Electricity and Magnetism 4 Electricity and …...2010/10/04 · Electricity and Magnetism 16. On a stormy day, a large, positively-charged cloud is above a tree. An electrical charge

Electricity and Magnetism

4 Electricity and Magnetism 1. Simple phenomena of magnetism 2. Electrical quantities 3. Electrical circuits 4. Dangers of electricity 5. Electromagnetic effects 6. Cathode ray oscilloscope 1. The diagram shows part of a magnetic relay.

M is part of the core of the magnet. L is part of the armature which is attached to the core when a current flows through the coil. S is a stud which stops the armature being attracted too strongly.

Which line of the table gives the best materials for M, L and S ?

2. Which diagram correctly shows the electric field between two charged spheres ?

3. An electrical quantity is defined as ‘the energy converted by a source in driving a unit charge round a complete circuit’. What is this quantity called ? A. current B. electromotive force C. potential difference D. power

4. The diagram shows an electrical circuit.

Which pair of readings is obtained when a suitable power supply is connected between X and Y ?

5. The diagram shows part of an electric circuit.

What is the current in the 2 resistor ? A. 0.6 A C. 3.0 A B. 1.2 A D. 6.0 A

6. An electric heater consists of a heating

element mounted on a metal reflector. The reflector is connected to earth.

IGCSE Physics 1 Namrata David Publications


Where should the switch for the heating element be connected ? A. between the earth wire and the reflector B. between the live wire and the heating

element C. between the live wire and the neutral wire D. between the neutral wire and the heating

element 7. Each of the diagram below is a cross-section

through two parallel current –carrying conductors. Which diagram correctly shows the magnetic field pattern formed by the currents in the two conductors ?

8. The number of turns between each pair of

output terminals of a transformer is shown in the diagram.

Between which two terminals will the output be 12 V ? A. P and Q B. Q and R C. R and S

D. P and R

9. What is the part of a simple d.c motor that reverses the direction of current through the coil every half-cycle ? A. the armature B. the brushes C. the commutator D. the slip rings

10. A wire hangs between the poles of a magnet. When there is a current in the wire, in which direction does the wire move ?

11. The diagram shows a metal bar swinging like

a pendulum across a uniform magnetic field. The motion induces as e.m.f between the ends of the bar.

Which graph represents this e.m.f during one complete oscillation of the bar, starting and finishing at P ?



12. Why is electrical energy usually transmitted at

high voltage ? A. As little energy as possible is wasted in

the transmission cables B. The current in the transmission cables is

as large as possible C. The resistance of the transmission cables

is as small as possible D. The transmission system does not require

transformers

13. Diagram 1 shows the oscilloscope trace produced by an input of 2V at 50 Hz.

Diagram 2 shows the trace from a different input on the same oscilloscope

. What is the value of the new input ? A. 1 V at 50 Hz B. 2 V at 25 Hz

C. 2 V at 100 Hz D. 4 V at 50 Hz

14. The electric circuit shown is used to study the

charging of a capacitor C

The neon lamp lights when the p.d across the capacitor C reaches 110 V. The capacitor C then discharges , the lamp goes out and the p.d. across C slowly increases once more. What id the effect of increasing the resistance of R ? A. the lamp lights up and goes out at the

same rate B. the lamp lights up and goes out less

frequently C. the lamp lights up and goes out more

frequently D. the lamp will not go out at all

15. Four different substances are tested by using

each as the core of an electromagnet. The number of paper clips each holds is recorded when there is a current in the electromagnet and when the current is switched off.

Which substance is the best for making the core of a transformer ?



16. On a stormy day, a large, positively-charged cloud is above a tree. An electrical charge is induced on the tree as charged particles flow through it.

What is the charge induced on the tree and how do the charged particles move ?

17. End X of a metal rod attracts the N-pole of a

compass needle. What does this show about the rod ? A. it could be made of copper but is not

permanently magnetized. B. it could be made of copper with a S-pole

at X C. it could be made of steel but is not

permanently magnetized D. it could be made of steel with a N-pole at

X

18. The diagram shows two resistors connected in series with a cell.

Which statement defines the potential difference across XY ?


A. the power needed to drive a unit charge through the cell

B. the power needed to drive a unit charge between X and Y

C. the work done in driving a unit charge through the cell

D. the work done in driving a unit charge between X and Y

19. Which two resistor combinations have the

same resistance between X and y ?

A. P and Q B. P and S C. Q and R D. R and S

20. In order to turn off both lamps, which is the safest switch position ?

21. The diagram shows a beam of electrons entering a magnetic field.


What is the effect of the magnetic filed on the electrons ? A. they are deflected into the plane of the

diagram B. they are deflected out of the plane of the

diagram C. they are deflected towards the bottom of

the diagram D. they are deflected towards the top of the

diagram

22. A student pushes the N-pole of a bar magnet into the end Q of a long solenoid and observes a deflection to the right on the sensitive ammeter.

What will produce a deflection in the same direction ? A. pulling the N-pole out of end Q B. pulling the S-pole out of end P C. pushing the N-pole into end P D. pushing the S-pole into end P

23. A simple a.c generator produces an alternating e.m.f as shown.

24. A step down transformer changes 240 V a.c

to 12 V a.c. There are 600 turns on the primary coil.

How many turns are on the secondary coil ?

A. 20 C. 600 B. 30 D. 12 000



25. What are high voltages and low currents used to transmit electrical energy over long distances ? A. to increase the electromagnetic radiation B. to increase the speed at which electrons

move C. to reduce heat loss from the power line D. to reduce the resistance of the power line

26. A variable potential divider has a sliding

contact S that can be moved between end P and end Q. It is connected to a constant 6 V power supply , as shown below.

What happens gradually from 6 V to 0 V A. it deceases gradually from 6 V to 0 V B. it rises gradually from 0 V to 6 V C. it stays constant at 0 V D. it stays constant at 6 V

27. A capacitor C charges when it is connected to

a d.c. power supply.

Which arrows show the direction of the conventional current when the capacitor is charging ?

A. 1 and 3 B. 1 and 4 C. 2 and 3 D. 2 and 4

28. Four plotting compasses are placed near a bar magnet. You may ignore any effects of the Earth’s magnetic field. In which position does the compass appears like this,

29. The diagram shows a positively charged acetate strip and a negatively charged polythene strip that are freely suspended.

Two rods X and Y are bought up in turn to

these two strips. Rod X attracts the acetate strip but repels the polythene strip. Road Y does not repel either the acetate strip or the polythene strip.

