron strip returns to its initial position and touches the screw. This results in the circuit being

completed and current starts fl owing again.

2. Drawing of an electric circuit, using symbols of battery, resistor, switch and bulb.

3. a. Arrange them in parallel

b. If one bulb fuses, the other bulb continues to glow with same brightness.

4. Electromagnet ‘B’ is stronger because it has more number of turns of the coil.

5. a. The cell is the source of power.

b. Sow in the diagram arrows and + and – sign.

+ –

Think and Answer1. Our body contains ions like sodium,

potassium, chloride ion in the water which makes up 75% of the human body, it tends to conduct electricity. This makes our body a good conductor of electricity.

2. Water being a good conductor can form a conducting layer and reach the person who is dousing the fi re. The person may get an electric shock or be electrocuted.

3. Wires used at home are insulated because people coming in contact with them can get an electric shock because they are good conductors of electricity.

Wires overhead are naked so that large amount of heat generated due to passage of current can dissipate the heat away.

4. a. The bulb will begin to glow dim.

b. The bulb will glow more brightly.

6060

A 1. (d) 2. (c) 3. (b) 4. (a) 5. (b)

B 1. Open circuit: In an open circuit the switch is in the off position and the current does not fl ow.

2. Rarefaction: The area along the length of a longitudinal wave where the air particles are far apart, creating a region of low pressure.

3. Electric switch: It is an on and off device for current in an electric circuit.

4. Echo: It is the refl ection of sound after it strikes a rigid surface like a wall, a rock, a mountain or any other solid barrier.

5. Convection: Convection currents occur in liquids and gases where the heated particles of the medium rise upwards creating a vacuum so that the heavier particles of the medium descend down to take its place. A continuous circulation of medium particles is maintained.

C. 1. (a) 2. (d) 3. (e) 4. (c) 5. (b)

D 1. Black surface 2. Hertz 3. Second

4. Electric circuit 5. Electric motor

E 1. Series circuit: When two or more bulbs are connected in series one after another, there is only one path for electrons to fl ow. Hence same current passes through each bulb. If one bulb fuses , the others do not glow. Two or three bulbs connected in series glow dim.

Parallel circuit: In a parallel circuit, there is more than one path for the electrons to fl ow. Each light bulb receives current from the battery. All of them light up as if each of the bulbs was connected separately to the battery. Thus, if any one bulb fuses, the others continue to glow with the same brightness. However the battery will be used up there as quickly.

2. Primary cell: These cannot be reused and recharged.The chemical reaction in a primary cell is irreversible. It produces

weak current.

Secondary cell: Secondary cells can be recharged and reused. They have a long life and can generate a strong current. The chemical reaction is reversible in a secondary cell. These cells are used for portable devices and lasts longer.

3. Compressions and rarefactions are found in longitudinal waves in air.Compression is an area of high pressure where the air particles are close to each other whereas rarefaction is an area of low pressure where the air particles are far apart.

4. Electromagnet: It is made of soft iron. The strength of an electromagnet can be increased when desired as in the case of a crane. The poles of an electromagnet Can be reversed. It is a temporary magnet.

Permanent magnet: These are made of steel. Its magnetic strength cannot be Changed. It has fi xed poles. Magnetism is permanent.

F. 1. F 2. T 3. T 4. F 5. F

G 1. The wheels of a horse cart are made of wood. An iron rim which is slightly smaller in siametere than the wooden wheel is heated till it expands and slides easily over the wooden wheel. Cold water is then poured over it so that it contracts and grips the wheel tightly.

2. Fire: It is a rapid chemical change in which heat and light are produced. Certain infl ammable substances have low ignition temperature. Wood, coal, kerosene and petrol etc. burn easily and are called infl ammable substances.

3. Two effects of heat are: Fire and change in temperature: When a body is heated its temperature rises and when it is cooled its temperature decreases.

4. Refl ectors of sound: Any smooth and hard surface like walls, rocks, pillars, wood,

Answers to Assessment 2

6161

metal sheets and glass will refl ect sound waves.

Absorbers of sound: Materials that are rough and heavy such as carpets, curtains, sofa sets, bed linen etc are good absorbers of sound waves.

5. An echo is the sound heard after its refl ection from a rigid surface, such as a cliff or hillside, a wall or any obstructing surface. The minimum distance of the refl ecting surface from the source of sound should be 16.5 m for an echo to be heard.

6. Electric current is rate of fl ow of charge. SI unit of current is Ampere.

7. A resistor is a device that limits the fl ow of current or controls the current fl owing in a circuit.

H. 1. Working of an Electric bell: When the switch is on, an electric current fl ows through the electromagnet. It attracts the soft iron strip. The hammer attached to the strip hits the gong, the bell rings. The connection with the screw is broken and the current stops fl owing. The electromagnet loses its magnetism, and the iron strip returns back to the screw. Once again the current starts fl owing, the electromagnet attracts the strip and the hammer strikes the gong. This continues till the switch is on and the bell continues to ring.

