Explain how the generator effect produces AC in alternators and DC in dynamos, and draw or interpret graphs of generated potential difference against time.
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GCSE Physics Revision
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GCSE Physics revision
Uses of the generator effect (HT only)
Induced potential, transformers and the National Grid (physics only) (HT only)
Your specification
AQA student objectives
Learning pathway
All · Most · Some
Apply the scientific explanation of uses of the generator effect to a relevant example.
Analyse a new situation involving uses of the generator effect and explain the scientific reasoning.
Revision summary
Key knowledge
Read on screen, then print for Cornell-style active revision.
What is the Generator Effect?
- The generator effect, also known as electromagnetic induction, is the process by which a potential difference is induced in a wire when it experiences a change in magnetic field.
- A coil of wire moved through a magnetic field between two magnets will have a potential difference induced across it, shown by the presence of positive and negative terminals.
- It is the change in the magnetic field experienced by the wire that is the key condition — without movement, there is no change and therefore no induced potential difference.
Direction of the Induced Potential Difference
- The direction of the induced potential difference reverses each time the direction of movement is reversed, causing the polarity (plus and minus) to switch.
- Moving the magnets instead of the wire produces the same effect, as the wire still experiences a change in magnetic field.
- Moving the wire parallel to the field (back and forth without cutting through field lines) does not induce a potential difference, as the wire experiences no change in magnetic field.
From Potential Difference to Current
- An induced potential difference alone cannot drive a current unless the wire forms a complete (closed) circuit.
- When the two ends of the wire are connected to complete the circuit, the induced potential difference causes electrons to flow, generating an induced current.
Factors Affecting the Size of the Induced Potential Difference
- Increasing the strength of the magnetic field (e.g. using stronger magnets) increases the size of the induced potential difference.
- Increasing the speed at which the wire or magnets move causes the magnetic field to change more rapidly, resulting in a larger induced potential difference.
- Increasing the number of turns on the coil increases the induced potential difference, as more wire is cutting through the magnetic field lines.
Moving a Magnet Into and Out of a Coil
- Moving a single magnet into and out of a coil of wire induces a potential difference in the coil due to the changing magnetic field experienced by the coil.
- When the circuit is complete, this induced potential difference drives a current around the circuit.
- Reversing the direction of the magnet's movement reverses the direction of the induced current.
- Swapping the poles of the magnet (e.g. turning it around) also reverses the direction of the induced current.