6DPSOHMarina Schmidt • Lida Smithdocscientia.co.za/images/stories/pdf/Gr11_Physics_WB_2016.pdf · 1.6.4 Static friction ( f S) 32 1.6.5 Kinetic friction (f K ... Experiment 4 46

Physical SciencesPhysics Grade 11

Textbook and Workbook

Ronel Bernardo • Hendry du PlessisSantie du Plessis • Carlien FanoyElize Jones • Patricia Lees-Rolfe

Judy McDougall • Karen ReyneckeMarina Schmidt • Lida SmithSample

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: 978-1-920537-16-6

First edition December 2009Revised edition December 2010; 2011

Second edition December 2012Revised edition December 2013; 2014; 2015

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 11 learner

A year full of challenges lies ahead of you. You will be taught to ask questions and obtain solutions in creative ways. The framework for your Grade 12 year will finally be laid down. Keep your Grade 10 books at hand to refresh your memory if needed.For Physical Sciences you need the following skills:• Common sense There is a lot of logic in science because it deals with everyday events like cars that crash, rugby balls being kicked and many more.• Calculator skills Be sure to know how your calculator works. • Know you formula sheet. Know what each symbol represents and in which unit each quantity is measured.• Reading skills You will receive a lot of information in written form. Learn to read with insight and to highlight the facts that you need with a highlighter, or by drawing a circle around them. • Draw pictures. There is nothing like a picture to help you think logically. • Practise, practise, practise. It is still the best way to learn anything. This means that you should always do your homework yourself. Work through old exam papers; it is valuable experience.

In the workbook there are explanations, examples, summaries, mind-maps and exercises which will help you to overcome any obstacle in Physical Sciences. Also visit our website for more tips and the latest information.

We hope that this year will lay a solid foundation. May you find this year an exciting one.

Doc Scientia

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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, summary and mind maps.• After each knowledge area there is a question paper.• 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

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INDEXUnit Page

KNOWLEDGE AREA MECHANICS 11

Unit 1 VECTORS IN TWO DIMENSIONS 11

1.1 Scalars and vectors 12

1.2 Graphical representation of vectors 12

1.3 Division of a vector into components 12

Exercise 1 16

1.4 What is a force? 20

1.4.1 Non-contact forces 21

1.4.2 Contact forces 21

1.5 Forces and free force diagrams 22

Exercise 2 26

1.6 Friction force 28

1.6.1 Which factors influence the magnitude (size) of the frictional force? 29

1.6.2 Coefficient of friction 31

1.6.3 How to reduce friction 31

1.6.4 Static friction ( fS) 32

1.6.5 Kinetic friction (fK) 32

1.6.6 Application 36

Experiment 1 36

Experiment 2 38

Experiment 3 39

Exercise 3 40

1.7 Forces in equilibrium 43

1.8 Resultant or net force 44

1.9 Determining the resultant vector 44

1.9.1 The head to tail and tail to tail method 44

Experiment 4 46

1.9.2 Calculation 48

Exercise 4 51

Summary of Unit 1 56

Mind maps of Unit 1 59

Unit 2 NEWTON’S LAWS OF MOTION 61

2.1 Newton’s first law of motion 61

2.1.1 Inertia 62

2.1.2 Safety belts 63

Practical activity 1 63

Exercise 5 65

2.2 Newton’s second law of motion 67

Experiment 5 78

Experiment 6 82

Exercise 6 84

2.3 Newton’s third law of motion 91

Experiment 7 92

Exercise 7 94



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Unit 3 NEWTON’S LAW OF UNIVERSAL GRAVITATION 101

