O LevelPhysicsCambridgeExam Questions4. Electricity & Magnetism4.4 Practical Electricity

Practical Electricity (Cambridge O Level Physics)

Exam Questions

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4.4 Practical Electricity

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4.4 Practical Electricity

1a
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A teacher uses a power supply in a metal case. The circuit for the power supply includes a fuse.

(i)
Draw the electrical symbol for a fuse.
[1]
 
(ii)

The metal case of the power supply is earthed. A fault occurs and a live wire touches the metal case.

 

Explain how earthing the metal case protects the teacher.

[3]

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1b
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The power supply circuit includes a transformer. Its input voltage is 240 V. There are 960 turns on the input coil and 64 turns on the output coil.

Calculate the output voltage of the transformer.

 
 
output voltage = ..................................................... V 

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2a
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Fig. 8.1 shows a circuit containing a 230 V a.c. supply connected to a television and two lamps. 

q8-cie-ol-physics-specimen-paper-2-sq

Fig. 8.1

In normal operation, both switches are closed. The power supplied to each lamp is 40 W and the power supplied to the television is 120 W.

Calculate, in normal operation:

(i)
the total number of kilowatt-hours (kW h) of energy supplied to the circuit in 1.0 hour

 
number of kW h = .......................................................... [1]

(ii)
the current in each lamp.


current = ....................................................... A [2]

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2b
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Explain why the switches are placed in the live wire and not in the neutral wire.

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2c
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State one advantage of connecting the two lamps in parallel in this circuit.

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