Which type of change is on each rod ?

30. A cell is connected to a resistor.

What is the e.m.f of the cell equal to ? A. the potential difference across the resistor

for each unit of current B. the power produced in the circuit for each

unit of charge that passes C. the work done in the circuit for each unit

of charge that passes D. the work done in the circuit for each unit

of current 31. A cell is connected in series with an ammeter

and a lamp. The current is 1 A.

In which circuit, using identical cells, lamps and ammeters, is the current reading 2 A ?



32. Which circuit contains a cell, a light-emitting diode and a fixed resistor ?

33. In each of the circuit below, a short circuit occurs. In which circuit would the fuse blow and make the circuit safe to repair ?

34. An alternating current is passed through a wire stretched between the poles of a magnet.

Which way will the wire move ?

A. left and right B. right only C. up and down D. up only

35. X and Y are wires carrying electric current at right angles to the page. P, Q and R are plotting compasses. Any effect of the Earth’s magnetic field has been ignored.

What is true about the direction and size of the currents ?

36. A girl turns the handle of a small a.c. generator four times each second. The generator produces a maximum output voltage of 0.5 V.



Which of these following graphs best shows this ?

37. Which statement about the action of a transformer is correct ? A. an e.m.f. is induced in the secondary coil

when an alternating voltage is applied to the primary coil.

B. An e.m.f is induced in the secondary coil when there is a steady direct current in the primary coil

C. The current in the secondary coil is always larger than the current in the primary coil

D. The voltage in the secondary coil is always larger than the voltage in the primary coil.

38. Electric energy is transmitted at high alternating voltages. What is not a valid reason for doing this ? A. at high voltage, a.c. is safer than d.c B. for a given power, there is a lower current

with a higher voltage C. there is a smaller power loss at higher

voltage and lower current D. the transmission lines can be thinner with

a lower current

39. The diagram shows some of the important parts of the tube of a cathode-ray oscilloscope.

Which change in voltage results in the position of the spot on the screen moving towards the top ?

A. decreasing V1 B. decreasing V3 C. increasing V2 D. increasing V3

40. A thermistor is connected in a circuit with a 6 V cell, a 3000 resistor and a voltmeter, as shown. The graph shows how the resistance of the thermistor varies with temperature.

What is the temperature of the thermistor when the voltmeter reads 2 V ? A. 20 C C. 60 C B. 40 C D. 80 C



41. The diagram show an iron nail in four different situations. In which diagram will the nail become an induced magnet ?

42. The diagram shows parts of a loudspeaker.

Which type of current is passed through the coil and why?

43. In an electrostatics experiment , a plastic rod is rubbed with a cloth. The cloth becomes negatively charged. Which diagram shows the charge on the rod, and describes the movement of charge ?

44. An electrical quantity is defined as ‘ the energy converted by a source in driving a unit charge round a complete circuit.’ What is this quantity called ?

A. current B. electromotive force C. potential difference D. power

45. The diagram shows the current I/voltage V graph for a length of resistance wire.

Where can Ohm’s law be applied to the wire ? A. at Y only C. from X to Y B. at Z only D. from X to Z



46. Diagram 1 shows a resistor connected to a battery, an ammeter and a voltmeter. The ammeter reading is 0.5 A and the voltmeter reading is 3.0 V. A second identical resistor is now connected in parallel with the first resistor , as shown in diagram 2. What are the ammeter and voltmeter readings in the circuit shown in diagram 2 ?

47. How much energy is converted in a resistor of 5.0 carrying a current of 2.0 A for 10 seconds ? A. 4.0 J C. 100 J B. 25 J D. 200 J

48. A permanent magnet moving up and down on the end of a spring induces an e.m.f. in a coil.

Which factor, on its own, would decrease the maximum value of the induced e.m.f. ?

A. increasing the number of turns in the coil

B. increasing the strength of the magnet

C. raising the coil D. raising the support of the spring

49. Two parallel wires carry currents in the same direction.

Which diagram shows the magnetic field around each wire and the direction of the force on each wire ?

50. Why is a transformer used to connect a

generator in a power station to a long distance transmission line ?

A. to decrease the voltage and decrease the current

B. to decrease the voltage and increase the current

C. to increase the voltage and decrease the current

D. to increase the voltage and increase the current

51. The table shows part of the colour code for

resistors.

Which resistor has a value of 4700 ?



52. The diagram shows a brass rod and an iron rod beside each other at the time of a rectangular coil.

What happens when a d.c. current passes through the coil ?

A. only the brass rod is magnetized B. only the iron rod is magnetized C. the two rods attract each other D. the two rods repel each other

53. Four metal rods are placed, in turn, inside a coil of copper wire.

Each rod is used to pick up as many paper clips as possible. The current is then switched off. The table gives the results of the experiment. Which rod is the most suitable core for a coil in a circuit breaker ?

54. Which factors will both increase the resistance

of a wire in a circuit ?

55. Two uncharged metal spheres, not touching

one another, are suspended by means of cotton thread. A positively charged rod is brought near.

Which diagram shows what happens to the spheres ?



56. Which graph best represents how current I varies with voltage V in a component in which the resistance increases as the current increases.

57. At which point in the circuit is the current the smallest ?

58. The diagram shows a circuit.

The ammeter has negligible resistance. What is the resistance of the resistor R ?

A. 0.5 B. 1.5 C. 5 D. 6

59. The diagram show the Forces F between two wires carrying current out of the page. The magnetic fields close to the wires are also shown.

Which diagram is correct ?

60. The diagram shows the circuit for a hair-dryer.

The fan has a power rating of 0.1 kW and the heaters each have a rating of 0.4mkW. The cost of electricity is 8 cents/K Wh. What is the cost of running the dryer for two hours with switches P and Q closed and switch R is open ?

A. 1.6 cents B. 3.2 cents C. 6.4 cents D. 8.0 cents

61. In a d.c motor, the coil is wound on a soft iron cylinder. Why is soft iron used ? A. to increase the strength of the magnetic

field B. to increase the weight of the coil C. to insulate the coil from the magnet D. to prevent the coil from spinning too

quickly




62. Which circuit shows the correct positions for the fuse and the switch in the lighting circuit of a house ?

63. The diagram shows how a magnet and a coil

may be used to induce an electric current.

How could the ammeter reading be increased ?

