MS.RAJA ELGADFY/ELECTROMAGENETIC PAPER3

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1 MSRAJA ELGADFY/ELECTROMAGENETIC PAPER3 1- In Fig 91, A and B are two conductors on insulating stands Both A and B were initially uncharged X Y A B Fig 91 (a) Conductor A is given the positive charge shown on Fig 91 (i) On Fig 91, mark the signs of the charges induced at end X and at end Y of conductor B [1] (ii) Explain how these charges are induced [3] (iii) Explain why the charges at X and at Y are equal in magnitude [1] (b) B is now connected to earth by a length of wire Explain what happens, if anything, to (i) the charge at X, [1] (ii) the charge at Y [2] [Total: 8]

2 MSRAJA ELGADFY/ELECTROMAGENETIC PAPER3 2- (a) Fig 81 shows a bar magnet suspended by a spring over a coil The coil is connected to a sensitive centre-zero millivoltmeter spring magnet coil sensitive centre-zero millivoltmeter Fig 81 (i) The lower end of the magnet is pushed down into the upper end of the coil and held at rest During the movement, an emf is induced in the coil The meter shows a deflection to the right and then returns to zero Explain why this emf is induced [1] (ii) State what happens to the needle of the meter when 1 the magnet is released from rest and is pulled up by the spring, [1] 2 the magnet continues to oscillate up and down, moving in and out of the coil with each oscillation [1]

3 MSRAJA ELGADFY/ELECTROMAGENETIC PAPER3 (b) Fig 82 shows a transformer 240 V mains coil P 8000 turns coil S 60 V lamp Fig 82 The primary coil P, connected to the 240V mains supply, has 8000 turns The secondary coil S supplies 60V to a lamp (i) Calculate the number of turns in the secondary coil (ii) 1 The current in the primary coil is 0050 A Calculate the power input to the transformer number of turns = [2] power = [1] 2 90% of the power input to the transformer is transferred to the lamp Calculate the current in the lamp current = [2] [Total: 8]

4 MSRAJA ELGADFY/ELECTROMAGENETIC PAPER3 3- Fig 91 shows two separate coils of wire wound around an iron core primary secondary coil coil iron core Fig 91 An ac supply is connected across the primary coil and a 12V lamp is connected across the secondary coil The lamp glows with normal brightness (a) State the name of the device shown in Fig 91 [1] (b) Explain why there is a current in the lamp [4] (c) (i) The coil connected to the lamp has 450 turns The emf of the ac supply is 240V Calculate the number of turns on the coil connected to the ac supply number of turns = [2] (ii) A 240V dc supply is used instead of the 240V ac supply Tick one box to indicate what happens to the lamp glows more brightly glows with the same brightness glows less brightly does not glow [1] [Total: 8]

5 MSRAJA ELGADFY/ELECTROMAGENETIC PAPER3 4- (a) Fig 101 shows the cross-section of a wire carrying a current into the plane of the paper For Examiner s Use Fig 101 On Fig 101, sketch the magnetic field due to the current in the wire The detail of your sketch should suggest the variation in the strength of the field Show the direction of the field with arrows [3] (b) Fig 102 shows part of a model of a dc motor B axis A C X Y D Fig 102 A loop of wire ABCD is placed between the poles of a magnet The loop is free to rotate about the axis shown There is a current in the loop in the direction indicated by the arrows (i) On Fig 102, draw arrows to show the directions of the forces acting on side AB and on side CD of the loop [1]

6 MSRAJA ELGADFY/ELECTROMAGENETIC PAPER3

7 MSRAJA ELGADFY/ELECTROMAGENETIC PAPER3 (ii) With the loop in the position shown in Fig 102, explain why the forces on AB and CD cause the loop to rotate about the axis (iii) [1] The ends X and Y of the loop are connected to a battery using brushes and a splitring commutator State why a split-ring commutator is used [2] [Total: 7] 5- (a) Describe an experiment that shows how a magnet can be used to produce a current in a solenoid by electromagnetic induction Sketch and label the arrangement of apparatus you would use

8 MSRAJA ELGADFY/ELECTROMAGENETIC PAPER3 For Examiner s Use [3] (b) Fig 81 represents a transformer with primary coil P and secondary coil S, wound on an iron core There is an alternating current in coil P iron core P S Fig 81 (i) State what happens in the iron core as a result of the alternating current in P [2]