2. Sound is produced when an object vibrates. Humans produce sound due to the vibrations of air in the vocal cords. Musical instruments like the guitar produce sound because of vibrations of its strings.

Sound waves in air produce alternate areas

of compression and rarefaction c a l l e d longitudinal waves. Longitudinal waves travel along the direction of propagation of the wave particles and reach the ear of the listener to produce sound.

3. SONAR uses sound waves and has a transmitter and a detector to send and receive sound waves. A short sound signal is sent from the ship to the bottom of the sea with the help of a transmitter. After refl ection from the sea fl oor, the signal returns to the ship and is received by the detector. Knowing the speed of sound in sea water and the time taken to reach the bottom and return back, we can easily determine the depth of the sea and similarly shoals of fi sh.

4. T = 1/F = 1/256

T = 0.0034 seconds

5. A diagram showing the complete path that allows current to fl ow through it is called an electric circuit diagram.

I. 1. Zinc vessel is the negative electrode

2. The two electrodes in the cell.

3. Primary cell cannot be recharged and reused. Secondary cells can be recharged and reused.

4. Paste of ammonium chloride.

5. Lead acid battery.


WORKSHEET 1

1. a. electrolyte b. 1.5

c. parallel d. Repulsion

2. a. False b. False

c. True d. True

3. a. Resistor b. Hans Christian Orsted

c. Electromagnet d. Primary magnet

6262

4. a. In a parallel circuit, there is more than one path for the electrons to fl ow. Hence each light bulb will receive current from the battery. All of them light up as if each of the bulbs was connected separately to the battery. Thus, if any one bulb fuses, the others continue to glow with the same brightness. However the battery will be used up there as quickly.

b. Switch Batt erySpring


Soft iron armatureContact screw

The electromagnet in the bell attracts the armature so that the hammer can hit the gong repeatedly.

WORKSHEET 2

1. a. ii b. iii c. iv

2. a. iv b. iii c. i d. ii

3. a. Electric circuit

b. Gamma rays

4. a. Secondary cells can be recharged and reused. They have a long life and can generate a strong current. The chemical reaction is reversible in a secondary cell.These cells are used for portable devices and lasts longer.

b. The strength of an electromagnet can be increased when desired as in the case of a crane. The poles of an electromagnet can be reversed. It is a temporary magnet.

6363

Total marks: 50Time: 3 hours

Model Test Paper 2

Section AA. Fill in the blanks. [5]

1. The Celsius scale is divided into ______________ equal divisions.

2. The mode of transfer of heat that does not require a medium is known as ______________.

3. Sound is produced by ______________.

4. A/an ______________ is a sound heard after refl ection from a rigid surface.

5. ______________ is the magnetic effect of current.

B. Multiple choice questions. [5]

1. Sound travels fastest in,

a. solids b. liquids c. gas d. plasma

2. In the process of convection, heat travels

a. downwards b. upwards c. sideways d. in all different directions

3. In one second, a fl y can fl ap its wings back and forth

a. 20 times b. 120 times c. 200 times d. 220 times

4. Ebonite is a/an

a. insulator b. conductor c. semi-conductor d. none of these

5. Number of waves passing through a point in on second is called

a. amplitude b. time period c. wavelength d. frequency

C. State True or False. [5]

1. When a sound is produced, particles of the medium move from one end to the listener.

2. An electromagnet is made of steel.

3. Copper has a large number of free electrons.

4. All solids expand by the same amount when heated to the same rise of temperature.

5. A resistor is a device that can detect even a weak current

D. Name the following. [4]

1. The change of state from solid to gas directly without passing through liquid state.

2. Maximum displacement of a wave from its mean position.

3. An on and off device for current in an electric circuit.

4. Substances that catch fi re easily.

Section BA. Defi ne the following. [3]

1. Temperature

6464

2. Electrolyte

3. Wavelength

B. Short answer questions. [12]

1. Can two persons hear each other on the moon? Why.

2. What is the difference between parallel and series circuit.

3. What is thermal equilibrium?

C. Long answer questions: [16]

1. How can one use SONAR to locate shoals of fi sh or the depth of the ocean fl oor?

2. Name the given symbols and their function in an electric circuit.

a. –+ b.

3. Draw a neat labelled diagram of an electric bell and state the function of:

a. Armature b. Electromagnet

4. Numericals:

a. 68 °C into the Fahrenheit scale

b. A sailor in a submarine hears an echo of a gun shot 2 seconds after it was fi red from the port. Taking the speed of sound in water as 1430 m/s, calculate the distance of the port from the submarine.

6565

Answers to Model Test Paper 1

Section A

A 1. Mercury

2. Density

3. Potential energy

4. 43 km/h

5. Normal

B 1. (c) 2. (a) 3. (c) 4. (c)

5. (c)

C 1. True 2. False 3. True 4. False

5. True

D 1. Mass

2. Random motion

3. Muscular energy

4. Virtual image

Section B

A 1. Kinetic energy: The energy possessed by a body due to its position or state of rest is called kinetic energy.

