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describe the shape of magnetic fields around a magnet and between two magnets discuss the magnetic effect of an electric current describe the shape of magnetic fields around current carrying wires in different situations explain why a current carrying wire experiences a force in a magnetic field
Hilbert Luke,Content Editors,Science Department,Subject Review Committee. Language Editor,Dr Mirzi L Betasolo,Course Format Editor. Elizabeth W Aimundi,GR 12 PHYS M4 TITLE,ELECTROMAGNETISM. IN THIS MODULE YOU WILL LEARN ABOUT,12 4 1 MAGNETIC FIELD AND FORCE DUE TO CURRENT. 12 4 2 ELECTROMAGNETIC INDUCTION,12 4 3 TRANSFORMERS AND POWER LOSSES IN. TRANSMISSION LINES,GR 12 PHYS M4 ACKNOWLEDGEMENT ISBN. Acknowledgement, We acknowledge the contribution of all Lower and Upper Secondary teachers who in. one way or another helped to develop this Course, Our profound gratitude goes to the former Principal of FODE Mr Demas Tongogo for. leading FODE towards this great achievement, Special thanks are given to the staff of the Science Department of FODE who played. active roles in coordinating writing workshops outsourcing of module writing and. editing processes involving selected teachers of Central Province and NCD. We also acknowledge the professional guidance and services provided through out. the processes of writing by the members of,Science Subject Review Committee FODE. Academic Advisory Committee FODE,Science Department CDAD. This book was developed with the invaluable support and co funding of the GO PNG. and World Bank,DIANA TEIT AKIS,Principal FODE,Flexible Open and Distance Education. Papua New Guinea,Published in 2017,Copyright 2017 Department of Education. Papua New Guinea, All rights reserved No part of this publication may be reproduced. stored in a retrieval system or transmitted in any form or by any. means electronic mechanical photocopying recording or any. other form of reproduction by any process is allowed without the. prior permission of the publisher, Printed by the Flexible Open and Distance Education. ISBN 978 9980 89 565 3,National Library Services of Papua New Guinea. GR 12 PHYS M4 CONTENTS,TABLE OF CONTENTS,Acknowledgement ISBN 2. Contents 3,Secretary s Message 4,MODULE 12 4 ELECTROMAGNETISM 5 72. Course Introduction 5,Learning Outcomes 6, 12 4 1 Magnetic Field and Force Due to Current 7 30. Magnets and Magnetic Fields 7 11,Forces Due to Current in Magnetic Field 12 17. AC and DC Electric Motors 18 30,12 4 2 Electromagnetic Induction 31 52. Current Induced in the Presence of a Magnetic Field 31 52. 12 4 3 Transformers and Power Losses in Transmission Lines 52 63. Transformers 52 58,Power Losses in Transmission Lines 59 63. Summary 64,Answers to Learning Activities 66 71,References 72. GR 12 PHYS M4 MESSAGE,SECRETARY S MESSAGE, Achieving a better future by individual students their families communities or the nation as. a whole depends on the kind of curriculum and the way it is delivered. This course is part of the new Flexible Open and Distance Education curriculum The. learning outcomes are student centred and allows for them to be demonstrated and. It maintains the rationale goals aims and principles of the National Curriculum and. identifies the knowledge skills attitudes and values that students should achieve. This is a provision by Flexible Open and Distance Education as an alternative pathway of. formal education, The Course promotes Papua New Guinea values and beliefs which are found in our. constitution Government policies and reports It is developed in line with the National. Education Plan 2005 2014 and addresses an increase in the number of school leavers. affected by lack of access into secondary and higher educational institutions. Flexible Open and Distance Education is guided by the Department of Education s Mission. which is fivefold, To develop and encourage an education system which satisfies the requirements of. Papua New Guinea and its people, To establish preserve and improve standards of education throughout Papua New. To make the benefits of such education available as widely as possible to all of the. To make education accessible to the physically mentally and socially handicapped as. well as to those who are educationally disadvantaged. The College is enhanced to provide alternative and comparable path ways for students and. adults to complete their education through one system two path ways and same learning. It is our vision that Papua New Guineans harness all appropriate and affordable technologies. to pursue this program, I commend all those teachers curriculum writers university lecturers and many others who. have contributed so much in developing this course. UKE KOMBRA PhD,Secretary for Education,GR 12 PHYS M4 INTRODUCTION. MODULE 12 4 ELECTROMAGNETISM,Introduction, Electromagnetism is a branch in physics which deals with electricity and magnetism and the. interaction between them It was discovered in the 19 th century and has extensive. application in today s world, Electromagnetism is basically the science of electromagnetic fields An electromagnetic field. is produced by objects which are charged electrically Radio waves infrared waves. ultraviolet waves and x rays are all electromagnetic fields in a certain range of frequencies. Electricity is produced by changing magnetic fields This phenomenon is also called. electromagnetic induction Electromagnetism is basically the work of an underlying force. known as the electromagnetic force This force can be seen when an electric charge is. moving This movement of electric charges produces magnetism It has been proved that. electricity can give rise to electromagnetism and vice versa A very clear example is that of a. transformer which we will