Physical SciencesPhysics Grade 12
Textbook and Workbook
Lida Smith • Hendry du Plessis Isolde Fasondini • Marga Koelman
Carlien Fanoy • Santie du PlessisJudy McDougall • Corlia Wepener
Annemie SmitSample
Doc ScientiaP.O. Box 7011
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www.docscientia.co.za
For any queries and feedback: [email protected]
Jacques Fanoy or Stephan FanoyOffice: 011 022 0750
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ISBN: 978-1-920537-20-3
First edition December 2009Second edition December 2010
Third edition December 2011Fourth edition December 2012
Fifth edition December 2013
Graphic design: Helene Jonck
All rights reserved. No part of this publication may be reproduced in any form or by any means –
mechanical or electronic, including recordings or tape recordings and photocopying – without the prior permission of the publisher.
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Dear Grade 12 learner
To take Physical Sciences is challenging and hard work. The rewards are excitement, new discoveries and creative thoughts.
The knowledge you have gained each year has been building blocks in a greater picture. If there are any blocks missing, the picture does not make sense. Therefore, we must be aware of the fact that all the blocks have to be taken with us from one year to the following. It is a good idea to always have your Grade 10 and 11 Workbooks close by for reference.
You need the following skills:• Common sense There is a lot of logic in science, because it deals with everyday happenings, like cars that crash, rugby balls being kicked and so much more.• Calculator skills Be sure you know how to use your calculator.• Know your formula page. Know what each symbol stands for and in which unit each amount is measured.• Reading skills A lot of information will come to you in the form of words. Learn to read with insight and use a highlighter to emphasize the facts you will need, or draw circles around it. • Draw pictures. There is nothing that helps you think as logically as pictures.• Practise, practise, practise. It still is the best method of learning something. It means that you always have to do your homework on your own. Work through old exam papers and our Exercise book; it provides valuable experience.
The short explanations, examples, summaries, mind maps and exercises will help you gain the necessary knowledge to master Physical Sciences.
Use the video referencs to understand some of the terms better. However, remember to use Google as you search engine.
We hope that this will be a successful year, full of excitement and fun.
Doc Scientia
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INDEXUnit Page
SKILLSSKILLS FOR PRACTICAL INVESTIGATIONS1.1 Development of sciences 111.2 Scientific research 121.2.1 Types of research 141.2.2 Variables 141.2.3 Relationship between variables 151.2.4 Table 161.2.5 Other information to analyse the data 161.2.6 Conclusion and evaluation 17Exercise A 201.3 Lab equipment 241.3.1 Thermometers 241.3.2 Scales 251.3.3 Metre stick 261.3.4 Graduated cylinder 261.3.5 Pipette 261.3.6 Burette 27Activity 28Exercise B 30
KNOWLEDE AREA MECHANICS 35Unit 1 MOMENTUM AND IMPULSE 35
1.1 Momentum 351.2 Change in momentum 36Exercise 1 391.3 Newton’s second law in terms of
momentum 431.4 Impulse 46Exercise 2 511.5 The law of conservation of momentum 57Experiment 1 611.6 Elastic collisions 63Experiment 2 (demonstration) 64Exercise 3 66Summary of Unit 1 74
Unit 2 PROJECTILE MOTION 772.1 What is a projectile? 772.2 Gravitational acceleration 77Experiment 3 792.3 Terminal velocity 812.4 Equations of motion 81
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KNOWLEDE AREA WAVES, SOUND AND LIGHT 1711 Introduction 1712 The Doppler effect 1712.1 Sound and ultrasound 1712.1.1 Stationary sound source and listener 1722.1.2 Moving sound source and stationary
listener 172Experiment 5 (demonstration) 1732.1.3 Calculations 1752.1.4 Application 1772.1.4.1 Nature 1782.1.4.2 Other applications 1782.1.4.3 Medical field 1792.2 Light 180Exercise 8 182Summary 186Question paper 189Mind maps 195
KNOWLEDE AREA ELECTRICITY AND MAGNETISM 197Unit 1 ELECTRIC CIRCUITS 197
1.1 Introduction 1971.1.1 Potential difference 1971.1.2 Current 1981.1.3 Resistance 198
2.5 Problem solving 82Exercise 4 97Summary of Unit 2 109
Unit 3 WORK, ENERGY AND POWER 1123.1 Work and energy 1123.1.1 Work (W) 1123.1.2 Resistance forces (friction) 116Exercise 5 1173.1.3 Potential energy (EP) 1233.1.4 Kinetic energy (EK) 1243.1.5 Mechanical energy 1253.1.6 The work-energy principle 1263.1.7 Forces 131Exercise 6 1363.2 Power or rate of work (P) 146Experiment 4 147Exercise 7 149Summary of Unit 3 153Question paper 157Mind maps 169
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1.1.4 Series and parallel connections 1991.2 Internal resistance 200Experiment 6 203Experiment 7 208Exercise 9 213Summary of Unit 1 220
Unit 2 ELECTRODYNAMICS 2242.1 Electromagnetic induction and electric
generators 2252.1.1 Direct current generators 2272.1.2 Alternating current generator
(alternator) 2292.1.3 Comparison of DC and AC generators 230Project 230Exercise 10 2322.2 The motor effect and electric motors 2362.2.1 Direct current motors (DC motors) 2382.2.2 Alternating current motors (AC