A. move the coil more quickly B. put resistor in series with the

ammeter C. turn the magnet round, then move

the coil D. use a coil with more turns

64. Four processes are used to charge an isolated metal sphere. P The sphere is earthed by touching it. Q The earth connection is removed from the sphere R A charged rod is brought close to the sphere S The charged rod is removed In which order should these processes be carried out to charge the sphere ? First last A. P Q R S B. P R S Q C. R P Q S D. R S P Q

5. A wave form is displayed on a cathode-ray

and the time-base settings

6oscilloscope. The length of three cycles of the waveform is 6 m. The vertical gain are shown on the diagram.

What is the time taken for one cycle of the

C. 4 ms

66. r a ent magnet can be demagnetized by

iagram shows the most effective

waveform ? A. 1 ms B. 2 ms D. 6 ms

A pe m nusing a solenoid and switching the current on then off. Which dmethod of producing demagnetization ?

67. wo insulated metal spheres X and Y are Tinitially in contact. While a positively charged rod is near X the spheres are moved apart. After this action X has a negative charge.


The charge on Y will be A. negative and smaller than that on X B. negative and the same size as that on X C. positive and smaller than that on X D. positive and the same size as that on X

68. which combination of identical resistors gives

the lowest total resistance ?

69. The diagram shows a voltmeter adapted to measure a range from 0-100 mV. The voltmeter is measuring the potential difference in a circuit.

What is the reading on the voltmeter ?

A. 0.06 mV B. 0.6 mV C. 6 mV D. 60 mV

70. In an a.c. elecrtic circuit in a house, the switch for any device is always connected to the ‘live’ lead.

Why is this ? A. no current ever flows in the neutral lead of

the device B. the device will be shorted if the switch is

in the earth lead C. the device can never be switched off if the

switch is in the neutral lead D. the device can only be isolated ( made

safe) id the switch is in the live lead

71. A house-owner replaced a failed fuse for the lights of the house. When the lights were switched on, the new fuse also failed. The house-owner then used another fuse with a higher rating than the previous two. Why was this not a sensible thing to do ? A. fuses allow the circuit to work only if the

rating is exactly right B. the fuse has already melted because the

rating was too high C. using a fuse with too high rating would

cause electric shocks D. a fuse with a higher rating might allow the

circuit to work, but the fault would not be corrected

72. The diagram shows a beam of electrons

entering a magnetic field. The direction of the field is into the page.

What will be the initial direction of the deflection of the electrons as the beam passes through the field ? A. into the page B. out of the page C. towards the bottom of the page D. towards the top of the page

73. The diagram shows a two-pole single-coil

electric motor.



The spilt-ring commutator reverses the current in the coil as it rotates. How many times is the current reversed if the coil is rotated once ? A.1 B. 2 C. 3 D. 4

74. Which statement about the action of a transformer is correct ? A. an alternating current always flows in the

secondary coil when an alternating voltage is applied to the primary coil

B. the current in the secondary coil is larger than the current in the primary coil

C. an e.m.f. is induced in the secondary coil when an alternating voltage is applied to the primary coil

D. an e.m.f. is induced in the secondary coil when a steady direct current flows in the primary coil

75. The diagram shows a trace on an

oscilloscope set at 5 V/cm on the vertical axis.

What is the maximum value of the potential difference being measured ?

A. 1.5 V C. 7.5 V B. 3.0 V D. 15 V

76. A 24 resistor is to be connected in series with a 12 V battery. What is the power loss in the resistor ?

A. 0.5 W C. 12W B. 6W D. 24 W

77. Which of the following will prove that a metal bar is a permanent magnet ?

A. it attracts another magnet B. it attracts both ends of a compass

needle C. it conducts electricity D. it repels another magnet

78. A positively charged rod is brought closed to an insulated metal sphere. Which diagram best shows the induced charges on the sphere ?

79. How could the unit of potential difference , the

volt, also be written ? A. A/s C. C/J B. C/A D. J/C

80. X and Y are lamps with filaments made from the same material. The filament of lamp X is thicker and shorter than that of lamp Y. When connected to the mains and switched on , which is the brighter lamp and which lamp has the larger resistance ?

Brighter lamp Larger resistance

A X X B X Y C Y X D Y Y

81. A 1.0 resistor and a 2.0 resistor in

series across a 12 V d.c. supply. What is the current in the circuit ?

A. 0.25 A C. 6.0 A B. 4.0A D. 12 A

82. The cable to an electric fan becomes so worm that the live wire makes electrical contact with the metal case. The case is earthed. The plug to the fan contains a 5 A fuse. There is a current of 4 A when the fan works normally. What will happen ? A. the current will run to earth and the fuse

will not be affected. B. The fuse will melt and switch off the

circuit.



C. The metal case will become live and dangerous

D. The metal case will become very hot 83. A small heater operates at 12 V, 2A.

How much energy will it use when it is run 5 minutes ?

A. 30 J C. 1800 J B. 120J D. 7200 J

84. Which of the following has no effect on the size of the turning effect on the coil of an electric motor.

A. the size of the current in the coil B. the direction of the current in the

coil C. the number of turns in the coil D. the strength of the magnetic field

85. Why is electricity transmitted along power lines at very high voltages? A. to reduce the resistance of the cables B. so that transformers can be used C. to make sure that the current is the same

all the way along the power lines D. to reduce loss of energy

86. A small coil is connected to a galvanometer

as shown below. When the magnet is allowed to fall towards the coil, the galvanometer pointer gives a momentary deflection to the right of the zero position.

The magnet moves through the coil and , as it falls away from the coil, the galvanometer pointer A. gives a continuous reading to the left B. gives a momentary deflection to the left C. gives a momentary deflection to the right D. gives a continuous reading to the right

87. A simple a.c. generator produces a voltage

that varies with time as shown.

Which graph shows how the voltage varies with time when the generator rotates at twice the original speed ?

88. The diagram shows a circuit.

What are the components X and Y ?

89. The following trace is shown on the screen of an oscilloscope when it is connected to a



transformer. The scale is set at 5 V per centimeter.

What is the value of the peak voltage ? A. 4 V C. 10 V B. 5 V D. 20 V

90. The diagram shows a circuit with a potential

divider joined in series with a fixed resistor.

What are the minimum and maximum readings that can be obtained on the voltmeter when the potential divider is adjusted ?

91. A bar magnet is broken into three parts X,Y

and Z.

Which diagram shows the poles in X,Y and Z ?

92. A wire of length 1.0 m has a resistance of 2.0

. When connected to a cell , the current in the wire is 3.0 A.

A 2.0 m length of the same wire is connected to the same cell.

What is the resistance of the wire and the current in it ?