2. Acceleration due to gravity: The pull of gravity on objects on the surface of the earth is called acceleration due to gravity.

3. Complementary colours: A pair of colours, one primary and the other secondary, which on mixing form white light are called compelementary colours.

B 1. A fan, a washing machine and mixer grinder.

2. Real image:

a. The image is inverted.

b. Can be formed on a screen.

c. Formed by actual meeting of the refl ected rays.

Virtual image:

a. The image is erect.

b. Cannot be formed on the screen.

c. Formed by producing the refl ected rays backwards.

3. a. The fl ower vase will appear black in green light. In green light the fl ower vase will absorb the green colour and refl ect none.

b. In blue light it will appear blue, since in blue light it can refl ect blue colour.

C 1. Coal, petroleum and natural gas are called fossil fuels. Fossil fuels store energy in the form of chemical energy which is used to move vehicles, used as domestic fuel and provide heat energy.

2. Ray diagram:

A BA Bi r

PO

I

(Object)

(Image)

Q

M M’

3. Motion of a screw driver is rectilinear as well as rotatory. A moving cycle, rectilinear as well as rotatory.

4. D = m/v

V = m/d, 45 / 4.5 = 10 cm3

6666

Answers to Model Test Paper 2Section A

A 1. 100

2. Radiation

3. Vibrations

4. An echo

5. Electromagnet

B 1. (a) 2. (c) 3. (c) 4. (a)

5. (d)

C 1. False 2. False 3. True 4. False

5. False

D 1. Sublimation

2. Amplitude

3. Switch

4. Infl ammable

Section B

A 1. Temperature: The degree of hotness or coldness of an object is called its temperature.

2. Electrolyte: In a cell the chemical solution that has both positive and negative ions that conduct electricity is called an electrolyte.

3. Wavelength: The distance between two successive crests or two successive troughs in a transverse wave is called wavelength. Whereas in a longitudinal wave it is the distance between two successive compressions or rarefactions.

B 1. People cannot hear each other on the moon since there is no atmosphere on the moon. Sound needs a material medium to propagate. It cannot travel in vacuum.

2. Series circuit: When two or more bulbs are connected in series one after another, there is only one path for electrons to fl ow. Hence same current passes through each

Bulb. If one bulb fuses , the others do not glow. Two or three bulbs connected in series glow dim.

Parallel circuit: In a parallel circuit, there is more than one path for the electrons to fl ow. Each light bulb receives current from the battery. All of them light up as if each of the bulbs was connected separately to the battery. Thus, if any one bulb fuses, the others continue to glow with the same brightness. However the battery will be used up there as quickly.

3. Heat fl ows from a body at a higher temperature to a lower temperature till both bodies attain equal temperature. This is a state of thermal equilibrium.

C 1. SONAR uses sound waves and has a transmitter and a detector to send and receive sound waves. A short sound signal is sent from the ship to the bottom of the sea with the help of a transmitter. After refl ection from the sea fl oor, the signal returns to the ship and is received by the detector. Knowing the speed of sound in sea water and the time taken to reach the bottom and return back, we can easily determine the depth of the sea and similarly shoals of fi sh.

2. Name the Symbol of

a. A cell

Function of a cell : An electric cell is a direct source of electric current. It converts chemical energy into electrical energy.

b.

Function of a switch: It switches on the current and switches off the current.

6767

3. Switch Batt erySpring


Soft iron armatureContact screw

Function of :

a. Armature: The armature is attracted by the electromagnet and the hammer strikes the gong, so the bell rings.

b. Electromagnet: It attracts the soft iron

strip, the bell rings. When the circuit is broken, the electromagnet loses its magnetism, the soft iron strip returns back to the screw to complete the circuit once again, and the electromagnet attracts the armature again to ring the bell. This continues as long as the switch is pushed in the on position.

4. a. °C = (°F – 32) 59

(68 – 32) 59

= 20 °C

b. v = dt, d = v × t

∴ d = 1430 × 8

= 11440 m = 11.440 km

6868

NOTES.............................................................................................................................................................................................

.............................................................................................................................................................................................

.............................................................................................................................................................................................

.............................................................................................................................................................................................

.............................................................................................................................................................................................

.............................................................................................................................................................................................

.............................................................................................................................................................................................

.............................................................................................................................................................................................

.............................................................................................................................................................................................

.............................................................................................................................................................................................

.............................................................................................................................................................................................

.............................................................................................................................................................................................

.............................................................................................................................................................................................

.............................................................................................................................................................................................

.............................................................................................................................................................................................

.............................................................................................................................................................................................

.............................................................................................................................................................................................

.............................................................................................................................................................................................

.............................................................................................................................................................................................

Date post:	03-Sep-2020
Category:	Documents
Upload:	others
View:	163 times
Download:	25 times

7 The Physics Science Orbit - SARASWATI HOUSE Material... · 2018. 7. 3. · 7. Density is mass per...

Documents