look at later, Electromagnetism has numerous applications in today s world of science and physics The. very basic application of electromagnetism is in the use of motors The motor has a switch. that continuously switches the polarity of the outside of the motor. An electromagnet does the same thing We can change the direction by simply reversing the. direction of the current The inside of a motor has an electromagnet but the current is. controlled in such a way that the outside magnet repels it. Transformers are extremely useful engineering devices as they allow for the changing or. transforming of AC voltages not only in small construction circuits but also on an electrical. energy production and distribution level Mains distribution high voltage transformers are a. common sight on the poles of our electricity networks. A typical power supply grid system,GR 12 PHYS M4 OUTCOMES. Learning Outcomes, After going through this module you are expected to. define and explain a magnetic field, describe the shape of magnetic fields around a magnet and between two magnets. discuss the magnetic effect of an electric current. describe the shape of magnetic fields around current carrying wires in different. situations, explain why a current carrying wire experiences a force in a magnetic field. calculate the size of this force, calculate the force between parallel wires carrying a current. draw a diagram of a simple DC motor and explain how it works. calculate the size of the force on a current carrying conductor passing through the. magnetic field using the formula F BIL and F BIL sin. demonstrate experimentally that current is induced in a straight wire when moved. through a magnetic field, show experimentally that size of the induced current in a straight carrying conductor. depends on the length of the wire the strength of the field and speed of the wire in. the magnetic field, apply Lenz Law and Fleming s Left and Right hand Rules to explain the operation of. the AC and DC generators, define a transformer and explain its main principles of operation. do calculations of step up and step down ideal transformers. give advantages of AC generators over DC generators in power transmission. solve problems involving power losses and voltage drop across the transmission lines. Time Frame Suggested allotment time 10 weeks,This module should be completed within 10 weeks. If you set an average of 3 hours per day you should be able to complete the module. comfortably by the end of the assigned week, Try to do all the learning activities and compare your answers with the ones provided at the. end of the module If you do not get a particular question right in the first attempt you. should not get discouraged but instead go back and attempt it again If you still do not get it. right after several attempts then you should seek help from your friend or even your tutor. DO NOT LEAVE ANY QUESTION UNANSWERED,GR 12 PHYS M4 ELECTROMAGNETISM. 12 4 1 Magnetic Field and Force Due To Current, Whenever a current passes through a conductor a magnetic field is produced This can be. shown by placing a directional compass near a straight current carrying wire or conductor A. compass placed near a current carrying conductor will always point in the direction of the. magnetic field lines produced However a magnetic material like iron cobalt or nickel when. placed in the presence of the magnetic field will always experience a force acting on it. Magnets and Magnetic Field, The idea of magnetism was first discovered by the Chinese as early as 2500 BC They found. that certain minerals can attract pieces of iron When these minerals were allowed to be. suspended hung freely they will always point in the north to south direction Nowadays we. call these objects magnets A bar magnet has two poles the South Pole and North Pole. There are many examples of the uses of magnets in today s world Magnets are used in. dynamos motors radios TV refrigerator door locks and tape recorders among others. A magnetic field is a region where a magnet exerts a force This region is made up of lines of. forces This means that if a magnetic material like iron cobalt or nickel is placed in the. magnetic field it will experience a force acting on it. The pattern a magnet makes can be shown using iron filings or a directional compass. Figure 1 The magnetic field lines around a bar magnet. You will note from the diagram that the magnetic field starts from the North Pole and enter. into the South Pole The magnetic field is the strongest at the poles where the field lines are. closer together, When magnets are placed closer to each other their magnetic fields interact with each. other Very simple experiments can show us that when like poles N N or S S are held. closer to each other they tend to repel However unlike poles N S or S N attract each. other This brings us to the law of magnetism which states. Like poles repel and unlike poles attract,GR 12 PHYS M4 ELECTROMAGNETISM. Neutral point, Figure 2 The magnetic fields around unlike poles facing each other are almost uniform in strength. However between like poles there is a neutral point where the combined field strength is zero. You will have learnt in electricity that when a current passes through a conductor it. produces heat and light energies We will now learn how electricity produces some magnetic. effects The connection between electricity and magnetism has many important applications. in today s world, In electromagnetism this unit the current we are referring to is the conventional. current which flows from the positive terminal of the power supply. Consider a directional compass is allowed to settle in its normal north south direction When. a wire is placed over the compass and a current is allowed