93. In the circuit shown, at which point is the current is smallest ?



94. The potential difference between the ends of a conductor is 12 V. How much electrical energy is converted to other forms of energy in the conductor when 100 C of charge flows through it ?

A. 0.12 J C. 88 J B. 8.3 J D. 1200 J

95. An electrical engineer connects a diode to a

radio so that : If the battery is connected the right way round the radio works, If the battery is connected the wrong way there is no current. Which diagram is correct ?

96. Which circuit shows how the heater in an electric iron and a fuse should be connected to a mains electricity supply ?

97. A small coil is connected to a sensitive

ammeter. The ammeter needle can move to either side of the zero position. When the magnet is allowed to fall towards the coil, the ammeter needle moves quickly to the right of the zero position.

The magnet moves through the coil. How does the ammeter needle moves as the magnet falls away from the coil ?



A. it does not move B. it gives a steady reading to the right C. it moves quickly to the left of the zero

position and then returns to zero D. it moves quickly to the right of the zero

position and then returns to zero

98. A catode-ray oscilloscope is connected to an a.c generator. a wave is shown on the screen.

What is the effect on the trace if the generator’s speed of rotation s doubled ?

99. In which circuit will a lamp glow more brightly

when less light shines on a light-dependent resistor ?

100. The diagram shows the design of a

cathode-ray oscilloscope tube. There is a conatsnt potential difference across the deflection plates.

Which change increases the deflection of the spot on the screen ? A. decreasing the distance from the

deflection plates to the screen B. increasing the length of the deflection

plates C. increasing the potential difference

between cathode and anode D. increasing the separation of the deflection

plates 101. A student tries to magnetize a short steel

rod. which of these tests will show that he has been successful ? A. both ends of a permanent magnet attracts

the rod B. one end of a permanent magnet repels

the rod C. the rod picks up a small piece of paper D. when freely suspended, the rod points in

any direction 102. Why can birds stand on an overhead high

voltage transmission line without suffering any harm ? A. their bodies have a very high resistance B. their feet are very good insulators C. the spaces between their feathers act as

insulators D. they are not connected to earth.

103. The diagram below shows a cell

connected in series with an ammeter and there resistors ( 10 , 20 , 30 ). The circuit can be completed by a moveable contact M.

When M is connected to X, the ammeter reads 0.6 A.



What is the ammeter reading when M is connected to Y ?

A. 0.1 A C. 0.3A B. 0.2 A D. 0.6 A

104. In the circuit shown , the battery lights up all four lamps. When one of the lamp filaments melts, the other three lamps stay on. Which lamp filament melts ?

105. A combined bathroom unit of a heater and a lamp is controlled by one switch. The unit contains a 2 kW heater and a 100 W lamp. In one week, the lamp uses 1 kWh of electrical energy. How much electrical energy is used by the heater alone ?

A. 2 kWh C. 10kWh B. 4 kWh D. 20kWh

106. An electric kettle is plugged in and

switched on. The fuse in the plug blows immediately. Which single fault could cause this ?

A. the earth wire is not connected to the kettle

B. the live wire and neutral wire connections in the plug are swapped around

C. the live wire touches the metal case of the kettle

D. the wire connected to the plug are too thin

107. A coil, carrying a current, is arranged

within a magnetic field. The coil experiences forces that can make it move.

In which direction does the coil move? A. along the magnetic field B. from X to Y C. out of the paper D. turns about the axis

108. A magnet is pushed horizontally towards a coil of insulated wire, inducing an e.m.f in the coil.

In which direction does the induced e.m.f. make the coil move ? A. away from the magnet B. towards the magnet C. downwards D. upwards

109. A step-up transformer with 100 %

efficiency has an input voltage of 3 V and an input current of 2 A.

Under these conditions , what output voltage and output current could be obtained ?

110. Why is a reed relay used in a switching circuit ? A. to switch on a small current using a large

current B. to switch on a small voltage using a large

voltage C. to switch on a large current using a small

current D. to switch on a large voltage using a large

current 111. a potential divider consists of an LDR and

a resistor connected to a 6 V battery.



What should be the resistance of the LDR for the output to be 3 V ?

A. 0 B. Between 0 and 10 000 C. 10 000 D. More than 10 000

112. A current in a solenoid creates a magnetic filed.

What is the effect on the magnetic field at the point P of using a larger current in the opposite direction ?

113. A metal ring screens a piece of equipment from magnetic field.

Which metal should be used for the ring, and why ?

114. Two insulated and uncharged metal spheres X and Y are touching. While a positively charged rod is near X, the spheres are moved apart. After this action , X has a negative charge.

What will be the charge on Y ? A. negative and smaller than that on X B. negative and the smaller size as that on X C. positive and smaller than that on X D. positive and the same size as that on X

115. A wire has a resistance of 8 . A second

wire, made of the same material, has half the length and twice the cross-sectional area. What is the resistance of the second wire ?

A. 1 C. 8 B. 2 D. 16

116. Two resistors of 6 and 12 are arranged in parallel. A p.d. is connected across the terminals X and Y. the current through the 6 resistor is 4 A.

What is the current in the ammeter ?

A. 4 A C. 8 A B. 6 A D. 12 A

117. Which of the following would cost the

least if operated from the same voltage supply ? A. a 5000 W electric cooker used for 1

minute B. a 1000 W electric fire used for 10 minutes C. a 500 W electric iron used for 1 hour D. a 100 W lamp used for 1 day



118. A copper wire is held between the poles of a magnet.

The current in the wire can be reversed. The poles of the magnet can also be changed over. In how many of the four directions shown can the force act on the wire ? A. 1 C. 3 B. 2 D. 4

119. A transformer has more turns on the

secondary coil than on the primary. The graph shows how the input voltage varies with time.

Which graph, drawn to the same scale as the input graph, shows how the output voltage varies with time ?

120. The diagram shows a coil in a magnetic field.

When the coil is part of a d.c motor, what must be connected directly to X and Y ?

A. d.c. supply B. slip rings C. soft-iron core D. split-ring commutator

121. Why is electrical energy usually transmitted at high voltage ?

A. as little energy as possible is wasted in the transmission cables

B. the current in the transmission cables is as large as possible

C. the resistance of the transmission cables is as small as possible

D. the transmission system does not require transformers

122. The diagram shows the output waveform

of an a.c. generator as displayed on a cathode-ray oscilloscope. The horizontal scale is 5 ms/cm.

What is the time for one complete rotation of the coil of the generator ?

