A magnet moving relative to a wire connected in a complete circuit can cause a current to flow in the wire.
A magnet moving in the opposite direction relative to a wire induces a current in the opposite direction.
A magnet moving relative to a wire can cause a potential difference across the wire called the induced potential.
Induced potential is proportional to mag. field strength and the relative speed of movement between a wire and a magnet.
For a magnet moving relative to a coil, the induced potential is proportional to the number of turns of wire in a coil.

Keywords

Induced current - The current generated in a circuit moving relative to a magnetic field.
Generator effect - The effect of inducing a current by the relative movement of a circuit and a magnetic field.
Milliammeter - A sensitive ammeter able to measure thousandths of an amp.
Induced potential - The potential difference generated in a conductor moving relative to a magnetic field.

Common misconception

Magnets can attract or repel electric charges in a wire.

Explain that the cause of induced current is complex and is usually taught to students studying physics at university. At this point it is sufficient to be able to describe and predict what happens when a conductor is moving in a magnetic field.

It is not possible for (almost all) pupils to understand the cause and effect of this phenomenon at this stage of learning and it is important to make this clear to the class, because it is common for pupils to assume they are not good at physics if they cannot understand a clear cause and effect.

Teacher tip

Equipment

Demonstrate equipment to show induced potential or current on sensitive meters when moving magnets relative to coils of wire and/or wires relative to strong magnetic fields.

Licence

This content is © Oak National Academy Limited (2024), licensed on Open Government Licence version 3.0 except where otherwise stated. See Oak's terms & conditions (Collection 2).

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Worksheet

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Starter quiz

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6 Questions

Q1.

Which of the following is a definition of current?

The amount of charge between two points.

The time taken for a unit of charge to flow past a point.

Correct answer: The amount of charge flowing past a point every second.

Q2.

Which of the following is the name of an instrument used to measure current?

Correct answer: ammeter

ampmeter

voltmeter

voltagemeter

Q3.

Which of the following is used to measure potential difference?

potometer

potentiometer

Correct answer: voltmeter

voltagemeter

Q4.

There is a potential difference between two ends of a wire. Which of the following statements are correct?

There must be a current in the wire.

Correct answer: There is an electric field between the ends of the wire.

Correct answer: A voltmeter connected across the ends of the wire would show a non–zero reading.

Q5.

Which of the following describes the motor effect?

Correct answer: A force acts on a current–carrying wire in a magnetic field.

A force acts on a current–carrying wire in an electric field.

A current–carrying wire exerts a force on a magnetic field.

A current-carrying wire exerts a force on an electric field.

Q6.

Which of the following statements about batteries are correct?

Correct answer: A battery can supply energy to a circuit.

Correct answer: The ends of a battery are called terminals.

Correct answer: A battery has one positive end and one negative end.

A battery has no potential difference between its ends.

Exit quiz

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6 Questions

Q1.

Which of the following is used to measure very small currents?

megameter

miniammeter

Correct answer: milliammeter

multiammeter

Q2.

Which of the following describes the generator effect?

Correct answer: A current appears when a circuit and magnetic field move relative to each other.

A magnetic field appears when a current and circuit move relative to each other.

A circuit appears when a magnetic field and current move relative to each other.

Q3.

The diagram shows a piece of wire in a magnetic field, represented by field lines. In which directions can the wire be moved to make a current appear in the wire?

to the left (along the wire’s length)

to the right (along the wire’s length)

Correct answer: upwards

Correct answer: downwards

Q4.

When current appears in a wire because the wire is pushed through a magnetic field, this is called current.

Correct Answer: induced

Q5.

A pupil has a coil which is part of a complete circuit, and also a magnet. Which of the following are ways of making a current appear in the coil?

Leave the magnet in the middle of the coil.

Correct answer: Move the magnet into the coil.

Correct answer: Move the magnet out of the coil.

Correct answer: Hold the magnet still and move the coil so that the magnet goes inside it.

With the magnet in the coil, move both at the same speed in the same direction.

Q6.

A magnet is moved into a stationary coil, causing a current in the coil. Which of the following statements are correct?

Correct answer: There is an induced potential across the coil.

Correct answer: Moving the magnet out of the coil changes the current direction.

While the magnet moves into the coil, there is a force pushing it sideways.

Correct answer: If the magnet moves twice as fast, the current doubles.

If the number of turns of the coil is doubled, the current halves.