to flow the compass needle. deflects It is noticed that the compass needle is deflected at 90 0 to the wire i e east west. direction When the current is switched off the current needle returns to its original north. south direction This shows us that a wire carrying a current has a magnetic effect. Directional Directional,N compass N compass, Figure 3 a No current in the wire b Current passing through the wire. The magnetic effect can further be investigated using a vertical current carrying wire The. wire passes through a hole in a piece of cardboard which is placed horizontally When iron. fillings are sprinkled on the cardboard and tapped gently they arrange themselves in a. circular pattern,GR 12 PHYS M4 ELECTROMAGNETISM,directional. iron fillings,straight current,wire direction, Figure 4 The magnetic field around a straight wire. This circular pattern represents the magnetic field around the wire A compass needle can. also be used to find the direction of the magnetic field It is found that if the direction of the. current is reversed the direction of the magnetic field is also reversed. The direction of a magnetic field around a wire carrying a current is given by Fleming s Right. Hand Grip Rule This rule states that if you grip a straight wire with your right hand then. your extended thumb points in the direction of the current Your fingers wrapped around. the wire will point in the direction of the magnetic field lines. Figure 5 Applying the right hand grip rule to find the. direction of the magnetic field around a wire, The characteristics of the magnetic field produced by a current flowing in a straight wire. The magnetic field lines form a circular pattern, The magnetic field strength increases when current increases. The magnetic field strength is stronger near the wire and weaker further away. When the direction of the current is reversed the direction of the magnetic field is. reversed too,GR 12 PHYS M4 ELECTROMAGNETISM, We can view the direction of the current as represented by a point or as a cross. A point represents the current flow in an upward direction out of the paper It can. be seen as looking at a sharp point or tip of an arrow coming towards you. A cross represents the current flow in a downward direction into the paper like. looking at the tail end of an arrow away from you,Current in upward. Current in downward,out of page direction into page. Figure 6 a Current in upward direction b Current in downward direction. Now check what you have just learnt by trying out the learning activity below. Learning Activity 1 10 minutes, Answer the following questions on the spaces provided. 1 What is meant by the term magnetic field, 2 What sort of materials when placed in a magnetic field will experience a force. GR 12 PHYS M4 ELECTROMAGNETISM, 3 Draw the magnetic field patterns of the magnets shown below. a S N S N b N S S N, 4 Sketch the magnetic field pattern of a steady electric current flowing in a long straight. wire in the directions shown,Current flowing Current flowing into. out of paper paper,paper paper, Thank you for completing learning activity 1 Now check your work Answers are at the. end of the module,GR 12 PHYS M4 ELECTROMAGNETISM,Force Due To Current in a Magnetic Field. We have learnt earlier that when a current passes through a conductor a magnetic field is. produced However if the current carrying conductor is placed inside a magnetic field a. force is produced that will act on the conductor, The conductor experiences a force because the magnetic field around the conductor. interacts with the magnetic field of the magnet This causes weaker and stronger effects on. two sides of the conductor Thus the conductor will move in the direction of the weaker. wire moves, Figure 7 A force acts on a current carrying conductor in a magnetic field. The force causes the wire to move at right angles 900 to the magnetic field If you reverse. the direction of the current in the wire the direction of the force reverses This means that. the wire will move in the opposite direction, You must note that the direction of the current the magnetic field and the force must. always be at right angles to each other What we are trying to talk about here are three. physical quantities current magnetic field and the force We will try to see how these. quantities relate to each other in terms of their directions. From figure 7 above at least the direction of two quantities current and magnetic field. current and force or force and magnetic field must be known to predict the direction of the. third quantity The third quantity can be predicted using the Fleming s Left Hand Rule as. illustrated on the next page,GR 12 PHYS M4 ELECTROMAGNETISM. rust or force,irst finger, Figure 8 Fleming s Left Hand Rule indicates the link between force field. and current directions,The rule can be used as follows. The thumb and the first two fingers must be held at right angles 900 to each other. The thumb gives the direction of the force, The first finger gives the direction of the magnetic field and. The second finger gives the direction of the current. For example in figure 7 if the directions of the current and the magnetic field are known. then using the Fleming s Left Hand Rule we can very easily predict or identify the direction. of the force In this case the direction of the force is out of the page or moving upwards. When you apply the rule you must always remember, The magnetic field direction is always from the North Pole to the South Pole. The current direction is always from the positive terminal of the battery. The rule applies when the current magnetic field and force are at right angle to. each other, Now check what you have just learnt by trying out the learning activity on the next page.