A. 5 ms C. 20 ms B. 10 ms D. 30 ms

123. A capacitor can be made to store energy by connecting it to a d.c. power supply.

Along which paths do electrons flow as the capacitor starts to charge ? A. from X to plate 1 only B. from X to plate 1 and from plate 2 to Y C. from Y to plate 2 and from plate 1 to X D. from Y to plate 2 only



124. The diagram shows a model railway signal.

What does the end P do when the switch is closed ?

A. it goes down and stays down B. it goes up and stays up C. it goes down and then returns to

its original position D. it goes up and then returns to its

original position.

125. Which part of a vedio tape recording system does not rely on magnetic material for its operation ?

A. the drive motor B. the power lead C. the transformer D. the video tape

126. A positively charged insulated metal sphere is brought close to, but not touching, a similar uncharged metal sphere.

Which diagram shows the charge distribution on the spheres ?

127. Under which condition does Ohm’s law apply ?

A. the current must be constant B. the power must be constant C. the temperature must be constant D. the voltage must be constant

128. a battery is used to light a 24 W electric lamp. The battery provides a charge of 120 C in 60 s.

What is the potential difference across the bulb ?

A. 5 V C. 24 V B. 12 V D. 120 V

129. A student sets up the circuit shown.

The currents measured with the ammeters are shown. Which equation is correct ?

130. The following circuit is set up.

What is the reading on ammeter ?

A. 0.33 A C. 0.67 A B. 0.50 A D. 1.0 A



131. Energy is represented by the letter E, current by I, power by P, charge by Q, p.d. by V and time by t. Which pair of equations is correct ?

A. E = It and P = VIt B. E = VQ/t and P = VI C. E = VIT and P = VI D. E =VQ and P = VI/t

132. The case of an electric fan is earthed.

The plug to the fan contains a 5 A fuse. There is a current of 4 A when the fan works normally. The cable to the fan becomes so worn that the live wire makes electrical contact with the metal case. What happens ?

A. the current flows to earth and fuse is not affected

B. the fuse melts and switches off the circuit

C. the metal case becomes live and dangerous

D. the metal case becomes very hot 133. The diagram shows the a beam of

electrons entering a magnetic filed . The direction of the field is into the page.

In which direction are the electrons deflected ? A. Into the page B. Out of the page C. Towards the bottom of the page D. Towards the top of the page

134. Which single coil motor will have the

largest turning effect ?

135. The diagram shows transformers and cables used to transmit electrical energy over log distances.

How does transformer X affect the voltage and the current from the power station ?

136. In the circuit shown, all lamps are identical and all cells are identical. The resistance of the coil of the reed switch is negligible.

One cell lights one lamp to normal brightness. What is the brightness of the lamps when switch Y is closed ?

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137. Which diagram best shows the pattern of field lines around a bar magnet ?

138. Which materials are suitable to make a permanent magnet and the core of an electromagnet ?

139. Which two electric quantities are measured in volts ?

A. current and e.m.f. B. current and resistance C. e.m.f. and potential difference D. potential difference and

resistance

140. Which of the following pieces of copper wire has the greatest electrical resistance ?

141. A 20 resistor and a 10 resistor are connected in parallel.

What is their combined resistance ?

A. less than 10 B. 10 C. 20 D. More than 20

142. The diagram shows an incomplete circuit.

Which component should be connected in the space to make the lamp light ?

143. Why are the electric lamps in a house lighting circuit normally connected in parallel ?

A. the current in every circuit must be the same

B. the lamps are always switched on and off at the same time

C. the voltage across each lamp must be the mains voltage

D. when one of the lamps blows, all the others go out

144. In the circuit shown , one of the fuses

blows and all the lamps go out. Which fuse blows ?



145. When electricity is transmitted over long distances, energy is wasted. How can the wasted energy be kept as small as possible ? A. keep the current in the transmission

lines as large as possible B. keep the power supplied to the

transmission lines as large as possible C. keep the resistance of the transmission

lines as large as possible D. keep the voltage supplied to the

transmission lines as large as possible 146. The diagram shows a transformer.

What is the voltmeter reading ?

A. 1.2 V C. 120V B. 12 V D. 1200 V

147. The diagram shows part of a circuit used to switch street lamps on and off automatically.

What is the effect on the light-dependent resistor (LDR) when it gets dark ?

148. An alternating potential difference (p.d.) is applied to the Y-plates of a cathode-ray oscilloscope. The time-base is turned off. Which of the following pattern would appear on the screen ?

149. A student wishes to use a magnetizing coil to make a permanent magnet from a piece of metal.

Which metal should she use ?

A. aluminum B. copper C. iron D. steel

150. A metal rod XY is placed near a magnet. End X is attached when it is placed near to the north pole of the magnet, and also when it is placed near to the south pole.



How does end Y behave when it is placed, in turn, near to the two poles of the magnet ?

151. When the potential difference (p.d.)

across a piece of resistance wire is changed, the current through the wire also changes. The temperature of the wire is kept the same. Which graph shows how the p.d. and current are related ?

152. Two faulty ammeters and two perfect

ammeters are connected in series in the circuit shown.

The readings on the ammeters are

A1 2.9 A A2 3.1 A A3 3.1 A A4 3.3 A

Which two ammeters are faulty ? A. A1 and A2 B. A1 and A4 C. A2 and A3 D. A3 and A4

153. Which electrical component would not normally be found in a battery-operated torch ( flash light) ?

154. A student makes four circuits.

In which circuit are both lamps protected by the fuse ?

155. Four lamps are labeled ’60 W 240V’ In which circuit are the lamps connected so that they all work at normal brightness ?



156. The diagram shows a transformer with an

alternating voltage of 100 V applied to the primary coil.

What is the voltage produced across the secondary coil ?

A. 50 V C. 200 V B. 100 V D. 8000 V

157. How can a permanent magnet be demagnetized ?

A. cool the magnet for a long time B. hit the magnet repeatedly with a

hammer C. leave the magnet in a coil which

carries direct current D. pass a small current through the

magnet 158. The diagram shows a solenoid connected

to a sensitive voltmeter.

Which of the following would give a zero reading on the voltmeter ?

A. holding the magnet stationary inside the solenoid

B. moving the magnet away from the solenoid

C. moving the magnet towards the solenoid

D. moving the solenoid towards the magnet

159. The diagram below shows the screen of a

cathode-ray oscilloscope tube.

The tube is [laced between a pair of charged plates. Which diagram shows the new position of the spot ?



