Electricity & Magnetism MCQ

The current in a kettle is 10 A and the kettle is protected by a 13 A fuse.

The owner of the kettle replaces the 13 A fuse with a 3 A fuse.

What happens when the kettle is switched on?

• The fuse melts and the kettle might be damaged.

• The fuse melts and the kettle is undamaged.

• The fuse does not melt and the kettle works correctly.

• The fuse does not melt but the kettle fails to work.

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?

• 20

• 30

• 600

• 12 000

A metal sphere is charged by induction.

There are four stages W, X, Y and Z in this process.

W a charged rod is brought near to the sphere

X the sphere is earthed

Y the charged rod is taken away from the sphere

Z the earth connection is removed

In which order are the four stages carried out?

• W → X → Y → Z

• W → X → Z → Y

• Z → W → X → Y

• X → Z → W → Y

Why is soft iron used for the core of an electromagnet?

• Soft iron easily becomes a permanent magnet.

• Soft iron is a good electrical conductor.

• Soft iron is a poor thermal conductor.

• Soft iron loses its magnetism when the current in the coil is switched off.

Diagram 1 shows two thin, uncharged strips of plastic.

Diagram 2 shows the same strips after they have been rubbed with a dry cloth.

Which row describes the charge on the strips after rubbing, and the force between the strips after rubbing?

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A lamp is to be connected in a circuit so that the potential difference (p.d.) across it can be varied from 0 to 6 V.

Which circuit would be most suitable?

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A bar magnet is held near a coil of wire. The coil is connected to a sensitive voltmeter.

The N-pole of the magnet is moved quickly towards the coil.

The voltmeter shows a reading of +10 mV.

The N-pole of the magnet is then moved slowly away from the same end of the coil.

The reading on the voltmeter is observed.

Which voltmeter reading is possible?

• –15 mV

• –5 mV

• 0 mV

• +5 mV

A simple wiring diagram for an electric cooker is shown.

Why is there a wire connecting the metal case of the cooker to earth?

• It improves the efficiency of the cooker.

• It prevents the metal case from becoming too hot when the cooker is left on.

• It reduces the risk of an electric shock if the live wire touches the metal case.

• The electric cooker will not switch on without it.

A cell has an electromotive force (e.m.f.) of 1.5 V.
What does this statement mean?

• The cell converts 1.0 J of energy when driving 1.5 C of charge round a complete circuit.

• The cell converts 1.5 J of energy when driving 1.0 C of charge round a complete circuit.

• The cell converts 1.5 J of energy per second when driving 1.0 C of charge round a complete circuit.

• The cell converts 1.5 W of power when driving 1.0 C of charge round a complete circuit.

An alternating current (a.c.) power supply is connected in series with a resistor R and a diode.

Which graph shows how the voltage V across the resistor R varies with time?

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