9 MSRAJA ELGADFY/ELECTROMAGENETIC PAPER3 (ii) Tick the box next to the correct description of the current in S higher frequency ac For Examiner s Use same frequency ac lower frequency ac rectified dc constant dc [1] (iii) Coil P has 50 turns of wire, an applied voltage of 12V, and a current of 050 A Coil S has 200 turns Calculate the current in S Assume the transformer is 100% efficient current = [3] [Total: 9]

10 MSRAJA ELGADFY/ELECTROMAGENETIC PAPER3 6- A simple motor is made in a school laboratory A coil of wire is mounted on an axle between the poles of a horseshoe magnet, as illustrated in Fig 91 coil B C N S A D springy contacts (brushes) + battery Fig 91 (a) At the instant illustrated in Fig 91, the coil ABCD is horizontal and the battery is connected as shown (i) For this position, state the direction of the force on AB and the direction of the motion of AB force on AB direction of motion of AB [1] (ii) Explain why BC does not contribute to the turning force on the coil [1]

11 MSRAJA ELGADFY/ELECTROMAGENETIC PAPER3 (b) At the instant when the coil is vertical, the springy contacts do not, in fact, make contact with the ends of the coil Describe and explain what happens to the coil [2] (c) The motor in Fig 91 does not rotate very quickly The designer of a commercial motor is required to produce a faster-rotating motor Suggest one change that could be made to increase the speed of the motor [1] [Total: 5]

12 MSRAJA ELGADFY/ELECTROMAGENETIC PAPER3 7- (a) In Fig 81, a magnet is moving towards one end of a solenoid connected to a sensitive centrezero meter During this movement a current is induced in the solenoid S N Fig 81 Suggest three possible changes to the system in Fig 81 that would increase the induced current [3] (b) Fig 82 shows a transformer P is the primary coil S is the secondary coil The coils are wound on an iron core P S Fig 82 P has 200 turns and S has 800 turns The emf induced across S is 24V The current in S is 050 A The transformer operates with 100% efficiency

13 MSRAJA ELGADFY/ELECTROMAGENETIC PAPER3 Calculate (i) the voltage of the supply to P, (ii) the current in P voltage = [2] current = [2] [Total: 7]

14 MSRAJA ELGADFY/ELECTROMAGENETIC PAPER3 8- Fig 91 is a sketch of some apparatus, found in a Science museum, which was once used to show how electrical energy can be converted into kinetic energy When the switch is closed the wheel starts to turn switch metal supports + dc supply S N S N magnet metal spoked wheel small dish of mercury magnet wood base Fig 91 (a) Explain why the wheel turns when the switch is closed [2] (b) On Fig 91, draw an arrow to show the direction of rotation of the wheel [1]

15 MSRAJA ELGADFY/ELECTROMAGENETIC PAPER3 (c) The dc motor is another way to convert electrical energy into kinetic energy In the space below, draw a labelled diagram of a dc motor Examiner s Use [3] (d) Describe how the split-ring commutator on an electric motor works [2] [Total: 8]

16 MSRAJA ELGADFY/ELECTROMAGENETIC PAPER3 9 Fig 91 is a block diagram of an electrical energy supply system, using the output of a coalfired power station For Examiner s Use

17 MSRAJA ELGADFY/ELECTROMAGENETIC PAPER3 9 Fig 91 is a block diagram of an electrical energy supply system, using the output of a coal- fired power station tra ns mi ssi on power station output step-up output step-down output at 1100 V transformer at V transformer at 240 V consumer n u m b e r F i g 9 1 (a) Suggest one possible way of storing surplus energy when the demand from the consumers falls below the output of the power station [1] (b) State why electrical energy is transmitted at high voltage (c) [1] A transmission cable of resistance R carries a current I Write down a formula that gives the power loss in the cable in terms of R and I [1] (d) The step-up transformer has 1200 turns on the primary coil Using the values in Fig 91, calculate the number of turns on its secondary coil Assume that the transformer has no energy losses o f t u r n s =

18 MSRAJA ELGADFY/ELECTROMAGENETIC PAPER3 (e) The input to the step-up transformer is 800 kw Using the values in Fig 91, calculate the current in the transmission cables, assuming that the transformer is 100% efficient secondary coil For Examiner s Use current = [3] [Total: 8] 10 Fig 101 shows the basic parts of a transformer primary coil X input output Y Y Fig 101 (a) Use ideas of electromagnetic induction to explain how the input voltage is transformed into an output voltage Use the three questions below to help you with your answer What happens in the primary coil? What happens in the core? What happens in the secondary coil?

