2012

Secondary Three Physics

THE REPUBLISHED ED.

Lim Ting Jie

VS Class of 2011

TOPIC 1: MEASUREMENT OF PHYSICAL QUANTITIES

1. SUB-MULTIPLES AND MULTIPLES OF S.I. UNITS

p pico -12 da deca 1

n nano -9 h hexa 2

µ micro -6 k kilo 3

m milli -3 M mega 6

c centi -2 G giga 9

d deci -1 T tera 12

2. PRECISION OF INSTRUMENTS USED FOR MEASUREMENT

Metre rule 0.1cm / 1mm

Vernier calipers 0.01cm / 0.1mm

Micrometer screw gauge 0.001cm / 0.01mm

3. MEASURING TIME WITH A PENDULUM

Period of pendulum refers to the time taken for the bob to complete a full oscillation.

The period of pendulum depends on:

the length of the pendulum

the acceleration due to gravity

Precautions:

pendulum string must be taut

the angle of swing must be less than 10º

TOPIC 2: MASS, WEIGHT AND DENSITY

4. MASS AND WEIGHT

MASS WEIGHT

The amount of substance in a body The effect of a gravitational field on a mass

Measured in kg Measured in N

Constant; Cannot be changed Varies depending on location

Measured by beam balance or electronic

balance

Measured by spring balance (compression)

Has only magnitude but no direction (scalar) Has both magnitude or direction (vector)

5. INERTIA

Refers to the reluctance of an object to start moving if it is stationary/stop moving if it is

moving in the first instance.

Any object with mass has inertia and inertia is only dependent on mass.

A force is needed to overcome inertia. The bigger the mass the larger force required to

overcome the inertia.

6. GRAVITATIONAL FIELD

Refers to the region in which a mass experiences a force due to gravitational attraction.

Force is strongest on Earth‟s surface and weakest as we go further away.

7. GRAVITATIONAL FIELD STRENGTH

Expressed as g

Refers to the gravitational force acting on an object (the weight) per unit mass

Weight (W) = Mass x Gravitational force (mg)

S.I. unit : N kg-1 (also kg ms-2)

8. DENSITY

Expressed as

Refers to the mass per unit volume

S.I. unit: kg m-3

9. WHY SHOULD WE MEASURE AN OBJECT AT THREE DIFFERENT POSITIONS?

The diameter of the ball bearing or the height of the plank of wood differs slightly at

different parts of the ball.

This is to minimise errors that may be caused due to the non-uniformity of the ball / plank.

TOPIC 3.1: OPTICS (PART 1)

1. LIGHT RAYS

The paths along which light travels are called rays. A bundle of rays is called a beam.

There are three types of beams:

Parallel

Converging

Diverging

When light is struck on an object:

Absorbed

Reflection

Transmitted (e.g. refraction)

Ray diagram:

2. LAWS OF REFLECTION

The angle of incidence is equal to the angle of reflection.

The incident ray, reflected ray and the normal all lie on the same plane.

3. FEATURES OF A PLANE MIRROR IMAGE

V - Virtual

S - Size (Image is the same size as the object)

F - Far (Image as far away from the mirror as the object is from the mirror)

L - Laterally inverted

U - Upright

4. IMAGES SEEN IN MULTIPLE SUBTENDED MIRRORS

When subtended angle = 90º

Number of images = (360/90) - 1

= 3

5. REFRACTION OF LIGHT

Refers to the change in direction of bending of light when it passes from one medium to

another medium of different optical densities due to the change in speed of light.

6. LAWS OF REFRACTION

Incident ray, refracted ray and normal at point of incidence lie in the same plane.

For two given media, the ratio of sin i and sin r is a constant known as a refractive index.

7. REFRACTIVE INDEX

The main definition of the refractive index of a medium is that it refers to the constant

ratio of the speed of light in vacuum and the speed of light in the medium.

Refractive indices: Air (1), Ice (1.3), Water (1.33), Glass and Perspex (1.5), Diamond (2.4)

The refractive index can be defined in three ways:

*speed of light in vacuum is 3 x 108

8. CRITICAL ANGLE

Critical angle is the angle of incidence in an optically denser medium when the angle of

refraction in air is 90o. When critical angle is greater, total internal refraction occurs.

Formula for finding critical angle using the refractive index: c = sin-1 (1 / n)

9. OPTICAL FIBRE

Optical fibre is a elastic tube made of glass.

It is more advantageous than copper wires for carry telephone communications as it is

generally cheaper, has less signal loss, carry more data and at a faster rate.

10. COMPONENTS OF A CONVERGING LENS

Principal axis - line joining the centers of curvature of the two surfaces

Optical centre - centre of the lens

Principal focus - point where parallel rays of light converge after passing through the lens

i. When the rays enter the lens at 90º, the principal focus will lie on the

principal axis. This focal point is used to solve problems on images of a

converging lens.

ii. The principal focus may change depending on the angle the rays enter the lens.

Focal length - distance between the optical center and the principal focus

What happens when the bottom half or top half of the lens is covered by an opaque material?

The intensity of the image is decreased by half. The image location remains unchanged.

11. RAY DIAGRAMS OF CONVERGING LENS

Object location Image location Image properties Functions

u = v = f DIR Telescope

u > 2f 2f > v > f DIR Camera, Eye

u = 2f v = 2f SIR Photocopier

2f > u > f v > 2f MIR Projector

u = f v = MUV Spotlight

u < f -f > v > -2f MUV Magnifying glass, Spectacles

12. DRAWING RAY DIAGRAMS OF CONVERGING LENS WITH A SCALE

Principal axis scale (diagram scale : original scale)

i. Horizontal length as x-axis

Object scale (diagram scale : original scale)

i. Vertical length as y-axis

i.

TOPIC 4: KINEMATICS

1. GRAPHS

Increasing acceleration and deceleration

gradient firstly heads then goes either or

Decreasing acceleration and deceleration

gradient firstly goes either or then heads

2. EQUATIONS OF CONSTANT ACCELERATION

a =

By equating the formula:

v = u + at (Velocity and Time)

s = ut + ½ at2 (Displacement and Time)

v2 = u2 + 2as (Displacement and Velocity)

On graph:

Average velocity = ½ (v + u)

Total distance = ½ (v + u) (t)

3. EQUATION OF VELOCITY

v =

4. CONCEPTS IN RELATION TO TERMINAL VELOCITY

When an object falls from the sky on Earth, the object undergoes a constant

acceleration of 10 m s-2 if air resistance is ignored.

