What is the motor effect?

The effect in which a conductor carrying a current in a magnetic field and the magnet producing that field exert a force on each other.

A current-carrying wire between the poles of a magnet is pushed upwards. What force acts on the magnet?

An equal force acts on the magnet in the opposite direction, because the wire and the magnet exert a force on each other.

How must the thumb and the two fingers be held for Fleming's left-hand rule to work?

They must be held at right angles to one another.

AQA GCSE Combined Science Physics 8464

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Magnetism and Electromagnetism

Fleming's left-hand rule and electric motors

3 things to know
Physics Paper 2

Overview

The motor effect and the force on the magnet, Fleming's left-hand rule, the factors deciding the force on a conductor, the equation F = BIl with its units and calculations of force and magnetic flux density, and why a current-carrying coil turns in a simple electric motor that needs a split-ring commutator.

What you need to know

Answer each one before you reveal it.

Your recallNot started

Key term

Which hand is used for the rule that gives the relative directions of force, current and magnetic field for the motor effect?

Key term

In Fleming's left-hand rule, what does each of the first finger, the second finger and the thumb represent?

Key term

State the three factors that decide the size of the force on a current-carrying conductor in a magnetic field.

Questions from this subtopic

Each one with the model answer underneath.

1
What is the motor effect?
Model answer
The effect in which a conductor carrying a current in a magnetic field and the magnet producing that field exert a force on each other.
2
A current-carrying wire between the poles of a magnet is pushed upwards. What force acts on the magnet?
Model answer
An equal force acts on the magnet in the opposite direction, because the wire and the magnet exert a force on each other.
3
Which hand is used for the rule that gives the relative directions of force, current and magnetic field for the motor effect?
Model answer
The left hand.
4
In Fleming's left-hand rule, what does each of the first finger, the second finger and the thumb represent?
Model answer
The first finger is the direction of the magnetic field, the second finger is the direction of the current and the thumb is the direction of the force, or motion.
5
How must the thumb and the two fingers be held for Fleming's left-hand rule to work?
Model answer
They must be held at right angles to one another.
6
State the three factors that decide the size of the force on a current-carrying conductor in a magnetic field.
Model answer
The magnetic flux density of the field, the size of the current and the length of conductor that is in the field.

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