160. An electrical component X is placed in water, as shown.

When the temperature of the water is increases, the reading on the ammeter increases. What is component X ?

A. capacitor B. a light-dependent resistor C. a reed relay D. a thermistor

161. A student connects two lamps in the circuit shown.

Which switches must he close to light both lamps ? A. 1 and 2 C. 1 and 3 B. 1,2 and 3 D. 2 and 3

162. An electromagnet is used to separate

magnetic metals from non-magnetic metals. Why is steel unsuitable as the core of the electromagnet ?

A. it is a good conductor of electricity B. it forms a permanent magnet C. it has a high density D. it has a high thermal capacity

163. Which circuit shows a voltmeter is

connected to measure the potential difference across the cell ?

164. A polythene rod repels an inflated balloon hanging from a nylon thread. What charges must the rod and the balloon carry ?

A. the rod and the balloon carry opposite charges.

B. The rod and the balloon carry like charges

C. The rod is charged but the balloon is not

D. The balloon is charged but the rod is not

165. An electrical component is to be placed in

the circuit at Z, to allow the brightness of the lamp to be varied from bright to dim.

What should be connected at Z ?

166. Which electric quantity is measured in farad ?

A. current B. capacitance C. current and resistance D. potential difference



167. The circuit shown contains four lamps and

three switches.

Which switches must be closed to light only lamps 1 and 3 ?

A. switch 1 only B. switch1 and switch 2 only C. switch1 and switch 3 only D. switch2 and switch 3 only

168. The diagram shows a torch containing

two 2 V cells, a switch and a lamp.

What is the circuit diagram for the torch ?

169. Which statement is correct ? A. a fuse is included in a circuit to prevent

the current becoming too high B. a fuse should be connected to the neutral

wire in plug C. an electric circuit will only work if it

includes a fuse D. an earth wire is needed to prevent the

fuse blowing

170. A straight wire carrying a current produces a magnetic field. Which diagram shows the correct shape of the field ?

171. A student carries out an experiment to

see the effect of a magnetic field on a wire carrying a current. The wire moves upwards as shown.

What should the student do to make the wire move downwards ?

A. change the direction of the current

B. move the poles of the magnet closer together

C. send a smaller current through the wire

D. use a stronger magnet

172. A beam of cathode rays passes through an electric field between two parallel plates.

In which direction is the beam deflected ?

A. into the page



B. out of the page C. towards the bottom of the page D. towards the top of the page

173. Which material is used for the core of an electromagnet ?

A. aluminium B. copper C. iron D. steel

174. A brass rod is positioned in an east-west

direction and plotting compass is placed at each end.

Which diagram shows the positions of the needles of the plotting compasses ?

175. How many of the following materials conduct electricity ? Aluminium Silver Iron Plastic

A. 1 C. 3 B. 2 D. 4

176. In which circuit does the voltmeter read the potential difference across the lamp ?

177. In the circuit below , X and Y are identical 6 V lamps.

What happens when the switch is closed ?

A. X lights more brightly than Y B. Y lights more brightly than X C. X and Y light with equal

brightness D. Neither X nor Y light

178. The diagram shows a circuit with three ammeters X, Y and Z.

Which set of readings is possible ?



179. A lamp is to be connected in a circuit so that the p.d. across it can be varied from 0 to 6 V. Which circuit would be most suitable ?

180. A student makes the circuit shown.

The fuse has blown and stopped the circuit. What could have caused this ?

A. the current rating of the fuse was too high

B. the current was too large C. the lamp was loose D. the voltage was too small

181. Which graph shows the output voltage from a simple a.c generator ?

182. A transformer has 50 turns on its primary coil and 100 turns on its secondary coil. An a.c voltage of 25.0 V connected across the primary coil.

What is the voltage across the secondary coil ?

A. 12.5 V C. 175. V B. 50.0V D. 200 V

183. Two circuits are set up as shown. The iron rods are placed close together, and are free to move.



What happens to the size of the graph at X when switch S is closed ? A. it decreases B. it decreases then increases C. it increases D. it does not change

184. The diagram shows a simple cathode-ray tube. Which part emits the electrons ?

185. A student investigates which end of a magnetic compass needle is attracted to bar magnet. What does the investigation show ? A. both ends of the compass needle are

attracted by the north pole of the magnet

B. both ends of the compass needle are attracted by the south pole of the magnet

C. one end of the compass needle are attracted by the north pole and the other end by the south pole

D. the compass needle is not attracted by either end of the magnet

186. From which materials are the coil and the

core of an electromagnet made ?

187. What are the symbols used for the units of current and resistance ?

188. When a plastic comb is placed next to a small piece of aluminium foil hanging from a nylon thread, the foil is repelled by the comb. Why is this ?

A. the comb is charged and the foil is uncharged

B. the comb is uncharged and the foil is charged

C. the comb and the foil have charge of opposite signs

D. the comb and the foil have charge of the same sign

189. Which symbol represents an electrical

component used to store energy ?

190. Four lamps and four switches are connected to a power supply as shown in the circuit diagram. When all the switches are closed, all the lamps are lit. When one of the switches is opened, only ne lamp goes out. Which switch is opened ?

191. Four resistors and an ammeter are connected to a battery as shown. The ammeter reads 2 A. Which of the four labeled points in the circuit is the only one where the current is less than 2 A.



192. Why is a fuse used in an electrical circuit in a house ?

A. to increase the circuit resistance B. to keep the power used to a

minimum value C. to prevent a short-circuit from

occurring D. to stop the cables from carrying

too much current

193. An electric power tool is being used outdoors in a shower of rain. What is the greatest hazard to the user ?

A. the cable gets hot and causes burns

B. the circuit-breaker cuts off the current

C. the current passes through water and causes a shock

D. the tool rusts

194. A current-carrying coil in a magnetic field experiences a turning effect.

How can the turning effect be increased ?

A. increase the number of turns on the coil

B. reduce the size of the current C. reverse the direction of the

magnetic field D. use thinner wire for the coil

195. A transformer is to be used to produce a 6 V out put from a 24 V input.

What are suitable numbers of turns for coil X and for coil Y ?

196. A cathode –ray tube has an anode and an

earthed cathode. Which line in the table shows the charge and the temperature of the anode ?

197. Small particles of metal are scattered near a bar magnet to show the pattern of the magnetic field. Which metal is suitable ?

A. aluminium B. brass C. copper D. iron

198. A strong electromagnet is used to attract pins.

What happens when the current in the coil is halved ?

