Physical Sciences Physics Grade 11 Textbook and Workbook Ronel Bernardo Hendry du Plessis Santie du Plessis Carlien Fanoy Elize Jones Patricia Lees-Rolfe Judy McDougall Karen Reynecke Marina Schmidt Lida Smith
Doc Scientia Posbus 7011 Ansfrere 1711 www.docscientia.co.za For any queries and feedback: info@docscientia.co.za Jacques Fanoy or Stephan Fanoy Office: 011 472 8728 Fax: 086 546 1423 ISBN: 978-1-920537-16-6 First edition December 2009 Revised edition December 2010; 2011 Second edition December 2012 Revised 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.
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. Scientia Doc
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: Activity Any activity that is done with pen and paper. Practical activity A simple investigation or experiment to understand the theory better. Experiment Examples Interesting facts Quick facts Summary Notes Case study Project Definitions and formulae Use your smartphone to activate the QR codes. Remember Enrichment Question paper The method of the experiment is given step by step, and you should follow it to get results. Experiments confirm the theory. OR It is expected of you to plan and carry out the experiment to obtain results.
INDEX Unit 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 ( f S ) 32 1.6.5 Kinetic friction (f K ) 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 Summary of Unit 2 96 Mind maps of Unit 2 98
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 Summary of Unit 3 112 Mind maps of Unit 3 113 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 Summary of Unit 1 164 Mind maps of Unit 1 166 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 Summary of Unit 2 186 Mind maps of Unit 2 188 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
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 Summary of Unit 1 230 Mind maps of Unit 1 233 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 Practical demonstration 2 241 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 Summary of Unit 2 252 Mind maps of Unit 2 256 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 Practical demonstration 3 274 Exercise 20 277 3.6 Cost calculations 280 3.7 Saving electricity 282 Exercise 21 283 Summary of Unit 3 285 Mind maps of Unit 3 288 Question paper 290 Information sheets 303 Work cited 305
UNIT 2 2D and 3D wavefronts KNOWLEDGE AREA: WAVES, SOUND AND LIGHT 2D AND 3D WAVEFRONTS Properties of waves Interference Refraction Diffraction of waves Huygens principle Diffraction of water waves Diffraction of light waves 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. Doc Scientia PHYSICS textbook and workbook - Grade 11 167
Properties of waves 2.1 Interference When 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 is a phenomenon in which two waves superimpose to form a resultant wave of greater or lower amplitude. 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. There are two types of interference: Constructive 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 + b Quick facts Coherent sources are sources that are in phase with each other. Destructive 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. a a b -b a + (-b) After interfering, the two pulses will continue with their original speed and amplitude. 168 PHYSICS textbook and workbook - Grade 11 Doc Scientia
2.2 Refraction When 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 Interesting facts Christiaan Huygens was a Dutch mathematician and scientist. In 1678 he proposed a way of explaining the behaviour of waves. 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. secondary wavefront original wavefront source The new wavefront is obtained by drawing a tangent to all the new little waves. original wavefront each of these points is a source (secondary source) of a circular little wave new wavefront constructive interference (crest with crest) secondary source new (secondary) wavefront destructive interference (crest with trough) Doc Scientia PHYSICS textbook and workbook - Grade 11 169
These circular waves undergo interference with each other. Where they interfere constructively, a new wavefront is formed. A wavefront is an imaginary line joining all the points in a wave that are in phase. wavefront 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 waves Huygens 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. 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. If a new tangent is drawn to each circle, a new wavefront is Crests overlap: constructive obtained. interference occurs. 170 PHYSICS textbook and workbook - Grade 11 Doc Scientia
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. wavefronts 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) Aim: crest trough To investigate the diffraction of waves. Apparatus: Ripple tank Two barriers Ruler to produce waves. destruction 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. Date: Doc Scientia PHYSICS textbook and workbook - Grade 11 171
Observations: 1. What happens when the wave hits a barrier? 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: 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. 172 PHYSICS textbook and workbook - Grade 11 Doc Scientia
opening wavefront 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 1 A ripple tank is set up with water. constructive interference: crest with crest from neighbouring source destructive interference: crest with trough from neighbouring source Date: 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. 12 cm wooden barrier straight waves Doc Scientia PHYSICS textbook and workbook - Grade 11 173
1.1 What phenomenon is observed here? 1.2 Define this phenomenon. 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. 174 PHYSICS textbook and workbook - Grade 11 Doc Scientia
2.1 Write down Huygens principle. 2.2 If the gap is widened, how will the pattern change? Give a reason for your answer. 2.3 If the wavelengths of the waves are decreased, how will the pattern change? Give a reason for your answer. 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. 3.2 The following pattern is observed. crest P Q S R Doc Scientia PHYSICS textbook and workbook - Grade 11 175
3.2.1 What type of interference occurs at point Q? Give a reason for your answer. 3.2.2 What type of interference occurs at point R? Give a reason for your answer. 3.2.3 What type of interference occurs at point S? Give a reason for your answer. 2.3.3 Diffraction of light waves We 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 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 Date: red filter blue filter 176 PHYSICS textbook and workbook - Grade 11 Doc Scientia
2. Red light 3. Blue light Questions: 1. What is the difference between the diffraction pattern seen using red or blue light through a single slit? 2. Does red light have a larger or smaller wavelength than blue light? 3. Name the independent variable in this experiment. 4. Name the dependent variable in this experiment. 5. Which factors are kept controlled during this experiment? 6. What is the relationship between the width of the central band (degree of diffraction) and the wavelength of the light? Doc Scientia PHYSICS textbook and workbook - Grade 11 177
Conclusions: Experiment 15 Aim: Date: 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? 2. Replace the slide with the narrow slit with the slide with the wider slit. What do you observe? 178 PHYSICS textbook and workbook - Grade 11 Doc Scientia
3. What is the difference between the diffraction pattern when observing light through a narrow and a wider slit? 4. Name the independent variable in this experiment. 5. Name the dependent variable in this experiment. 6. What are the controlled variables in this experiment? 7. What conclusion can be drawn from this experiment? 8. What is the relationship between the width of the central band (degree of diffraction) and the width of the slit? 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 central colour band (maximum) dark band (1 st minimum) dark band (2 nd minimum) screen Doc Scientia PHYSICS textbook and workbook - Grade 11 179
Interference Constructive 2D AND 3D WAVEFRONTS Destructive Diffraction: Wavefront: Huygens principle: Degree of diffraction is affected by Diffraction of light waves: Bright bands: Darker bands: Wave nature of light: Diffraction