19 MSRAJA ELGADFY/ELECTROMAGENETIC PAPER3 [5] (b) State what is needed to make the output voltage higher than the input voltage [1]

20 MSRAJA ELGADFY/ELECTROMAGENETIC PAPER3

21 MSRAJA ELGADFY/ELECTROMAGENETIC PAPER3 (c) The core of this transformer splits along XX and YY Explain why the transformer would not work if the two halves of the core were separated by about 30 cm [1] (d) A 100% efficient transformer is used to step up the voltage of a supply from 100 V to 200 V A resistor is connected to the output The current in the primary coil is 04 A Calculate the current in the secondary coil current = [2]

22 MSRAJA ELGADFY/ELECTROMAGENETIC PAPER3 11 (a) Name the process that causes a potential difference across a solenoid due to the movement of a nearby magnet [1] (b) Fig 111 shows a solenoid connected to a centre-zero voltmeter, M A bar magnet is held with its N-pole close to one end of the solenoid solenoid N M Fig 111 (i) The magnet is pushed into the solenoid, and then brought to rest with its N-pole just inside the solenoid Describe the movement of the pointer of the meter M [2] (ii) The magnet is now pulled to the left out of the solenoid, at a higher speed than in (i) Compare the movement of the pointer of the meter with that seen in (i) [2] [Total: 5]

23 MSRAJA ELGADFY/ELECTROMAGENETIC PAPER3 12- Fig 101 shows a coil of wire rotating steadily in the magnetic field between the poles of a permanent magnet The current generated in the coil is to pass through resistor R rotation of coil coil N S A B C D R Fig 101 (a) The apparatus in Fig 101 is part of an ac generator What is connected between the ends A and B of the coil and the connections C and D? [1] (b) (i) On Fig 102, sketch a graph to show the variation with time of the current through R [1] current 0 time Fig 102 (ii) On Fig 102, show the time T corresponding to one complete rotation of the coil [1] (iii) State two ways in which the graph would be different if the coil spins at a faster rate 1 2 [2] (c) Suggest what could be connected between C and R so that the current in R is always in the same direction [1] [Total: 6]

24 MSRAJA ELGADFY/ELECTROMAGENETIC PAPER3 13 (a) Fig 101 shows a wire PQ placed between the poles of a magnet There is a current in wire PQ For Examiner s Use

25 MSRAJA ELGADFY/ELECTROMAGENETIC PAPER3 13 (a) Fig 101 shows a wire PQ placed between the poles of a magnet There is a current in wire PQ N P Q S Fig 101 (i) (ii) On Fig 101, sketch lines with arrows to show the direction of the magnetic field between the poles of the magnet [1] The force on PQ is into the paper Draw an arrow on PQ to show the direction of the current [1] (b) The wire PQ in Fig 101 is replaced by a narrow beam of β-particles travelling from left to right (i) Suggest a suitable detector for the β-particles [1] (ii) State the direction of the force on the β-particles [1] (iii) Describe the path of the β-particles in the space between the poles of the magnet [1] (iv) State what happens to the air molecules along the path of the β-particles

26 MSRAJA ELGADFY/ELECTROMAGENETIC PAPER3 l : For Examiner s Use 6 ] 14- Fig 81 is the plan of a small apartment that has four lamps as shown 2 60W living room 100 W kitchen 60W bathroom Fig 81 Power for the lamps is supplied at 200V ac and the lamps are all in parallel (a) In the space below, draw a lighting circuit diagram so that there is one switch for each room and one master switch that will turn off all the lamps Label the lamps as 60W or 100W [3] (b) The 100W lamp is switched on Calculate (i) the current in the lamp, current = [2] (ii) the charge passing through the lamp in one minute

27 MSRAJA ELGADFY/ELECTROMAGENETIC PAPER3 charge = [2]

28 MSRAJA ELGADFY/ELECTROMAGENETIC PAPER3

29 MSRAJA ELGADFY/ELECTROMAGENETIC PAPER3 (c) The three 60W lamps are replaced by three energy-saving ones, that give the same light output but are rated at only 15W each Calculate For Examiner s Use (i) the total reduction in power, reduction in power = [1] (ii) the energy saved when the lamps are lit for one hour energy saved = [2] [Total: 10] 15- Alternating current electricity is delivered at V to a pair of transmission lines The transmission lines carry the electricity to the customer at the receiving end, where the potential difference is V This is shown in Fig 101 Each transmission line has a resistance of 3Ω V 3 Ω 3 Ω V