3.1 Law of universal gravitation 101

3.2 Mass and weight 104

3.3 Weightlessness 104

3.4 Relationship between g and G 105

Experiment 8 106

Exercise 8 108



Question paper 115

KNOWLEDGE AREA WAVES, SOUND AND LIGHT 129

Unit 1 GEOMETRIC OPTICS 129

1.1 Reflection 129

Exercise 9 130

1.2 Speed of light 131

1.3 Refraction 133

Experiment 9 133

1.3.1 Refractive index 137

1.3.2 Normal, angle of incidence and angle of refraction 138

Experiment 10 139

Exercise 10 141

1.4 Snell’s law 147

Experiment 11 150

Exercise 11 151

1.5 Critical angle 155

Experiment 12 155

1.6 Total internal reflection 157

Exercise 12 160



Unit 2 2D AND 3D WAVEFRONTS 167

2.1 Interference 168

2.2 Refraction 169

2.3 Diffraction of waves 169

2.3.1 Huygens’ principle 169

2.3.2 Diffraction of water waves 170

Experiment 13 (demonstration) 171

Exercise 13 173

2.3.3 Diffraction of light waves 176

Experiment 14 176

Experiment 15 178

Exercise 14 182



Question paper 189

KNOWLEDGE AREA ELECTRICITY AND MAGNETISM 201

Unit 1 ELECTROSTATICS 201

1.1 Forces between charges 202

1.1.1 Magnitude of charges 203

Sample

1.1.2 Distance between charges 204

1.1.3 Graphs 205

1.1.4 Coulomb’s law 205

Exercise 15 206

1.1.5 Net force 214

Exercise 16 216

1.2 Electric fields 222

1.2.1 Electric field lines 222

1.2.2 The electric field strength (E) 223

Exercise 17 225



Unit 2 ELECTROMAGNETISM 235

2.1 Magnetic effect of an electric current 235

Practical demonstration 1 236

2.1.1 Magnetic fields 238

2.1.2 Overhead cables: the impact on people and the environment 240

2.2 Electromagnetic induction 241


2.2.1 Direction of induced current 243

2.2.2 Magnetic field strength 244

2.2.3 Magnetic flux 244

2.2.4 Faraday’s law 247

Exercise 18 250



Unit 3 ELECTRIC CIRCUITS 259

3.1 Current 260

3.2 Potential difference 260

3.3 Resistance 261

Experiment 16 263

Experiment 17 265

Exercise 19 270

3.4 Energy transformation in a circuit 271

3.5 Power 271


Exercise 20 277

3.6 Cost calculations 280

3.7 Saving electricity 282

Exercise 21 283



Question paper 290

Information sheets 303

Work cited 305

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Doc Scientia PHYSICS textbook and workbook - Grade 11 167

KNOWLEDGE AREA: WAVES, SOUND AND LIGHT

UNIT 2 2D AND 3D WAVEFRONTS

Interference

Diffraction of water waves

Diffraction of light waves

Huygens’ principle2D and 3D wavefronts Refraction

Before we continue looking at the behaviour of waves, we need to revise the basic properties of waves. Basic knowledge of waves:• A pulse/vibration is a single disturbance in a medium.• Amplitude: maximum displacement from a position of rest.• Wavelength (λ) is the distance between two consecutive points in phase.• Frequency (f) is the number of complete waves that pass a given point per second. • Period (T) is the time taken for one complete wave to pass a point.• Two points are in phase if they both simultaneously conduct the same motion and are equal in

distance on the side of the position of rest.• A transverse wave: disturbance of the medium is perpendicular to the direction of movement of the

wave, e.g. water waves.• Longitudinal wave: disturbance of the medium is parallel to the movement of the wave, e.g. sound

waves. • A standing wave: the incident and reflected waves are in phase.

- Points where there is no disturbance are known as nodes.- Points where there is a maximum disturbance are known as antinodes.

Water waves will be used to study waves, since they are large and easily seen. Many of the properties of water waves can be applied to both sound and light waves. A ripple tank is the best apparatus to show the behaviour of water waves.When a single disturbance (pulse) is made in a ripple tank, a whole row of water particles move at the same time, which causes a pulse that moves away from the source. A number of regular repetitive disturbances will create a number of pulses with the same pulse length that will move away from the source. This is a wave. The projection of light through the ripple tank gives a pattern like that in the picture below: The light stripes are the crests. The dark bands are the troughs of the wave.

Diffraction of waves

Properties of waves

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waves, sound and light

168 Doc Scientia PHYSICS textbook and workbook - Grade 11

Properties of waves

2.1 InterferenceWhen a number of coherent sources close together produce waves of the same frequency, their waves will cross over each other and influence each other (interference).

Interference occurs due to superposition of waves. When two crests or two troughs meet, constructive interference occurs. When a crest and a trough meet, destructive interference occurs.

Interference is a phenomenon in which two waves superimpose to form a resultant wave of greater or lower amplitude.

Quick factsCoherent sources are sources that are in phase with each other.

There are two types of interference:

Constructive Destructive

• Two pulses that are in phase approach each other from opposite directions.

• Pulses meet: amplitude is the vector sum of the amplitudes of the two individual pulses.

• After interference, the pulses continue in their original directions.

• A crest and a trough (out of phase) approach each other from opposite directions.

• Pulses meet: amplitude is the vector sum of the amplitudes of the two individual pulses.

• If both pulses have the same amplitude, they will cancel each other out at the point of meeting.

