Induced Potential and the Generator Effect
Learn Induced Potential and the Generator Effect for GCSE Physics with this free worksheet and full mark scheme — Higher-tier exam-style questions with worked answers for AQA, Edexcel and OCR. A separate (triple) physics topic: a changing magnetic field induces a potential difference in a conductor, and this can be increased by moving faster or using a stronger field.
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These worksheets and mark schemes are original, written for Virtus Academy and checked against the current AQA, Edexcel and OCR specifications. Every worksheet comes with a full mark scheme.
This is a Higher tier only topic, so there's no Foundation paper — only the Higher worksheet and mark scheme below.
Topic overview
If an electrical conductor moves relative to a magnetic field, or if the magnetic field through a coil changes, a potential difference is induced across the ends of the conductor. This is the generator effect. This is a Triple-only and Higher-only topic.
If the conductor is part of a complete circuit, a current is induced as well as a potential difference.
An induced current always creates a magnetic field that opposes the original change. This means the effect always acts to resist whatever caused it — pushing a magnet into a coil produces a force opposing the push. The size of the induced potential difference increases with faster movement, a stronger field, or more turns on the coil.
Revision notes
The generator effect
Moving a conductor relative to a magnetic field, or changing the field through a coil, induces a potential difference across the ends of the conductor.
If the conductor forms part of a complete circuit, a current is induced as well.
Opposing the change
The induced current generates a magnetic field that opposes the original change.
So pushing a magnet into a coil produces a force opposing the push, and pulling it out produces a force opposing the pull. The effect always resists what caused it.
Increasing the induced potential difference
Move the conductor or magnet faster. Use a stronger magnetic field.
Increase the number of turns on the coil. Each increases the rate at which the field through the coil changes, which is what determines the size of the induced potential difference.
Key points
- Movement or a changing field induces a potential difference.
- A complete circuit also gives an induced current.
- The induced current opposes the original change.
- Faster movement gives a larger induced potential difference.
- A stronger field gives a larger induced potential difference.
- More turns give a larger induced potential difference.
Worked examples
Example 1
State three ways to increase the potential difference induced in a coil. [3 marks]
Model answer
Move the magnet or coil faster (1 mark). Use a stronger magnetic field (1 mark). Increase the number of turns on the coil (1 mark).
Example 2
Explain why a force is felt when pushing a magnet into a coil. [3 marks]
Model answer
Moving the magnet induces a current in the coil (1 mark). The induced current creates its own magnetic field (1 mark), which opposes the change causing it, so a force is felt opposing the push (1 mark).
Example 3
Explain the difference between an induced potential difference and an induced current. [2 marks]
Model answer
A potential difference is induced whenever there is relative movement or a changing field (1 mark), but a current only flows if the conductor forms part of a complete circuit (1 mark).
Common mistakes
Saying a current is always induced.
A potential difference is always induced; a current requires a complete circuit.
Saying the induced field assists the change.
It always opposes the change that caused it.
Forgetting relative movement.
Either the conductor or the magnet can move — what matters is the relative motion.
Giving only one way to increase the induced potential difference.
Speed, field strength and number of turns are all examinable.
Exam tips
- Distinguish induced potential difference from induced current.
- Always state that the induced effect opposes the change.
- Give all three ways to increase the effect.
- Remember this is Triple-only AND Higher-only.
Key terms
- Generator effect
- Inducing a potential difference by relative movement or a changing field.
- Induced current
- Current flowing when the conductor is in a complete circuit.
- Opposing the change
- The principle that induced effects resist their cause.
- Relative movement
- Movement of the conductor or the magnet with respect to the other.
Related topics
Written and reviewed against the current AQA, Edexcel and OCR specifications. Spotted an error? Let us know.