A. no pins are attracted B. fewer pins are attracted C. the same number of pins is

attracted D. many more pins are attracted



199. Four plotting compasses are placed near a bar magnet. Which plotting compass is shown in the correct direction ?

200. Four wires are made from the same material. Which wire has the greatest resistance ?

201. Which circuit is a variable potential divider

( potentiometer) ?

202. A plastic rod is rubbed with a dry cloth

and becomes positively charged. Why has the rod becomes positively

charged ?

A. it has gained electrons B. it has gained neutrons C. it has lost electrons D. it has lost neutrons

203. The circuit contains a relay.

When switch S is closed, what is the state of the lamps ?

204. Which diagram shows a circuit that will allow the lamps to be switched on and off independently ?

205. What is the symbol of fuse ?

206. A cable in a house is carrying too much current. What is the greatest danger ?

A. appliances not working B. electric shock C. fire D. low power



207. A coil is rotated steadily between the poles of a magnet. The coil is connected to an oscilloscope, which shows a graph of voltage output against time.

Which graph shows the voltage output against time ?

208. The diagram shows a lamp connected to

a transformer.

What is the potential difference across the lamp ?

A. 2.4 V C. 60 V B. 12 V D. 240V

209. A beam of cathode rays passing through

an electric field between two parallel plates.

In which direction is the beam deflected ?

A. into the page B. out of the page C. towards the bottom of the page D. towards the top of the page

210. A piece of magnetized steel is placed inside a coil of wire that has a large alternating current passing through it. The magnet is slowly moved out of the coil to position P.

How has the steel changed when it

reaches P ? A. it has become demagnetized B. there has been no change C. it has become a stronger magnet D. the poles have changed ends

211. In which circuit does the ammeter read the total current through both resistors ?



212. A permanent magnet is placed closer to a bar of soft iron PQ.

What happens ?

A. P becomes a north pole B. P becomes a south pole C. PQ does not become magnetized D. The poles of the magnet are

reversed

213. The table shows the voltage and current ratings for four light bulbs. Which bulb has the greatest resistance when used normally ?

214. In the following circuits, the resistors have the same value and the cells are identical. Which circuit has the smallest resistance ?

215. The diagram shows a circuit, with four possible positions to place a switch.

At which labeled point should a switch be placed so that lamp 1 remains on all the time and lamp 2 can be switched on and off ?

216. The device X in this circuit is designed to

cut off the electricity supply automatically if too much current flows.

What is device X ?

A. a fuse B. a relay C. a resistor D. an ammeter

217. A class room has four lights, each fitted with a lamp marked 240V, 100 W. Which circuit is most suitable for the class room ?

218. Charged particles are emitted from the cathode of an oscilloscope. What is the name and charge of these particles ?



219. Which graph shows the output of a simple a.c. generator ?

220. When the electric current in wire XY is in the direction shown, there is an upward force on the wire.

If the north and south poles of the magnet exchange positions, in which direction will the force on the wire act ?

A. downwards B. upwards C. to the left D. to the right

221. A steel bar is magnetized by stroking it

several times with the south pole of a magnet, as shown.

Which poles are formed at X and Y ?

222. Diagram 1 shows a potential divider

circuit containing two 100 resistors.

One of the resistors is changed to 90 , as shown in diagram 2.

How does the reading on the voltmeter change when this is done ?

A. it becomes zero B. it dearness a little C. it increases a little D. it stays the same

223. A steel ball on a horizontal wooden table

rolls near the north pole of a bar magnet that is lying on the table. Which diagram shows the most likely path of the ball, as seen from above the table ?



224. A student wants to find the resistance of resistor R using a voltmeter and an ammeter. Which circuit should the student use ?

225. Two very light, charged balls P an Q are hung, one above the other, from nylon threads. When a negatively charged plastic sheet is placed alongside them, P is repelled and Q is attracted.

What are the original charges on P and

on Q ?

226. Four students are asked to draw a circuit showing three lamps working in parallel, a cell, and a switch that controls all three lamps. Which student is correct ?

227. A 3.0 lamp and a 6.0 lamp are connected in series.

What is the total resistance of the combination ?

A. 0.5 C. 9.0 B. 2.0 D. 18.0

228. Why is a circuit breaker or fuse used in a mains electric circuit ? A. it allows spare current to be returned to

the mains. B. It improves the insulation of the wiring C. It protects the mains wiring from current

overload D. It saves energy by reducing the current



229. The diagram shows two ways in which

three lamps may be connected.

Which statement is correct ? A. if lamp Y breaks in circuit 1 , both the

other lamps will go out. B. if lamp Y breaks in circuit 2, both the other

lamps will go out. C. if lamp Y breaks in circuit 1, lamp Z will go

out, but lamp X will remain on D. if lamp Y breaks in circuit 2, lamp Z will go

out, but lamp X will remain on.

230. How is electricity transmitted over large distances and why is it transmitted in this way ?

231. In a cathode-ray tube, particles are given off from a hot cathode by thermo ionic emission. Which particles are given off ?

A. atoms B. electrons C. ions D. protons

232. When the thermistor in the circuit below is heated, the lamp becomes brighter.

Why does this happen ?

A. the resistance of the lamp decreases

B. the resistance of the lamp increases

C. the resistance of the thermistor decreases

D. the resistance of the thermistor increases

233. A circuit is set up with a gap between two

terminals X and Y. The four strips of material shown in the diagram are connected in turn across the gap. Which strip completes the circuit so that the lamp lights ?

234. A pupil measures the potential difference across a device and the current in it. Which calculation gives the resistance of the device ?

A. current + potential difference B. current potential difference C. potential difference current D. potential difference current

235. Which circuit could be used to find the resistance of resistor R ?



236. In a circuit shown, the reading on

ammeter 1 is 2 A.

What is the reading on ammeter 2 ? A. 0 A C. 2 A B. 1 A D. 4 A

237. In which position in the circuit shown should a switch be placed so that both lamps can be switched on or off at the same time ?

238. In the circuit shown, all the resistors are identical. Which circuit has the least resistance ?

239. Why are electric circuits often fitted with

fuses ? A. fuses break the circuit if the

current is too high B. fuses only allow the current

through in the correct direction C. fuses return any excess current to

earth D. fuses use up any spare current

240. A mains circuit can safely supply a current

of 40 A. A hair-drier takes 2 A. It is connected to the circuit by a lead which can carry up to 5 A. Which of these fuses would be best to use in the plug fitted to the hair-drier lead ?