After interfering, the two pulses will continue with their original speed and amplitude.

a + b

ba -ba

a + (-b) Sample



2.2 RefractionWhen a wave moves from one optical medium to another, refraction will take place.This can be shown in the ripple tank by placing an object at an angle in the water or by changing the depth of the water.

2.3 Diffraction of waves 2.3.1 Huygens’ principle

Huygens’ principle explains the manner in which waves bend when it moves around an obstruction.

His principle reads as follows:

All points on a wavefront act like a point source. Each one of these point sources (secondary sources) produces small circular waves moving forwards with the same speed as the wave. The new wavefront is obtained by drawing a tangent to all the new little wavefronts.

Interesting factsChristiaan Huygens was a Dutch mathematician and scientist.In 1678 he proposed a way of explaining the behaviour of waves.

The new wavefront is obtained by drawing a tangent to all the new little waves.

secondary wavefront

secondary source

original wavefront

source

new wavefront

original wavefront

each of these points is a source (secondary source) of a circular

little wave

constructive interference (crest with crest)

new (secondary) wavefront

destructive interference (crest with trough)

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These circular waves undergo interference with each other. Where they interfere constructively, a new wavefront is formed.

• The wavefront consists of multiple overlapping circular crests.• Each point on the original wavefront causes a small circular wave.• Where two crests or two troughs overlap, constructive interference takes place.• Where a crest and a trough overlap, destructive interference takes place.• The “sum” of all the little waves is the new wavefront. At very far distances where the wave originated,

the wavefronts appear almost as a line.

2.3.2 Diffraction of water wavesHuygens’ principle can be explained very easily with a point source, like a stone falling into water.The stone causes a circular wave, which moves away from the point of impact.

A wavefront is an imaginary line joining all the points in a wave that are in phase.

wavefront

On this wavefront there are millions of points.

Each point on the wavefront produces small circular waves, which move forward.

Only a few circular waves are shown.

Crests overlap: constructive interference occurs.

If a new tangent is drawn to each circle, a new wavefront is obtained.

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Diffraction explained according to Huygens’ principle

When an obstruction is placed in the path of a wave, the waves bend around the obstruction.

Waves will also bend around the sides of an opening in an obstruction.

This phenomenon is known as diffraction.

Diffraction: The ability of a wave to spread out in wavefronts as they pass through a small opening or around a sharp edge.

Experiment 13 (demonstration) Date:Aim: To investigate the diffraction of waves.

Apparatus: • Ripple tank • Two barriers • Ruler to produce waves.

Method: 1. Set up the ripple tank.2. Place barriers of different sizes in the path of the waves.3. Generate a wave with the ruler.4. Observe what happens when a wave hits a barrier.5. Make a small opening between two barriers.6. Observe what happens when the wave goes through the opening. 7. Change the size of the gap and observe how this changes the diffraction.

destruction

wavefronts

crest

trough

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Observations:1. What happens when the wave hits a barrier?

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2. Sketch what happens when the wave moves through a narrow opening.

3. Sketch what happens when the wave moves through a wider opening.

Conclusions:

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• When a wave travels in a straight line, it propagates small circular waves (secondary sources). When the wave hits an obstruction, the secondary sources moving past the obstruction (through the gap) will interfere with the neighbouring secondary sources. All points on the new wavefront now become the source for a new set of wavefronts. As long as the wave carries on, the process is repeated.Sa

mple



• A smaller opening produces greater diffraction. The maximum degree of diffraction occurs when circular wavefronts occur on the opposite side of an opening. This occurs when the width of the opening is equal to the wavelength of the wave, therefore w = λ.

• Complete diffraction occurs. • Longer wavelengths undergo greater diffraction. When the waves move

through the opening, the wavelength and frequency are not affected.The degree of diffraction depends on:

- the wavelength (λ). - the width of the opening (w). ○ The degree of diffraction is large when the opening is small. (Diffraction is inversely proportional to the width of the opening.) ○ The degree of diffraction is large when the wavelength is long. (Diffraction is directly proportional to the wavelength.) λ

○ The degree of diffraction ∝ w

Exercise 13 Date:1 A ripple tank is set up with water. Two wooden barriers are placed so that the opening between them is 12 cm. Waves with a wavelength of 1 cm are produced by a vibrator.

opening

wavefront

constructive interference: crest with crest from neighbouring source

destructive interference: crest with trough from neighbouring source

wooden barrier12 cm

straight waves

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1.1 What phenomenon is observed here?

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1.2 Define this phenomenon.

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1.3 Draw a sketch of waves moving through the opening.