30 MSRAJA ELGADFY/ELECTROMAGENETIC PAPER3 Fig 101 (a) The ac generator actually generates at a much lower voltage than V (i) Suggest how the voltage is increased to V [1] (ii) State one advantage of delivering electrical energy at high voltage [1] (b) The power delivered by the generator is 55kW Calculate the current in the transmission lines current = [2] (c) Calculate the rate of loss of energy from one of the 3 Ω transmission lines rate of energy loss = [2]

31 MSRAJA ELGADFY/ELECTROMAGENETIC PAPER3

32 MSRAJA ELGADFY/ELECTROMAGENETIC PAPER3 (d) Calculate the voltage drop across one of the transmission lines For Examiner s Use (e) voltage drop = [2] Calculate the potential difference V at the receiving end of the transmission lines V = [2] [Total: 10] 16- Alternating current electricity is delivered at V to a pair of transmission lines The transmission lines carry the electricity to the customer at the receiving end, where the potential difference is V This is shown in Fig 101 Each transmission line has a resistance of 3Ω V 3 Ω 3 Ω V Fig 101 (a) The ac generator actually generates at a much lower voltage than V (i) Suggest how the voltage is increased to V [1] (ii) State one advantage of delivering electrical energy at high voltage [1] (b) The power delivered by the generator is 55kW Calculate the current in the transmission lines

33 MSRAJA ELGADFY/ELECTROMAGENETIC PAPER3 current = [2] (c) Calculate the rate of loss of energy from one of the 3 Ω transmission lines rate of energy loss = [2]

34 MSRAJA ELGADFY/ELECTROMAGENETIC PAPER3

35 MSRAJA ELGADFY/ELECTROMAGENETIC PAPER3 (d) Calculate the voltage drop across one of the transmission lines voltage drop = [2] (e) Calculate the potential difference V at the receiving end of the transmission lines V = [2] [Total: 10] 17- A transformer is needed to step down a 240 V ac supply to a 12 V ac output (a) In the space below, draw a labelled diagram of a suitable transformer [3] (b) Explain (i) why the transformer only works on ac, [1] (ii) how the input voltage is changed to an output voltage

36 MSRAJA ELGADFY/ELECTROMAGENETIC PAPER3 [2] (c) The output current is 15 A Calculate (i) the power output, power = [1] (ii) the energy output in 30 s energy = [1]

37 MSRAJA ELGADFY/ELECTROMAGENETIC PAPER3 18- Fig 111 shows a flexible wire hanging between two magnetic poles The flexible wire is connected to a 12 V dc supply that is switched off For Examiner s Use wire fixed here N flexible wire hanging between magnetic poles S + 12 V dc wire fixed here Fig 111 (a) Explain why the wire moves when the supply is switched on [2] (b) State the direction of the deflection of the wire [2] (c) When the wire first moves, energy is changed from one form to another State these two forms of energy from to [1]

38 MSRAJA ELGADFY/ELECTROMAGENETIC PAPER3 (d) Fig 112 shows the flexible wire made into a rigid rectangular coil and mounted on an axle magnetic pole For Examiner s Use axle N N coil magnetic pole S S axle UCLES /03/M/J/05

39 MSRAJA ELGADFY/ELECTROMAGENETIC PAPER3 Fig 112 (i) (ii) Add to the diagram an arrangement that will allow current to be fed into the coil whilst allowing the coil to turn continuously Label the parts you have added [1] Briefly explain how your arrangement works [2 19- Electromagnetic induction may be demonstrated using a magnet, a solenoid and other necessary apparatus (a) Explain what is meant by electromagnetic induction [2] (b) In the space below, draw a labelled diagram of the apparatus set up so that electromagnetic induction may be demonstrated [2]

40 MSRAJA ELGADFY/ELECTROMAGENETIC PAPER3 (c) Describe how you would use the apparatus to demonstrate electromagnetic induction [2] (d) State two ways of increasing the magnitude of the induced emf in this experiment 1 2 [2]

CLASSIFIED 5 MAGNETISM ELECTROMAGNETIC INDUCTION GENERATOR MOTOR - TRANSFORMER. Mr. Hussam Samir

CLASSIFIED 5 MAGNETISM ELECTROMAGNETIC INDUCTION GENERATOR MOTOR - TRANSFORMER Mr. Hussam Samir EXAMINATION QUESTIONS (5) 1. A wire perpendicular to the page carries an electric current in a direction