motors)240
2.2.3 Comparison of DC and AC motors 241Project 241Exercise 11 2422.3 Alternating current 2442.3.1 Change in potential difference and
current for AC 2452.3.2 Root mean square current and potential
difference 246Exercise 12 248Summary of Unit 2 255Question paper 261Mind maps 272
KNOWLEDE AREA MATTER AND MATERIALS 275Unit 1 PHOTOELECTRIC EFFECT 275
1.1 Transmission and scattering of light 2751.2 What is the photoelectric effect? 276Experiment 8 (demonstration) 2771.3 Work function and threshold frequency 2801.4 Intensity and frequency of light 2841.5 The quantum theory 286Exercise 13 287Summary of Unit 1 294
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Unit 2 EMISSION AND ABSORPTION SPECTRA 2972.1 Emission spectra 2972.1.1 Continuous emission spectrum 2972.1.2 Line emission spectrum 2972.2 Absorption spectra 2982.2.1 Infrared spectra 2992.3 Differences between the different
spectra 299Exercise 14 300Summary of Unit 2 303Question paper 305Mind maps 314Information sheets 317Work cited 320
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KNOWLEDGE AREA:MATTER AND MATERIALS
Doc Scientia PHYSICS textbook and workbook - Grade 12
SpectraA spectrum forms if a light bundle is broken up into the composite light of different frequencies b.m.o. refraction. The process is known as dispersion.A light bundle can be diffracted by various devices, e.g. a triangular prism, diffraction grating or a spectroscope.There are two main spectrum groups:• Emission spectra• Absorption spectra
2.1 Emission spectra2.1.1 Continuous emission spectrumWhen white light passes through a triangular prism, it shows a continuous spectrum of colours (ROYGBIV – red, orange, yellow, green, blue, indigo and violet). The spectrum’s colours follow each other continuously without any gaps occuring between the colours. It is similar to the appearance of a rainbow.
2.1.2 Line emission spectraWhen an electric current is passed through a gas, the gas emits light (glow state). The spectrum which is produced by the glowing gas consists of individual bright coloured lines. This is a line emission spectrum.
Line emission spectra
Differences between the spectra
Continuous emissionspectrum
Absorption spectra
UNIT 2 EMISSION AND ABSORPTION SPECTRA
Emission and absorption spectra
Emission spectra
EM spectrum contains the visible light spectrum.
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matter and materials
Doc Scientia PHYSICS textbook and workbook - Grade 12
This happens because the electrons of the gas are excited to higher energy levels. The energy of the photons match the difference in energy between the energy levels into which the electrons fall. Elements have unique energy levels and therefore also unique line emission spectra. Do you still remember the flame tests done in Grade 10 on certain elements? Each element had its own distinctive colour by which it could be identified. When the electrons fall back again to lower energy levels, the energy is irradiated in the form of light, in other words, photons.
The line emission spectra of hydrogen are represented above.
2.2 Absorption spectra
Absorption spectra are formed when light is sent through a cold diluted gas. The atoms of the gas absorb certain frequencies of light. The absorbed frequencies appear as black lines in the continuous spectrum of white light. When an electron absorbs a photon, the electron moves to a higher energy level.
When the electron then falls back again, the emitted photon is not necessarily emitted in the same direction as the absorbed photon. This scattered light causes certain gases to have a specific colour. In order to see the black lines, which cannot be seen with the naked eye, the light has to be dispersed by diffraction grating.
Lyman series
Lyman seriesultraviolet
Balmer series
Balmer seriespartly visible
Paschen series Paschen seriesinfrared
n = 1
n = 2
n = 3
n = 4
122 nm
103 nm
656 nm 486 nm434 nm
410 nm
1 875 nm
1 282 nm
1 094 nm
97 nm
95 nm
94 nmlevel
1
2
3
spectrum
frequency (PHz)0 0,5 1,0 1,5 2,0 2,5 3,0 3,5
hydrogen absorption spectrum
hydrogen emission spectrum
400 nm 700 nm
H alpha line 656 nmtransition n = 3 to n = 2Sample
matter and materials
Doc Scientia PHYSICS textbook and workbook - Grade 12 299
Each element absorbs unique frequencies and the spectrum is characteristic of a specific element, and can be used to identify the element.
Quick facts:The sun has a continuous spectrum, with black absorption lines with which the element in the outer layer of the sun can be identified.
2.2.1 Infrared spectra
Atoms in molecules vibrate. These vibrations depend on:• the strength of the bonds. • the mass of the atom.• the shape of the molecule.
Just as only certain energies are absorbed and emitted by electrons, only photons with certain energies can cause vibrations in bonds between atoms in a molecule.These energiesoccurs in the infrared part of the spectrum. The shape of the molecules also determines the vibrations. Only polar bonds of which the dipole moment changes when the molecule vibrates, will lead to infrared absorption. The absorption causes the vibration to be more energetic and it increases the average bond length.