However, when air resistance is taken into account, acceleration decreases from 10 m s-

2 to 0 m s-2.

This is because air resistance opposes the motion of the object. Also, air

resistance increases with velocity.

Acceleration/m s-2 Velocity/m s-1 Air resistance/N Resultant force/N Weight of

object/N

10 0 0 W - 0 = W W

0 < a < 10 0 < v < terminal

velocity

0 < r < W 0 > r > W W

0 Constant W W - W = 0 W

TOPIC 5: FORCES AND DYNAMICS

1. FORCES

A force is a push or a pull that acts on a body.

Forces can do the following:

Distortion in body

Change in direction

Change velocity

2. LAWS OF MOTION

An object will remain at rest or continue in its motion with constant velocity unless

acted on by a net external force.

When a resultant force acts on an object of constant mass, the object will accelerate

and move in the direction of the resultant force. The resultant force is the product of

the mass and acceleration of the object.

Fnet = ma

The unit of resultant force is Newton. One Newton refers to the force which

produces an acceleration of 1 m s-2 when it is applied to a mass of 1 kg.

o Similarly, two Newtons produce an acceleration of 2 m s-2 on a 1 kg mass

and an acceleration of 4 m s-2 to a 0.5 kg mass.

Net force refers to the vector sum of forces acting on the body in all

directions.

3. FREE BODY DIAGRAMS

Without air resistance With air resistance Object on

the ground

Object pushed

on the ground Object thrust

upwards

Object

released high

up

Object

thrust

upwards

Object

released high

up

T

W

W

T

R W

R

W

+F

W +Contact force

+F *f F

W *Friction

REVISION: FORMULAS

Semester 1

Standard

Weight Mass x Gravitational force

Density Mass ÷ Volume

Speed/Velocity Distance ÷ Time

Acceleration Change in speed ÷ Time

Equations for

acceleration

v = u + at

s = ut + ½ at2

v2 = u2 + 2as

Resultant force Mass x Acceleration

Identification

Images in a given

number of mirrors

Optical density

Semester 2

Standard

Moment Force OR tension x Perpendicular distance F d

Work done Force x Distance travelled Fd

Kinetic energy ½ Mass x Velocity2 ½mv2

Gravitational energy Mass x Gravitational force x Height mgh

Efficiency Energy output ÷ Energy Input x 100%

Power Work done OR Energy converted ÷ Time taken

Pressure Force ÷ Area in contact F/a

Water pressure Vertical height of water x Density x Gravitational force hρg

Identification

*Atmospheric pressure 1.013 x 105 Pa 760 mm Hg 76 cm Hg 0.76 m Hg 1 atmosphere

Density of mercury 13.6 x 103 kg m-3

Moments about a point Sum of clockwise moments = Sum of anti-clockwise moments Energy changes in speed

and height GPEA + KEA = GPEB + KEB

Total work done Work done to increase speed (which is uo - vo) + against gravity +

against friction

Pressure difference PA = PB (may be converted to FA/AA = FB/AB )

To be learnt

Gas Laws

Centigrade scale equation

Thermocouple measurements

Heat capacity

Specific heat capacity

Latent heat of fusion

Latent heat of vapourisation

Law of Conservation of Energy (Heat)

TOPIC 6: TURNING EFFECTS OF FORCES

1. DEFINITION OF MOMENTS, CENTRE OF GRAVITY AND STABILITY

The moment of a force is the product of:

the amount of force

the perpendicular distance from the pivot to the line of action of force

The centre of gravity of an object is defined as the point through which its whole weight

appears to act for any orientation of the object.

Stability refers to the ability of an object to return to its original position after it has

been tilted slightly.

2. ANSWERING QUESTIONS ON MOMENTS

By principle of moments, taking moments about Point A, Sum of clockwise moments = Sum

of anti-clockwise moments. W1 x d1 = W2 x d2.

3. CASES OF EQUILIBRIUM

Stable equilibrium

When tilted, centre of gravity rises then falls again

Unstable equilibrium

When tilted, centre of gravity falls and continues to fall further

Usually turns to the neutral equilibrium position

Neutral equilibrium

When tilted, COG remains at the same level above the surface supporting it.

Hence stability is increases only when

Centre of gravity decreases

Base area increases

An item comes to a high stability or to rest when the fulcrum and centre of gravity are

directly above or below each other (depending on scenario).

TOPIC 7: SCALARS AND VECTORS

1. SCALARS AND VECTORS

A scalar quantity has only magnitude while a vector quantity has both magnitude and

direction.

2. VECTOR DIAGRAM DRAWING

Parallelogram method (to find a resultant force when given two forces towards a similar

range of directions)

3000 N

2500 N

N

4550 N 40°

9°

30°

Tip-to-tail method (to find a third force that equates to an equilibrium, or to find the

velocity at an angle when affected by external factor)

TOPIC 8: ENERGY, WORK AND POWER

1. WORK DONE

Work done is the product of the force on a body and the distance it moves in the direction

of the force. Work done = (F)(d)

No work is done with no motion is produced or the motion moves perpendicularly to the

direction of the force.

Work is not moment.

2. PRINCIPLE OF CONSERVATION OF ENERGY

Energy can neither be created nor destroyed, but can be converted from one form or

another or transferred from one body to another, while total amount of energy remains

constant.

In a pendulum bob:

o Air resistance (causes bob to not reach its original height)

o Friction between the fulcrum and the string (causes bob to not reach its original

height)

o Tension of string (does not affect the bob‟s height, as it is perpendicular to the

direction of motion)

3. SAMPLE QUESTIONS

a) Total work done

(i)

(ii)

1 2

20 m 5 m 2 kg

Constant

speed

If frictional force (f) = 10 N, what is the force

used to push the box up the slope to the end?

Total work done = Work done to increase speed

+ against gravity + against friction

(F)(20) = (0) + (mgh) + (fd)

= (0) + (2)(10)(5) + (10)(20)

F = 5 + 10

= 15 N

2 kg

5 m 20 m

If frictional force = 10 N, and start point and end point speeds are 10 ms-1 and 1 ms-1

respectively, what is the force used to push the box up the slope to the end?

