AQA · GCSE · Physics
Course version: 8463 · Version from Sept 2016
Induced potential (HT only): This is called the generator effect.
The name is worth learning precisely, because the two effects are mirror images and the examiner is watching which one you pick.
Checked against the AQA 8463 specification (opens in a new tab) on .
- Point 3 of 7
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
The name is worth learning precisely, because the two effects are mirror images and the examiner is watching which one you pick. The motor effect starts with a current and produces movement. The generator effect starts with movement, or with a changing field, and produces a potential difference. Anything that works one way round usually works the other: spin a motor by hand and it generates, and run a loudspeaker backwards and you have a microphone. Sort a question by what is supplied: supply a current in a field and a force is produced, which is the motor effect; supply movement or a changing field and a potential difference is induced, which is the generator effect. Quote the wrong effect and the rest of an otherwise correct answer usually earns nothing.
What earns the marks
- Naming the generator effect, where movement or a changing field produces a potential difference.
- Contrasting it with the motor effect, where a current in a field produces a force.
- Identifying a device that uses the generator effect, such as an alternator, a dynamo or a microphone.
- A potential difference being induced across the conductor, and a current only where the circuit is complete.
Common mistakes and how to put them right
Calling it the motor effect because a magnet and a coil are involved.
Saying the generator effect creates energy, rather than transferring it from the kinetic store of whatever turns the coil.
Naming the effect but never saying what is induced.
Pairing the left hand rule with a generator question.
Exam tips
- Ask what goes in: a current in means the motor effect, movement in means the generator effect.
- Learn one example of each effect, so that a one mark give an example question is free.
- Keep the word induced for the generator effect; it is the signal the examiner looks for.
Try the lesson
The start of the Induced potential (HT only): This is called the generator effect. lesson, made from checked teaching notes for this specification point.
Have a go first
A potential difference is induced across the ends of an electrical conductor when it moves relative to a magnetic field. What is the name of this phenomenon?
Listen
The name is worth learning precisely, because the two effects are mirror images and the examiner is watching which one you pick. The motor effect starts with a current and produces movement. The generator effect starts with movement, or with a changing field, and produces a potential difference. Anything that works one way round usually works the other: spin a motor by hand and it generates, and run a loudspeaker backwards and you have a microphone. Sort a question by what is supplied: supply a current in a field and a force is produced, which is the motor effect; supply movement or a changing field and a potential difference is induced, which is the generator effect. Quote the wrong effect and the rest of an otherwise correct answer usually earns nothing. A strong answer earns marks for these points. naming the generator effect, where movement or a changing field produces a potential difference. contrasting it with the motor effect, where a current in a field produces a force. identifying a device that uses the generator effect, such as an alternator, a dynamo or a microphone. a potential difference being induced across the conductor, and a current only where the circuit is complete. Exam tip: Ask what goes in: a current in means the motor effect, movement in means the generator effect.
See it
Key words
Say what each word means before you turn the card.
generator effect
Try answering aloud or in your head before turning the card.
motor effect
Try answering aloud or in your head before turning the card.
induced potential difference
Try answering aloud or in your head before turning the card.
energy transfer
Try answering aloud or in your head before turning the card.
See every definition
- generator effect
- Movement, or a changing field, produces a potential difference.
- motor effect
- A current in a field produces a force.
- induced potential difference
- A potential difference is induced across the conductor, and a current only where the circuit is complete.
- energy transfer
- Energy is transferred from the kinetic store of whatever turns the coil, rather than created.
Label the diagram
Some boxes have lost their names. Pick the right name for each number.
1Box 1
2Box 2
3Box 3
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