A. 1 A fuse C. 10 A fuse B. 3 A fuse D. 50 A fuse

241. The diagram represents a transformer.

Which arrangement could be used to make the output voltage higher than the input voltage ?

242. A student sets up the apparatus shown in order to make a relay.

Which metal should be used to make the core ?

A. aluminium B. copper C. iron D. steel



243. Which particles are emitted in thermo

ionic emission ? A. electrons B. ions C. neutrons D. protons

244. How many of the following methods could

be used to demagnetize a piece of steel ? Heating it until it is red hot Pulling it from a coil that is carrying an alternating current Placing it in an east-west direction and hammering it Putting it in a coil which is carrying a direct current A. 1 C. 3 B. 2 D. 4

245. Two rods X and Y look the same.

The N pole of a magnet is brought close, in turn, to each end of both rods. The results of these four actions are shown in the table.

Which of the rods is a permanent magnet ?

A. neither of the rods B. both of the rods C. rod X only D. rod Y only

246. Which circuit should be used to find the

resistance of a lamp ?

247. The table shows the voltage and current ratings for four electric heaters. Which heater has the least resistance ?

248. Which component can store energy for use in time delay circuits ?

A. capacitor B. potentiometer C. resistor D. thermistor

249. When the circuit shown is connected with switch S open, the 6 V lamp glows.

What happens to the brightness of the lamp when switch S is closed ?

A. it becomes brighter B. it remains the same C. it becomes dimmer D. it goes off



250. Why are the electric lamps in a house

lighting circuit normally connected in parallel ? A. the current in every circuit must

be the same B. the lamps are always switched on

and off at the same time C. the voltage across each lamp

must be the mains voltage D. when one of the lamps blows, all

the others go out

251. In the circuit shown, one of the fuses blows and all the lamps go out Which fuse blows ?

252. Which arrangement may be used to step up a voltage ?

253. The diagrams show a straight wire carrying a current into the paper. Which diagram shows the magnetic field pattern due to this current ?

254. A magnet is suspended from a spring so that it can move freely inside a coil which is connected to a sensitive centre-zero ammeter.

What does the ammeter show when the magnet vibrates slowly up and sown ?

A. a reading constantly changing from left to right and right to left

B. a steady reading to the left C. a steady reading to the right D. a steady zero reading



255. Charged particles are emitted from the cathode of an oscilloscope. What is the name and the charge of these particles ?

256. A student uses three small plotting compasses to investigate the magnetic filed around a bar magnet. Which diagram shows the directions in which the compass needles point ?

257. The ends of three metal rods are tested by holding end Q of rod 1 close to the others in turn .

The results are as follows. End Q : attracts end R Attracts end S Attracts end T Repels end U. Which of the metal rods is a magnet ?

A. rod 1 only B. rod 1 and rod 2 only C. rod 1 and rod 3 only D. rod 3 only

258. A student wishes to measure the electromotive force ( e.m.f.) of a battery and the potential difference (p.d.) across a resistor. She has the resistor, the battery and some connecting wires. What else does she need ?

A. a voltmeter only B. an ammeter only C. an ammeter and a voltmeter D. a force meter(Newton meter) and

a volt meter

259. Which particle does not experience a force due to an electric filed ?

A. alpha particle B. electron C. neutron D. proton

260. A student uses a length of wire as a resistor. He discovers that the resistance of the wire is too small. To be certain of making a resistor of higher value, he should use a piece of wire that is

A. longer and thicker B. longer and thinner C. shorter and thicker D. shorter and thinner

261. Which graph shows how the resistance of a thermistor changed with temperature ?



262. In the circuit below, one of the lamps

breaks, causing all the other lamps to go out. Which lamp breaks ?

263. Circuit breakers are used with electrical appliances as safety devices. Which description is correct for a circuit-breaker ?

264. The graph shows the voltage input to a

step-down transformer.

Which diagram shows the voltage output from the transformer ?

265. An electric heater is connected to the mains using insulated copper wires. The wires become very warm.



What can be done to prevent so much heat being produced in the connecting wires ?

A. use thicker copper wires B. use thinner copper wires C. use thicker insulation D. use thinner insulation

266. The diagram shows an electrical device.

What is this electrical device ?

A. a d.c. motor B. an a.c. generator C. a magnetizing coil D. a transformer

267. Particles are emitted by a heated cathode in a cathode-ray tube.

What are these particles ?

A. atoms B. electrons C. neutrons D. protons

268. Three charged balls P,Q and R are suspended by insulated threads. Ball P is negatively charged.

What are the charges on Q and on R ?

269. The circuit shows a current I in a resistor of resistance R.

Which line gives possible values of I and

of R ?

270. The circuit shows in the diagram contains

an unknown component X, hidden in a box. The voltage-current graph for X is as shown.

What is the component X ?

A. a capacitor C. a metallic resistor B. a closed switch D. an open switch



271. Four lamps are connected in a circuit as shown in the diagram. Each lamp is designated to operate at 12 V.

The circuit is now switched on. Which statement is correct ?

D. voltmeter 1, voltmeter 2 and voltmeter 3

274. A householder asks an electrician to

install a mains electrical socket in her bathroom so that she may use a hairdryer there. The electrician refuses to do this because it would be dangerous. Why would installing the socket be dangerous ? A. the current drawn by the hairdryer would

cause overheating in the cables B. the handling of electrical equipment in

damp conditions could cause an electric shock. A. each lamp can be switched off

independently C. The hot air produced by the hairdryer would cause the fuse to melt B. if one lamp breaks all the others

will stay alight. D. The temperature in the bathroom would damage the insulation C. The current is the same in all the

lamps. D. The lamps will all light at normal

brightness 275. How is electricity transmitted over large

distances and why is it transmitted in this way ?

272. The diagram shows a battery connected

to three identical resistors. Four ammeters A, B, C and D are connected in the circuit. Which ammeter shows the smallest reading ?

276. Which parts of an a.c. generator slide past each other when the generator is working ?

A. brushes and coil B. coil and magnets C. magnets and slip rings D. split rings and brushes 273. In the circuit shown, the switch is closed

for a long time, then opened.

Immediately after the switch is opened, which voltmeters will read zero ?

277. The diagram shows a cathode-ray tube.

What must be done to deflect the electron beam upwards ?

A. Make X1 more positive than X2 B. Make X2 more positive than X1 A. voltmeter 1 only C. Make Y1 more positive than Y2 B. voltmeter 2 only D. Make Y2 more positive than Y1 C. voltmeter3 only


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