(F)(20) = (½ mu2 - ½ mv2) + (mgh) + (Fd)

= [(½ )(2)(10)2 - ½ (2)(1)2)] + (2)(10)(5) + (10)(20)

F ≈ 399.33 ÷ 20

= 19.97 N

10 ms-1

1 ms-1

b) Roller coaster ride on a frictionless track for calculation of kinetic and gravitational

potential energy. (Courtesy of VS Physics Dept.) Assume speed at C and E are equal.

Speed at B and D are 0 ms-1.

Try working them out yourself first, without looking at the answers:

(i) Calculate work done from A to B

(ii) Calculate speed at C

(iii) Calculate speed at D

(iv) Calculate the total circumference of the loop.

Answers:

(i) Calculate work done from A to B (ii) Calculate speed at C

Work done = mgh

= (650)(10)(62.5)

= 406250 J

1. GPEB + KEB = GPEC + KEC

2. (GPEB - GPEC) + KEB = KEC

3. (650)(10)(62.5+30) + 0 = KEC

4. 601250 = ½ mv2

= ½ (650)(v)2

5. v = √1850

≈ 43.0 ms-1

(iii) Calculate speed at D (iv) Calculate the total circumference of the loop

1. GPEC + KEC = GPED + KED

2. (GPED - GPEC) + KED = KEC

3. (650)(10)(62.5-50) + 0 = KEC

4. 81250 = ½ mv2

= ½ (65)(v)2

5. v = √250

≈ 15.8 ms-1

1. GPEC + KEC = GPEE + KEE = GPEF + KEF

2. GPEC + KEC = GPEF + KEF

3. 0 + 601250 = (650)(10)(h) + (½ )(650)(15.2)2

4. 925 = 10 h + 115.52

5. 10 h = 809.48

6. h = 80.948 m

7. Circumference = 80.948π

≈ 254 m

c) A really useful fact!

If GPEX + KEX = GPEY + KEY, where speed at X is zero and Y is at level ground.

GPEX + 0 = 0 + KEY

GPEX = KEY

mgh = ½ mv2

2gh = v2

TOPIC 9: PRESSURE

1. PRESSURE AND ATOMOSPHERIC PRESSURE

Pressure is defined as the normal force per unit area.

Atmospheric pressure is caused by the molecular bombardment of energetic molecules.

Internal pressure of the fluids in the human body is approximately equal to atmospheric

pressure or 1 atmosphere. (1.013 x 105 Pa or 760 mm Hg)

B A

C

D

E vF = 15.2 ms-1

62.5 m

30 m 50 m

Mass of

roller

coaster =

650kg

F

h

2. USES OF ATMOSPHERIC PRESSURE (GOOD TO KNOW)

Using a syringe

o To draw liquid into the syringe, its piston is drawn upwards.

o This decreases the pressure within the cylinder.

o Atmospheric pressure acting on the surface of the liquid drives and forces the

liquid into the cylinder through the nozzle.

Rubber sucker

o To put the sucker in place, it is pressed in onto a flat surface to force out the air

within to create a partial vacuum.

o The greater atmospheric pressure acts on it to keep it in place on the flat surface.

Sucking through a straw

o The action of sucking increases the air volume in our lungs, thus reducing air

pressure in the lungs and mouth.

o Atmospheric pressure acting on the surface of the liquid is higher than the

pressure in the mouth.

o This forces the liquid to rise through the straw.

3. EXAMPLES OF USE OF ATMOSPHERIC PRESSURE

(a) Hydraulic systems

As both water levels are at the same

depth, PressureX = PressureY.

FX

= FY

AX AY

(FX)(AY) = (FY)(AX)

(FX)(dX) = (FY)(dY)

(b) Gas pressure

(c) Pressure by depth

Refer to diagram on the right.

FX

FY

AX AY

A B

PA = PB

=

Gas pressure = PATM + hρg

(Where h is height of liquid above B)

h

h1

h2

P = PATM

P = PATM + h1ρg

P = PATM + h1ρg + h2ρg

proof of hρg‟s units = m x kg m-3 x 10 ms-1

= m-2 x kg x 10 ms-1

= N m-2

TOPIC 10: KINETIC MODEL OF MATTER

1. PROPERTIES OF MATTER

Solid Liquid Gas

Volume 1Fixed 3Fixed 5Not fixed

Shape 1Fixed 3Not fixed 5Not fixed

Compressibility 2No No 6Yes

Density 2High 4High 6Low

Others Usually hard and rigid 4Tend to form droplets -

Reasons by

Kinetic

particle theory

1. Vibrate in fixed

positions

1. Held together by

strong intermolecular

bonds

2. Close together,

occupying minimum

space

Arranged in fixed

pattern

Arranged in an irregular

pattern

Free to move within

clusters (#not in

Chemistry)

Slide past one another

3. Slightly further apart than

solids

4. Relatively strong forces of

attraction

5. Move about in

continuous random

motion at high

speeds

6. Far apart from each

other

6. Occupy any

available space

2. BROWNIAN MOTION

It is a phenomena whereby small particles suspended in a liquid or gas

tend to move in random paths through the liquid or gas

even if it is calm

(a) Why does a smoke particle move in a constant random erratic motion?

It is being bombarded continuously by air molecules moving in a continuous random

manner, hence moving in an erratic manner.

The direction of each push of an air molecule changes the direction of the smoke

particle at random.

(b) Why doesn’t an empty drink can crush although atmospheric pressure exerts on it?

Randomly moving gas molecules collide with one another and with the inner walls of the

container containing the gas.

Collisions with the walls produce forces. Pressure is hence exerted as force is acted on

the inner surface area of the container.

3. GAS LAWS (T in K = θ in °C + 273)

Boyle’s Charles’ Gay-Lussac’s

Law

For a fixed mass of gas

at constant temperature,

the pressure is inversely

proportional to its

volume.

For a fixed amount of gas

at a fixed pressure, the

volume is proportional to

the Kelvin temperature

At constant volume, the

pressure of a gas is directly

proportional to the Kelvin

temperature.