Visible light from the sun is absorbed by the earth and the temperature of earth increases. The earth radiates the energy in the form of infrared radiation. CO2 (carbon dioxide) and H2O (water vapour) can absorb infrared radiation from the earth at different frequencies, which explains why these gases are natural greenhouse gases that trap the heat of the earth.
Diatomic gases like O2 (oxygen) and N2 (nitrogen) have no change in their dipole moment when they vibrate, and absorb no infrared radiation.
2.3 Differences between the different spectra
Line emission Absorption Infrared
• Spectrum emitted by a glowing gas.
• Brightly coloured lines
• White light shines through a cold diluted gas.
• Black lines appear in the continuous spectrum.
• Cause bonds between atoms to vibrate.
• Vibration depends on the type of bond and the mass of the atom.
Sample
matter and materials
300 Doc Scientia PHYSICS textbook and workbook - Grade 12
Line emission Absorption Infrared
How• e- excited to higher energy
levels.• e- falls down to lower energy
levels and radiates photons.
How• Photons with a specific
frequency are absorbed.• Absorbed energy with
frequency f is shown as a black line.
How• Only specific photons are
able to cause vibration.• Only molecules with polar
bonds with a changing dipole moment can vibrate.
http://www.youtube.com/watch?v=jaOzC0leAdkhttp://www.youtube.com/watch?v=IfJS9nji_Lshttp://www.youtube.com/watch?v=snNwE6txxP0
Exercise 14 Date:1 CO2 and H2O are called greenhouse gases.1.1 What is the greenhouse effect?
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1.2 Which characteristics in the bonds of CO2 and H2O play an important part in the absorption of infrared radiation from earth?
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1.3 Explain why CO2 and H2O are called greenhouse gases, but O2 and N2 are not.
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2 In the sun, the inner sphere is a lot hotter than the outer sphere.
outer sphere
inner sphere
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matter and materials
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2.1 Why can we observe an absorption spectrum of the sun?
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2.2 What information can we deduce from this spectrum?
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3. The earth absorbs higher frequency visible light and radiates lower frequency infrared rays. Which of these radiations has the longest wavelength? Motivate your answer.
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4. Explain the difference between a line emission spectrum and a line absorption spectrum.
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5. Discuss the similarity between a line emission spectrum and a line absorption spectrum.
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6. What is a line emission spectrum and a line absorption spectrum respectively used for?
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matter and materials
302 Doc Scientia PHYSICS textbook and workbook - Grade 12
7. Briefly explain what the greenhouse effect is and say how carbon dioxide and water vapour contribute to it.
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8. Due to global warming the tundra (which means treeless plane) in Siberia is melting. It releases massive amounts of methane gas that was previously trapped in the frozen ground. Methane absorbs even more infrared radiation than carbon dioxide and water vapour. Why is the increased concentration of methane gas a problem?
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9. For millions of years, carbon dioxide and water vapour have been present in the atmosphere. The greenhouse effect is one of the reasons why life on earth can continue. Explain why this is so.
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Notes: Sample
matter and materials
Doc Scientia PHYSICS textbook and workbook - Grade 12 303
Summary
• Continuousemissionspectrum: When white light shines through a triangular prism, it breaks up into a continuous emission spectrum of colour.
• Lineemissionspectrum: When a gas is electrified it glows and emits light. The resulting spectrum is known as a line emission spectrum, since it consists of a series of brightly coloured lines. Elements have unique energy levels and therefore have unique line emission spectrums.
• Absorptionspectrum: When light shines through a cold diluted gas, atoms of the gas absorb a specific energy with a specific frequency, an absorption spectrum is formed. The absorbed energy with a specific energy shows up as black lines in the spectrum.
• Infraredspectrum: In molecules, atoms vibrate. Only specific energies may be absorbed and emitted by the electrons. Therefore only specific photons are able to cause vibrations in bonds.
These energies are found in the infrared part of the spectrum.
Line emission Absorption Infrared
• Spectrum emitted by a glowing gas.
• Brightly coloured lines
• White light shines through a cold diluted gas.
• Black lines appear in the continuous spectrum.
• Cause bonds between atoms to vibrate.
• Vibration depends on the type of bond and the mass of the atom.
How• e- excited to higher
energy levels.• e- falls down to lower
energy levels and radiate photons.
How• Photons with a
specific frequency are absorbed.
• Absorbed energy with frequency f is shown as a black line.
How• Only specific photons are
able to cause vibration.• Only molecules with polar
bonds with a changing dipole moment can vibrate.
Absorption
Infrared spectrumContinuous emission spectrum Line emission spectrum
Spectra
Emission
Sample
Transmission and dispersion of light
Work function and threshold frequency
Work function (W0) of a metal
Threshold frequency (f0)
E < W0E = W0E > W0
• Higher frequency of light =
• Higher intensity of light =
Definition and formulae
PHOTOELECTRIC EFFECT
Sample
Continuous emission spectrum
Line emission Absorption Infrared
How How How
Line emission spectrum Absorption Infrared spectra
SPECTRA
AbsorptionEmission
Sample