1.4 Use a sketch to illustrate how this pattern (in Question 1.3) will be affected if the gap is decreased to 6 cm.

1.5 Use a sketch to illustrate how the pattern (in Question 1.3) will change if the wavelength is increased to 3 cm.

2 A ripple tank is set up with water. Two wooden blocks are placed to produce a narrow gap. A water wave is produced by a vibrator, moves towards the opening and goes through it. A diffraction pattern is formed on the other side of the opening. This pattern can be explained using Huygens’ Principle.

Sample



2.1 Write down Huygens’ principle.

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2.2 If the gap is widened, how will the pattern change? Give a reason for your answer.

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2.3 If the wavelengths of the waves are decreased, how will the pattern change? Give a reason for your answer.

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3 A ripple tank is set up with water. Three wooden blocks are placed in the tank so that there are two gaps of equal size. A water wave is produced with a vibrator and approaches the openings and travels through it. Interference occurs on the opposite side of the barriers.3.1 Define interference.

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3.2 The following pattern is observed.

P

S

RQ

crestSample



3.2.1 What type of interference occurs at point Q? Give a reason for your answer.

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3.2.2 What type of interference occurs at point R? Give a reason for your answer.

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3.2.3 What type of interference occurs at point S? Give a reason for your answer.

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2.3.3 Diffraction of light wavesWe have looked at the diffraction of water waves and now we are going to investigate the diffraction of light. Diffraction and interference are unique properties of waves. If diffraction and interference occur in light, then this will prove that light is a wave.

Experiment 14 Date:Aim: To investigate light moving through a single slit.

Apparatus: • A light bulb with a straight filament• A glass slide with a single slit (Paint a glass slide with black

paint or hold it near a burning candle until it is completely black. Draw a straight line through the paint with a razor blade.)

• A combination colour filter (red and blue) or one blue filter and one red filter

Method: 1. Set up the lamp so the filament is vertical and darken the

room.2. Switch on the lamp.3. Hold the glass slide with the slit near your eye and look

through the slit at the filament. Observe the pattern that is formed.

4. Place the red filter, and then the blue filter, in front of the lamp and see what changes can be observed in the pattern.

Observations:1. White light

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red filter

blue filter

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2. Red light

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3. Blue light

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Questions:1. What is the difference between the diffraction pattern seen using red or blue light through a single slit?

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2. Does red light have a larger or smaller wavelength than blue light?

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3. Name the independent variable in this experiment.

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4. Name the dependent variable in this experiment.

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5. Which factors are kept controlled during this experiment?

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6. What is the relationship between the width of the central band (degree of diffraction) and the wavelength of the light?

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Conclusions:________________________________________________________________________________

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Experiment 15 Date:Aim: To investigate the diffraction of light through slits of different widths.

Apparatus: • Two rectangular slides painted black• Blade• A lamp with a straight filament• Blue filter

Method:1. Use the slide from the previous experiment.2. Make a wider slit in the second slide.3. Set up the apparatus in the same manner as for the previous experiment.4. Place the blue filter in front of the lamp and look at the light through the slit.

Questions:1. What do you observe?

__________________________________________________________________________

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2. Replace the slide with the narrow slit with the slide with the wider slit. What do you observe?

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3. What is the difference between the diffraction pattern when observing light through a narrow and a wider slit?

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4. Name the independent variable in this experiment.

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5. Name the dependent variable in this experiment.

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6. What are the controlled variables in this experiment?

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7. What conclusion can be drawn from this experiment?

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8. What is the relationship between the width of the central band (degree of diffraction) and the width of the slit?

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The following is observed in the previous experiments:1. Waves bend around the sides of a slit. Diffraction occurs when waves move through a narrow slit. On the outside edges, interference occurs, as the wavefronts interfere with one another. A bright central band is observed, with alternating dark and bright bands on either side.

the higher the crest, the higher the intensity, therefore the brighter the colour band

screen

dark band (1st minimum)

dark band (2nd minimum)

central colour band (maximum)Sample

Interference Diffraction

Diffraction:

Wavefront:

Huygens’ principle:

Degree of diffraction is affected by

Diffraction of light waves:

Bright bands:

Darker bands:

Wave nature of light:

Constructive Destructive

2D AND 3D WAVEFRONTS

Sample

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6DPSOHMarina Schmidt • Lida Smithdocscientia.co.za/images/stories/pdf/Gr11_Physics_WB_2016.pdf · 1.6.4 Static friction ( f S) 32 1.6.5 Kinetic friction (f K ... Experiment 4 46