Boyle’s Charles’ Gay-Lussac’s

Factors Pressure and Volume

(Temperature constant)

Temperature (K) and

Volume (Pressure fixed)

Pressure and Temperature (K)

(Volume constant)

Formula p1V1 = p2V2 V1

= V2

P1

= P2

T1 T2 T1 T2

Explanation

Volume is decreased.

Gas molecules will

collide with the walls

more frequently.

The average force per

unit area increases.

Pressure is increased.

Temperature increases.

The gas molecules gain more kinetic energy.

The molecules collide with the walls of the container

more frequently.

With a greater force.

The walls will expand until the

pressure of the gas in the container

balances the atmospheric pressure

(provided the walls can move). Volume is increased.

Greater

force per

unit area.

Pressure is

increased.

Combined

Gas Law

P1V1 =

P2V2

T1 T2

TOPIC 11: TEMPERATURE

1. HEAT AND TEMPERATURE

Temperature Heat

A measure of the degree of

„hotness‟ and „coldness‟

Used to determine the flow of

heat energy between two

objects in contact

The amount of thermal energy

that flows from a hotter object

to a colder object

2. CALIBRATING A THERMOMETER

a) Put thermometer in melting ice and mark on the thermometer the lower fixed point of 0 °C.

b) Put thermometer in steam and mark on the thermometer the upper fixed point of 100 °C.

c) Divide the the interval between the fixed point into 100 equal parts, each a degree Celsius.

3. GENERAL CENTIGRADE SCALE EQUATION

θ = Xθ - X0

x 100 °C X100 - X0

X refers to resistance or pressure

X may be substituted with l as the length of mercury thread

4. DESCRIPTIONS OF THE METHODS OF MEASURING TEMPERATURE

Mercury Alcohol Thermocouple

Glass

Does not stick to

glass, visible

meniscus

Sticks to glass, needs to

be dyed No glass is required

Reaction Reacts quickly to

temperature changes Slow to react

Has quick response, suitable to

measure temperature with rapid

changes

Mercury Alcohol Thermocouple

Expansion Uniform expansion Non-uniform expansion No expansion required

Range Good upper limit

(-39 °C to 357 °C)

Good lower limit

(-115 °C to 78 °C)

Wide range of temperatures,

dependent on type of metals used

(-200 °C to 1500 °C)

Cost Expensive Cheap Expensive

Others Poisonous Safe Small junction, can measure

temperature at a specific point (adv.)

5. ADAPTIONS OF A LABORATORY THERMOMETER AND CLINICAL THERMOMETER

Characteristics Sensitivity Responsiveness Range

Definition

change in length of

mercury thread per unit

temperature change

how fast the thermometer

responds to a change in

temperature

range of temperature

that the thermometer can

measure

Factors (that

can increase

the above

characteristics)

Low range of

thermometer Smaller volume of liquid Low sensitivity

Large bulb

Thinner bulb wall Length of stem Thin bore

Adaptations Narrow diameter Thin glass bulb Long

Round oval glass stem to act as a magnifying glass and improve sensitivity

Clinical Short temperature range Constriction in capillary tube

Adaptations

35 °C to 42 °C to save glass

material needed for the

stem

To prevent the mercury column from falling back

immediately after measurement, ensuring an accurate

measurement

TOPIC 12: HEAT CAPACITY

1. HEAT CAPACITY AND SPECIFIC HEAT CAPACITY

Heat capacity is the amount of heat required to raise a body by 1 K or 1 °C.

The SI unit is JK-1.

Specific heat capacity is the amount of heat required to raise the temperature of 1 kg of a

body by 1 K or 1 °C. The SI unit is Jkg-1K-1.

C = Q

Q = C ∆θ

Q = Pt ∆θ

c = Q

Q = m c ∆θ

m∆θ

Measuring

temperature with a

thermocouple

2. INTERNAL ENERGY

Refers to the kinetic and potential energy of particles in a body due to the movement and

arrangement of the particles.

3. MELTING AND SOLIDIFICATION, MELTING AND BOILING POINTS

Why is there no temperature change in the process?

Melting Boiling Solidification

Heat energy absorbed by ice is

used to do work in breaking the

intermolecular bonds between

the molecules.

Heat is absorbed by the liquid

to do work in breaking the

intermolecular forces between

the liquid molecules.

Heat energy is released as the

intermolecular bonds are formed

when the molecules come together

to form a sold.

Melting points decrease and boiling points increase when:

External pressure increases

Impurities are added

Example

a) Air pressure is increased to 2 atmosphere in a pressure cooker.

b) The cooker has an airtight lid except for a small hole at the top

c) Weights are put on top of this hole so that the inner air pressure

is more than atmospheric pressure.

d) Boiling point of water is increased and cooking time is reduced.

4. LATENT HEAT OF FUSION AND ENERGY NEEDED FOR OVERALL STATE CHANGES

Latent heat of fusion of a substance is

the heat needed to change it from the

solid state to the liquid state or vice

versa, without a temperature change.

Latent heat of vapourisation of a

substance is the heat needed to

change it from the liquid state to

the gaseous state or vice versa,

without a temperature change. Q = Pt

QF = mlF (where lF is the specific latent heat of

fusion in Jkg-1 and m is mass in kg)

QV = mlV (where lV is the specific latent heat

of vapourisation in Jkg-1 and m is

mass in kg)

Temperature graph of 0.2 kg water

If:

Latent heat of fusion of substance = 3.4 x 105 Jkg-1

Latent heat of vapourisation of substance = 2.2 x 106 Jkg-1

Specific heat capacity of water = 4200 Jkg-1°C -1

Total energy needed to convert substance from solid to gas

= Q + QF + Q + QV

= mc∆θ + mlF + mc∆θ + mlV

= (0.2)(4200)(40) + (0.2)(340000) + (0.2)(4200)(100) +

(0.2)(2200000)

= 625600 J

≈ 626 kJ

5. LAW OF CONSERVATION OF HEAT ENERGY

Total heat lost by hot substances = Total heat gained by cold substances

(mc∆θ)hot substance = (mc∆θ)cold substance

6. EVAPORATION

At any temperature, the molecules of liquid are in continuous random motion with different

speeds.

Some more energetic molecules near to the surface of the liquid have enough energy to

overcome the attractive forces of other molecules and escape.

They evaporate from the liquid to form a vapour.

