Electromagnetic Induction Practice Questions

The magnet is held stationary inside the coil.

State the reading on the ammeter and give a reason for your answer.

State two changes the student could make to increase the size of the induced current.

Name the type of transformer used at a power station to increase the potential difference before transmission.

Name the type of transformer used at a local substation before the electricity reaches homes.

Give one reason why electrical energy is transmitted across the national grid at a very high potential difference.

Which component makes the output of a generator direct current (d.c.)?

• A slip rings
• B an iron core
• C a split-ring commutator
• D a step-up transformer

State the type of current produced by an alternator.

State one change that would increase the peak potential difference produced by an alternator.

State whether this is a step-up or a step-down transformer. Give a reason for your answer.

Calculate the number of turns on the secondary coil.

Use an equation selected from the list of equations at the end of this paper.

............................................... turns

The laptop draws a current of $3.0\text{ A}$ from the secondary coil. The transformer is 100% efficient.

Calculate the current in the primary coil.

current = ............................................... A

The student then pulls the magnet back out of the coil at the same speed.

Describe the reading on the ammeter as the magnet is pulled out.

Describe and explain the magnetic field produced by the induced current in the coil as the north pole of the magnet enters the coil.

State one other change the student could make, apart from changing the direction of movement, that would reverse the direction of the induced current.

Explain how the microphone converts the pressure variations in a sound wave into a varying current in a circuit.

Explain how a loudspeaker converts a varying current into a sound wave.

State which graph shows the output from a dynamo.

Explain how the dynamo produces this output. Refer to the split-ring commutator in your answer.

The coil of the generator producing Graph A is now rotated at twice the speed.

Describe two changes to Graph A.

Explain why the voltmeter reads $0\text{ V}$ while the switch stays closed.

At the instant the switch is closed, the voltmeter needle flicks and then returns to zero.

Explain why.

State the purpose of the iron core.

Explain how rotating the coil generates a potential difference.

Give two changes to the alternator that would increase the potential difference it generates.

Transformers are used in the national grid. Explain why it is important that the generators in power stations produce alternating current.

An alternator consists of a rectangular coil of wire that is rotated between the poles of a magnet. The ends of the coil are connected to slip rings that press against carbon brushes.

Explain how the alternator produces an alternating potential difference, and how the peak value and the frequency of the output can be increased.

Calculate the current in the transmission cables.

current = ............................................... A

Calculate the power dissipated in the transmission cables.

power = ............................................... W

An older line transmits the same $250\text{ MW}$ of power at $132\text{ kV}$ through cables of the same total resistance.

Calculate the power dissipated in these cables and compare your answer with the value in part (b).

Explain why a current is induced in the copper tube as the magnet falls, but not in the plastic tube.

Explain, in terms of the magnetic field produced by the induced current, why the magnet falls much more slowly through the copper tube.

The student repeats the experiment with a magnet of the same size and mass but of greater strength.

State and explain the effect on the time taken for the magnet to fall through the copper tube.