Physical Sciences Physics Grade 12 Textbook and · PDF filePhysical Sciences. Physics Grade 12 Textbook and . ... Practical activity ... Experiment 4: 146 Exercise 7: 148

Physical SciencesPhysics Grade 12

Textbook and Workbook

Hendry du Plessis • Santie du PlessisCarlien Fanoy • Isolde Fasondini

Marga Koelman • Judy McDougallAnnemie Smit • Lida Smith

Corlia Wepener

Doc ScientiaPosbus 7011

Ansfrere 1711

www.docscientia.co.za

For any queries and feedback: [email protected]

Jacques Fanoy or Stephan FanoyOffice: 011 472 8728

Fax: 086 546 1423

ISBN: 978-1-920537-20-3

First edition December 2009Second edition December 2010

Revised edition December 2011; 2012Third edition December 2013

Revised edition December 2014; 2015; 2016

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.

Dear Grade 12 learner

To study 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 own homework. 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 QR codes to understand some of the terms better.

We trust it will be a successful year filled with excitement and achievements.

Doc Scientia

Enrichment

How to use this workbook:

• The book is divided into knowledge areas. • Each knowledge area is divided into units.• After each unit there is an exercise and a summary.• After each knowledge area there is a question paper and mind

maps.• The format of a question paper is similar to end-of-year exams.The following can be found throughout the book:

ActivityAny activity that is done with pen and paper.

Practical activityA simple investigation or experiment to understand the theory better.

ExperimentThe method of the experiment is given step by step, and you should follow it to get results. Experiments confirm the theory.ORIt is expected of you to plan and carry out the experiment to obtain results.

Examples

Question paperProject

Use your smartphone to activate the QR codes.

Definitions and formulae

Interesting facts

Quick facts

RememberSummary

Notes

Case study

INDEXUnit Page

SKILLS

SKILLS FOR PRACTICAL INVESTIGATIONS

1.1 Development of sciences 11

1.2 Scientific research 12

1.2.1 Types of research 14

1.2.2 Variables 14

1.2.3 Relationship between variables 15

1.2.4 Table 16

1.2.5 Other information to analyse the data 16

1.2.6 Conclusion and evaluation 17

Exercise A 20

1.3 Lab equipment 24

1.3.1 Thermometers 24

1.3.2 Scales 25

1.3.3 Meterstick 26

1.3.4 Graduated cylinder 26

1.3.5 Pipette 26

1.3.6 Burette 27

Activity 28

Exercise B 30

KNOWLEDE AREA MECHANICS 33

Unit 1 MOMENTUM AND IMPULSE 33

1.1 Momentum 33

1.2 Change in momentum 34

Exercise 1 37

1.3 Newton’s second law in terms of momentum 41

1.4 Impulse 44

Exercise 2 49

1.5 The law of conservation of momentum 55

Experiment 1 59

1.6 Elastic collisions 61

Experiment 2 (demonstration) 62

Exercise 3 64

Summary of Unit 1 71

Mind maps of Unit 1 73

Unit 2 PROJECTILE MOTION 75

2.1 What is a projectile? 75

2.2 Gravitational acceleration 75

Experiment 3 77

2.3 Terminal velocity 79

2.4 Equations of motion 79

2.5 Problem solving 80

Exercise 4 95



Unit 3 WORK, ENERGY AND POWER 111

3.1 Work and energy 111

3.1.1 Work (W) 111

3.1.2 Resistance forces (friction) 115

Exercise 5 116

3.1.3 Potential energy (EP) 122

3.1.4 Kinetic energy (EK) 123

3.1.5 Mechanical energy 124

3.1.6 The work-energy principle 125

3.1.7 Forces 130

Exercise 6 135

3.2 Power or rate of work (P) 145

Experiment 4 146

Exercise 7 148



Question paper 157

KNOWLEDE AREA WAVES, SOUND AND LIGHT 169

1 Introduction 169

2 The Doppler effect 169

2.1 Sound and ultrasound 169

2.1.1 Stationary sound source and listener 170

2.1.2 Moving sound source and stationary listener 170


2.1.3 Calculations 173

2.1.4 Application 175

2.1.4.1 Nature 176

2.1.4.2 Other applications 177

2.1.4.3 Medical field 177

2.2 Light 178

Exercise 8 179

Summary 183

Mind maps 185

Question paper 187

KNOWLEDE AREA ELECTRICITY AND MAGNETISM 193

Unit 1 ELECTRIC CIRCUITS 193

1.1 Introduction 193

1.1.1 Potential difference 193

1.1.2 Current 194

1.1.3 Resistance 194

1.1.4 Series and parallel connections 195

1.2 Internal resistance 196

Experiment 6 199

Experiment 7 204

Exercise 9 209



Unit 2 ELECTRODYNAMICS 221

2.1 Electromagnetic induction and electric generators222

2.1.1 Direct current generator 224

2.1.2 Alternating current generator (alternator) 226

2.1.3 Comparison of DC and AC generators 227

Project 227

Exercise 10 229

2.2 The motor effect and electric motors 233

2.2.1 Direct current motors (DC motors) 235

2.2.2 Alternating current motors (AC motors) 237

2.2.3 Comparison of DC and AC motors 238

Project 238

Exercise 11 239

2.3 Alternating current 241

2.3.1 Change in potential difference and current for AC 242

2.3.2 Root mean square current and potential difference 243

Exercise 12 245



Question paper 261

KNOWLEDE AREA MATTER AND MATERIALS 271

Unit 1 PHOTOELECTRIC EFFECT 271

1.1 Transmission and scattering of light 271

1.2 What is the photoelectric effect? 272


1.3 Work function and threshold frequency 276

1.4 Intensity and frequency of light 280

1.5 The quantum theory 282

Exercise 13 283



Unit 2 EMISSION AND ABSORPTION SPECTRA 293

2.1 Emission spectra 293

2.1.1 Continuous emission spectrum 293

2.1.2 Line emission spectrum 293

2.2 Absorption spectra 294

2.2.1 Infrared spectra 295

2.3 Differences between the different spectra 295

Exercise 14 296



Question paper 301

Information sheets 309

Work cited 311

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. This 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 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.

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 = 2


Doc Scientia PHYSICS textbook and workbook - Grade 12 295

Each element absorbs unique frequencies and the spectrum is characteristic of a specific element, and can be used to identify the element.

Quick factsThe 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 energies occur 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.


296 Doc Scientia PHYSICS textbook and workbook - Grade 12


How• e- excited to higher energy

levels.• e- fall 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.

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



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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298 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



Summary

• Continuous emission spectrum: When white light shines through a triangular prism, it breaks up into a continuous emission spectrum of colour.

• Line emission spectrum: 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 spectra.

• Absorption spectrum: When light shines through a cold diluted gas and 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.

• Infrared spectrum: 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.


• 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- fall 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

Continuous emission spectrum


How How How

Line emission spectrum Absorption Infrared spectra

SPECTRA

AbsorptionEmission

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Physical Sciences Physics Grade 12 Textbook and · PDF filePhysical Sciences. Physics Grade 12 Textbook and . ... Practical activity ... Experiment 4: 146 Exercise 7: 148