Factors affecting rate of evaporation

Temperature High temperature = High rate

Area of exposed surface High area = High rate

Humidity of surrounding air High humidity = Low rate

Pressure High pressure = Low rate

Boiling point of liquid High boiling point = Low rate

^Movement of air above surface of liquid High movement = High rate

^Moving air removes molecules of the liquid as soon as they escape from the surface, increasing rate

of evaporation

TOPIC 13: TRANSFER OF THERMAL ENERGY

1. CONDUCTION, CONVECTION AND RADIATION

Conduction is the process by which heat is transmitted through a medium from one particle to another.

1) Why does conduction take place?

When a substance is heated at an end, particles at one

end gain energy and vibrate on the spot.

They collide with their neighbouring particles, passing

kinetic energy to them.

In this way, heat energy is passed along the substance

to surrounding substances in contact by the vibrating

particles.

2) Why is conduction of heat better in

solids than in liquids and gases?

In solids, the particles are closer together than in

liquids or gases.

Therefore kinetic energy can be transferred more

quickly.

3) Why is conduction of heat in metals

better than in non-metals?

There are „free‟ electrons in metals.

When heated, the „free‟ electrons can travel in spaces

between the particles before colliding with other

electrons, thus transferring energy to them.

Convection-transfer of thermal energy by means of heated particles by currents in gas or liquid.

1) How does the convection current

work in liquids? (due to

differences in density)

When a liquid is heated, it expands, becomes less dense

and floats upwards.

The cold and denser liquid moves down to replace it. This

in turn gets heated up.

2) Why can‟t convection occur in

solids?

Convection involves the bulk movement of fluids which

carry heat with them.

Solids cannot cause convection as heat can only be

transferred from one molecule to another.

The molecules are unable to flow around themselves.

3) Why do we feel a sea breeze at a

beach in the day?

During the day, the land is warmer than the sea. This is

because the specific heat capacity of land is lower than

that of the sea.

The hotter air above the land is less dense and rises.

Cooler air from the sea moves inland to take its place.

A convection current is formed and sea breeze is

obtained.

Radiation is a method of heat transfer by the continual emission of infrared waves from body surfaces and is transmitted without the aid of a material medium.

1. How does radiation work?

Any hot object will emit infrared waves.

When these waves reach another object, the waves are

transformed into heat.

This heat energy is then absorbed by the object.

2. What is rate of radiation dependent on? The higher the temperature of an

object, the faster the rate of radiation.

Colour of surface (explained on the left)

Total surface area

Dark surfaces Bright surfaces

Radiates best Radiates worst

Absorbs best Absorbs worst

Reflects worst Reflect best

3. FOOD PACKAGES

Adaptation Advantages Reasons

Mostly made of

styrofoam Conduction is reduced

This is due to the presence of many air

pockets

Air is a poor conductor of heat.

Covered with a lid Convection is reduced

Convection currents are unable to be set up due

to the presence of the lid compressing the

contents into a closely packed arrangement.

4. VACUUM FLASKS

Adaptation Advantages Reasons

Plastic stopper

Conduction and

Convection is reduced

Plastic is a poor conductor of heat.

With a stopper, a convection current is

being prevented from set up.

Vacuum between the glass walls

As vacuum is unable to conduct and

cause convection of heat, the amount of

heat medium is decreased.

Silvered glass walls Radiation is reduced

The shiny and smooth surface is a

poor emitter and absorber of heat.

It is able to reflect heat back to

the container very well.

Air trapped above contents Conduction is reduced Air is a poor conductor of heat.

-Nil Sine Labore-

# Term Definition Related Formulas

1 Inertia Reluctance of an object to start moving if it is stationary or

stop moving if it is moving in the first instance I α m

2 Mass Scalar quantity measuring amount of matter in an object W = mg

3 Weight Vector quantity measuring force of attraction on an object‟s

mass due to gravity W = mg

4 Gravitational

field strength The amount of gravity acting on an object per unit mass W = mg

5 Period Time taken for a pendulum bob to complete 1 full oscillation T = 2π √Length ÷ √g

6 Laws of

reflection

Angle of incidence is equal to angle of reflection. The

incident and refracted rays and the normal at point of

incidence all lie in the same plane

∠i = ∠r

7 Images on

mirrors

Image on mirror is virtual, same size as object, as far

away to the mirror as the object, laterally inverted, upright Ж Image “has the VS FLU”

Number of images on two subtended mirrors can be

calculated by measuring the subtending angle x° Images =

360 - x

x

8 Refraction

Bending of light rays due to change in speed of light when it

passes from a medium to another medium of different

optical densities

nd

= sin ∠i

= u

= rd

9

Laws of

refraction and

refractive

index

Incident and refracted rays and the normal at point of

incidence all lie in the same plane. For two given media in

which one is air, the ratio of the angle of incidence and

angle of refraction is a constant known as the refractive index

nld sin ∠r v ad

10 Critical angle

Angle of incidence in the denser medium when the angle of

refraction in the less dense medium is 90° (and a weak

reflected ray is produced)

∠c = sin-1 nld

nd

11 Total internal

reflection

Reflection of light rays within the denser medium when the

angle of incidence in the denser medium is more than the

critical angle

∠tir > c

12 Principal axis Line that joins the centers of the curvature of a lens

13 Principal focus Point in which parallel rays of light converge after they pass through the a convex lens

14 Focal length Distance between the principal focus or optical centre of the lens

15 Magnification The ratio of height of image to height of object or dist.

from image to lens to distance of object from lens M = I/O

16 Acceleration Change in velocity per unit time a = (v-u) ÷ t [s absent]

17 Displacement Distance travelled in a specific direction v2 = u2 + 2as [t absent]

18 Velocity Change in displacement per unit time s = ut + ½ at2 [v absent]

19 First law of

motion

An object will remain at rest or continue moving at constant

velocity unless acted on by a net external force Fnet = ma

20 Second law of

motion

When acted on by a net external force, an object of

constant mass will accelerate & move in the direction of force

21 Net force Total sum of all vector forces acted on object in all directions. Tension and weight are forces

22 Terminal

velocity

Maximum velocity of an object experiencing free fall in which air resistance is equal to weight &

acceleration is zero

23

Principle of

Conservation

of Energy

Energy cannot be created nor destroyed and can only be converted from one form to another or

transferred from one body to another, while total amount of energy remains constant

24 Moment Product of force applied and the perpendicular distance

from the pivot to the line of action of force M = F d

25 Principle of

moments

In equilibrium, the sum of clockwise moments about a pivot is

equal to the sum of anticlockwise moments about the same pivot Sum of = Sum of

26 Centre of

gravity

Point of an object through which its whole weight appears to act on for any orientation of the

object

27 Stability Ability of an object to return to its original position after it

has been tilted slightly Stable, unstable, neutral

28 Power Rate of work done or energy converted or transferred P = ΔEnergy † Time, Q = Pt

# Term Definition Related Formulas

29 Work done Product of the force acted on a body and the distance

travelled by the body in the direction of the force Work done = F d

30 Total work

done

Total work done = Work done by gravity (Gravitational

Potential energy) + Work done to increase speed (Kinetic

energy) + Work done over a distance to overcome friction

(Thermal energy) + [Other potential energy]

T.w.d. = mgh + ½ mv2 - ½ mu2 + fd

31 Efficiency Useful energy as a percentage of energy converted % = Energy output

x 100% Energy input

32 Pressure Normal force per unit area Pnormal = F/A, Pliquid = hverticalρg

33 Atmospheric

pressure

Pressure exerted on the Earth‟s surface due to the

molecular bombardment of energetic air molecules in the

atmosphere, being 1.013 x 105 Pa or 760 mm Hg

Density of mercury =

13.6 x 103 kg m-3

34 Heat Amount of thermal energy transferred from a hotter region to a colder region

35 Temperature Degree of hotness or coldness at a region T (K) = θ (°C) + 273

36 Brownian mo-

tion principle

Small particles suspended in a liquid or gas tend to move in random paths through the liquid or

gas even if it is calm

37 Gas laws

For a fixed mass of gas at constant temp, pressure is

inversely proportional to the volume of the gas. For a fixed

amount of gas at fixed pressure, volume is directly

proportional to the Kelvin temp. At constant volume, the

pressure is directly proportional to the Kelvin temp

P1V1T2 = P2V2T1

38 Heat capacity Amount of heat required to raise a body‟s temperature by

one degrees Celsius or Kelvin Q = Cθ

39 Specific heat

capacity

Amount of heat required to raise one kilogram of a body‟s

temperature by one degrees Celsius or Kelvin Q = mcθ

40 Sensitivity Change in length of mercury per unit temperature change

and is β to the range of the thermometer

S α Bulb

S β Bore

41 Respon-

siveness

Rate at which thermometer responds to a unit change in

temperature

R β Liquid volume

R β Bulb wall

42 Centigrade

scale

Temperature scales from resistance, pressure and length of

mercury thread θ =

Xθ - X0 x 100°C

X100 - X0

42 Thermocouple

scale e.m.f. in terms of voltage α Δ θ

θ - A =

Xθ emf XA

B - A XB emf XA

43 Latent heat Heat required to change a substance from one state to

another without any change in temperature Q = mL

44 Internal

energy

Kinetic and potential energy of particles in a body due to the movement and arrangement of the

particles

45

Law of

conservation

of heat energy

When substances are placed in full contact of each other,

total heat lost by hot substances is equal to the total heat

gained by cold substances

Heat lost by A = Heat gained by

B

46 Evaporation Change of state from a liquid to gas that can occur at any

temperature between melting and boiling points

α Temperature

α Exposed surf.

α Air movement

β Humidity

β Pressure

β Boiling pt

47 Conduction Process by which heat is transmitted through a medium from one particle to another

48 Convection Transfer of thermal energy by means of heated particles by currents in a liquid or gas

49 Radiation Heat transfer by the continual emission of infrared waves

from body surfaces without the aid of a material medium

[to] Reflection α Shiny surf.

[from] Radiation β Shiny surf.

Image Functions Object location Comparisons Image location

DIR Telescope Infinity At f

DIR Camera, Eye Behind 2f Between f and 2f

SIR Photocopier At 2f At 2f

MIR Projector Between f and 2f Behind 2f

MUV Spotlight At f Infinity

MUV Magnifying glass, Specs Between f and 0 Between -f and -2f

TERMINOLOGY AND FORMULAE

1) Inertia [1]

2) Mass [1]

3) Weight [1]

4) Gravitational field

strength [1]

5) Laws of reflection [1]

6) Images on mirrors [2]

7) Refraction [1]

8) Laws of refraction and

refractive index [2]

9) Critical angle [1]

10) Total internal reflection

[1]

11) Principal axis [1]

12) Principal focus [1]

13) Focal length [1]

14) Magnification [1]

15) Acceleration [1]

16) Displacement [1]

17) Velocity [1]

18) First law of motion [1]

19) Second law of motion [1]

20) Net force [1]

21) Terminal velocity [1]

22) Principle of Conservation

of Energy [1]

23) Moment [1]

24) Principle of moments [1]

25) Centre of gravity [1]

26) Stability [1]

27) Power [1]

28) Work done [2]

29) Total work done [1]

30) Efficiency [2]

31) Pressure [2]

32) Atmospheric pressure

[2]

33) Heat [1]

34) Temperature [1]

35) Brownian motion principle

[1]

36) Gas laws [1]

37) Heat capacity [1]

38) Specific heat capacity [1]

39) Sensitivity [4]

40) Responsiveness [3]

41) Centigrade scale [1]

42) Thermocouple scale [1]

43) Latent heat [1]

44) Internal energy [1]

45) Law of conservation of heat energy [1]

46) Evaporation [7]

47) Conduction [1]

48) Convection [1]

49) Radiation [2]

OTHER FORMULAE

1) Energy changes in speed and height [3]

2) Pressure difference in relation to force and area in a hydraulic system [2]

GENERAL QUESTIONS

1) What precautions should be undertaken to measure period of a pendulum? [2]

2) Compare mass and weight with 5 comparisons [5]

3) Why should we measure an object at at least three different positions? [2]

4) What is the speed of light in vacuum? [1]

5) What is optical fibre? [1]

6) Why are optical fibres more advantageous than copper wires? [2]

7) Is the principal focus always at the same position? What is principal focus dependent on? [1]

8) What happens to the image when the bottom half or top half of the lens depicting the image is

covered by an opaque material? [1]

9) Draw the graphs of the for increasing acceleration, decreasing acceleration, increasing

deceleration and decreasing deceleration. [4]

10) Draw the free body diagrams of an object being thrust upwards, an object being released high

up, an object being thrust high up, an stationary object on the ground, an object being pushed

on the ground and a flying airplane. [5]

11) Copy this table and fill in the blanks. [3]

Equilibrium Centre of gravity before and after

released

Change in equilibrium after

releasing

Stable equilibrium

Unstable equilibrium

Neutral equilibrium

12) How can stability to increased? [2]

160

13) In what situation does stability become maximum? [1]

14) Copy this table and fill in the blanks. [3]

Pendulum bob Affects bob‟s maximum height? Reasons

Contact between bob and air

Contact between fulcrum and string

String tension

15) Why does a smoke particle move in a constant random erratic motion? [2]

16) Why doesn‟t an empty drink can crush although atmospheric pressure exerts on it? [2]

17) Convert degrees Celsius to Kelvin. [1]

18) Account for the relationship between volume and pressure when temperature is constant. [2]

19) Account for the relationship between temperature and volume when pressure is constant. [2]

20) Account for the relationship between temperature and pressure when volume is constant. [2]

21) Describe the procedure to calibrate a thermometer. [3]

22) Copy this table of comparison and fill in the blanks. [3]

23) How is a laboratory thermometer adapted? Explain each adaptation. [4]

24) How is a clinical thermometer adapted? Explain each adaptation. [2]

25) Why is there no change in temperature during melting, boiling, freezing, condensation? [4]

26) What affects the melting and boiling points of a pure substance? How do they affect the

melting and boiling points? [2]

27) How does a pressure cooker decrease cooking time? [2]

28) Why does conduction take place? [2]

29) Why is conduction of heat better in solids than in liquids and gases? [2]

30) Why is conduction of heat in metals better than in non-metals? [2]

31) How does the convection current work in liquids? [2]

32) Why can‟t convection occur in solids? [2]

33) Why do we feel a sea breeze at a beach in the day? [2]

34) How does radiation work? [2]

35) What affects the rate of radiation? [2]

36) Fill in the following on the image location, properties and usage of these properties of a

converging lens. [6]

Object location Image location Properties Usage

-END-

Mercury Alcohol Thermocouple

Glass

Dying

Reaction

Expansion

Range

Cost

Accuracy

Safety

ANSWERS TO GENERAL QUESTIONS

1) What precautions should be undertaken to measure period of a pendulum? [2]

Ensure that the string is taut so that the period for every oscillation is almost for each of the 20

oscillations before taking the average. [1] Ensure that the angle of swing is less than 10 degrees for

minimal air resistance from contact with the air to prevent inaccuracy. [1]

2) Compare mass and weight with 5 comparisons [5]

scalar vector [1]

electronic mass balance, beam

balance

spring balance [1]

constant varies with gravity from place to place [1]

measured in kg measured in N [1]

amount of matter in an object force of attraction exerted on an object due to gravity [1]

3) Why should we measure an object at at least three different positions? [2]

It is to minimise errors [1] due to the non-uniformity of an object as the dimensions of an object may

vary at different locations. [1]

4) What is the speed of light in vacuum? [1]

The speed of light is 3.0 x 108 ms-1 [1], which is equal to all other EM waves when they travel in

vaccum.

5) What is optical fibre? [1]

It is a tube made of flexible glass material which transports data for internet communications

through light pulses by total internal reflection. [1]

6) Why are optical fibres more advantageous than copper wires? [2]

Carries data at a faster rate than copper wires as it makes use of light than current hence less signal

loss [1], and much weigh less than copper, hence enabling easier transport. [1]

7) Is the principal focus of a converging lens always at the same position? What is principal focus

dependent on? [1]

No. The principal focus depends on the angle that the light ray is incident on the surface of the lens.

[1] However, even if the angle of incidence of the light ray is more than 0 degrees, the focal length

will still be the same.

8) What happens to the image when the bottom half or top half of the lens depicting the image is

covered by an opaque material? [1]

The intensity of the image will be decreased by half.

f = x

f = x

9) How is scale written in a ray diagram of a lens depicting an image? [2]

Principal axis scale (vertical line) ? cm : ? cm [1]

Object scale (horizontal line) ?cm : ?cm [1]

10) Draw the graphs of the for increasing acceleration, decreasing acceleration, increasing

deceleration and decreasing deceleration. [4]

v v v v

t t t t

11) Draw the free body diagrams of an object being (1) thrust upwards, (2) an object being

released high up, (3) an stationary object on the ground, (4) an object being pushed on the

ground and (5) a flying airplane. [5]

Object thrust

upwards

Object released

high up

Object on the

ground

Object pushed

on the ground

A flying airplane

T

aR W

aR

W

+F

W +Contact force

+F *f F

W *Friction

T

aR F

W

12) Copy this table and fill in the blanks. [3]

Equilibrium Centre of gravity before and when released Change in equilibrium after release

Stable equilibrium rises and falls -

Unstable equilibrium falls and falls further usually turns to the neutral e.

Neutral equilibrium remains the same -

13) How can stability to increased? [2]

Increase base area. [1] Lower the center of gravity. [1]

14) In what situation does stability become maximum? [1]

When the center of gravity and the fulcrum are directly above or below each other. [1] As the

distance between the center of gravity and fulcrum increases, stability decreases.

Stable Unstable

F F F

15) What has to be present in a vector diagram to ensure maximum marks? [1] (removed question)

Labelled arrows with the forces and angles annotated.

16) Copy this table and fill in the blanks. [3]

Pendulum bob Affects bob’s maximum height? Reasons

Contact between bob and air Yes Air resistance is present

Contact between fulcrum and string Yes Friction is present between

String tension No Perpendicular to movement of bob

17) Why does a smoke particle move in a constant random erratic motion? [2]

The smaller and lighter air particles bombard the smoke particle continuously at random periods of

time, causing the smoke particle to move from place to place irregularly.

18) Why doesn‟t an empty drink can crush although atmospheric pressure exerts on it? [2]

Air molecules in the can travel around the can and collide with the interior surfaces of the can,

exerting a force. Force per unit area increases, and volume per unit area increases, causing pressure

to increase and become equal to atmospheric pressure. Hence it does not crush.

19) Convert degrees Celsius to Kelvin. [1]

Kelvin temperature = Celsius temperature + 273

20) Account for the relationship between volume and pressure when temperature is constant. [2]

As volume decreases, pressure increases. [No mark]

This is because as volume decreases, the concentration of gas molecules is higher, resulting in the gas

molecules to collide more frequently with the walls of the container. [1] This increases the force

acting on the surface. As area remains the same, force per unit area increases as well, hence

increasing pressure. [1]

21) Account for the relationship between temperature and volume when pressure is constant. [2]

As temperature increases, volume increases. [No mark]

This is because as temperature increases, the kinetic energy of the gas molecules increases, resulting

in the gas molecules to collide with the walls more frequently. [1] This increases the force acting on

the surface. The gas will expand until its pressure balances atmospheric pressure (if the walls are

flexible and allows expansion.) [1]

22) Account for the relationship betwen temperature and pressure when volume is constant. [2]

As temperature increases, volume increases. [No mark]

This is because as temperature increases, the kinetic energy of the gas molecules increases, resulting

in the gas molecules to collide with the walls more frequently. [1] This increases the force acting on

the surface. As the area remians the same, force per unit area increases as well, hence increasing

pressure. [1]

23) Describe breifly the procedure to calibrate a thermometer. [3]

1.Put thermometer in melting ice and mark on the thermometer the lower fixed point of 0 °C.

2.Put thermometer in steam and mark on the thermometer the upper fixed point of 100 °C.

3.Divide the the interval between the fixed point into 100 equal parts, each 1 degree Celsius.

24) Copy this table of comparison of properties and fill in the blanks where needed. [3]

Mercury [1] Alcohol [1] Thermocouple [1]

Glass Does not stick to glass Sticks to glass occasionally

Dying No dying, has visible meniscus Needs to be dyed

Reaction Reactions quickly to changes Slightly unreactive Senses temp. changes

rapidly

Expansion Uniform Not uniform

Range Good upper limit with high

boiling point

Good lower limit with low

melting point

High range of -200 deg to

1500 deg

Cost Expensive Cheap Expensive

Accuracy Small junction, can

measure specific locations

Safety Poisonous Safe

25) How is a laboratory thermometer adapted? Explain each adaptation. [4]

It has a narrow diameter to increase sensitivity. [1]

It has a thinner bulb wall to increase responsiveness. [1]

It has a longer stem to increase range. [1]

It has an oval glass stem to act as an magnifying glass to easier reading. [1]

Sensitivity Responsiveness Range View smaller range thinner bulb wall smaller sensitivity Oval glass stem >>

Magnifying glass

larger bulb smaller liquid volume longer stem

smaller bore

26) How is a clinical thermometer adapted? Explain each adaptation. [2]

It has a short range to increase sensitivity and save costs on glass. [1]

It has a constrictor to prevent the liquid level to fall back immediately, allowing an accurate taking of

the reading. [1]

27) Why is there no change in temperature during melting, boiling, freezing, condensation? [4]

During melting and boiling, energy is absorbed to break the strong bonds between the molecules in

order to change its state from solid to liquid and liquid to gas respectively. [2] During freezing and

condensation, energy is released to form stronger bonds between the molecules in order to change

its state liquid to solid and gas to liquid respectively. [2]

28) What affects the melting and boiling points of a pure substance? How do they affect the

melting and boiling points? [2]

The presence of impurities and the increase of pressure increases boiling points and decreases

melting points. The presence of impurities cause the substance to melt/boil over a range of

temperatures.

29) How does a pressure cooker decrease cooking time? [2]

The pressure cooker is airtight except for a small hole, which weights are put on the hole so that

pressure is more than atmospheric pressure. [1] Due to higher pressure, the boiling point of water

increases, causing the food to be heated more. [1]

30) Why does conduction take place? [2]

The particles at where the object is heated gains kinetic energy and vibrates, [1] colliding with the

neighbouring particles and transferring energy to them, allowing them to gain kinetic energy as well

and transfer energy to more surrounding particles [1] until the whole object gains heat. Hence heat is

transferred throughout the object and conduction occurs.

31) Why is conduction of heat better in solids than in liquids and gases? [2]

The particles in the solid are closer together [1] and the particles collide with one another more

frequently, [1] hence transfer of energy is much faster.

32) Why is conduction of heat in metals better than in non-metals? [2]

There are free electrons present in metals [1] that can travel in spaces between particles to collide

with each other, [1] transferring energy to them.

33) How does the convection current work in liquids? [2]

When the liquid is heated, the bottom portion of the liquid increases in temperature, becomes less

dense and rises up to take the place to the cooler, denser, upper portion of the liquid. [1] This denser

portion sinks to the bottom to be heated up to become less dense, and this cycle forms a convectional

current. [1]

34) Why can‟t convection occur in solids? [2]

Convection requires the bulk movement of molecules. [1] Solids have particles closely packed to one

another, and hence this disallows solids from being able to flow and move in clusters, unlike liquids.

35) Why do we feel a sea breeze at a beach in the day? [2]

In the day, land absorbs heat faster than the sea as it has a higher specific heat capacity, causing

the air above it to be heated up faster too. [1] Hot air is less dense than cool air, it will rise to move

up from the land and heads the sea while the denser cool air will sink and rush towards the land,

forming a land breeze. [1]

36) How does radiation work? [2]

All hot objects are able to release infrared waves. [1] When these infrared waves are received by

another object, it is converted into heat energy to be absorbed by the object. [1]

37) What affects the rate of radiation? [2]

If the temperature decreases, the rate of radiation will decrease. [1]

The darker the object, the higher the rate of radiation, which also means a lower rate of absorbing

and emitting of heat. [1]

The higher the total surface area of the object, the higher the rate of radiation. [1]

38) Fill in the following on the image location, properties and usage of these properties of a

converging lens. [6]

Object location Image location Properties Usage

Infinite At f DIR Telescope [1]

More than 2f Less than 2f and

more than f

DIR Camera, Eye [1]

At 2f At 2f SIR Photocopier for same

size printing

[1]

Less than 2f and

more than f

More than 2f MIR Projector [1]

At f Infinite MUV Spotlight [1]

Less than f More than -2f

less than -f

MUV Magnifying glass [1]

-END-