GCSE-readyGenerators, dynamos, microphones and loudspeakers
Moving a wire in a magnetic field induces a potential difference. Generators and microphones use this; loudspeakers use the motor effect to do the reverse.
Inducing a current
The induced current produces its own magnetic field that opposes the change that caused it. For example, pushing a magnet into a coil induces a current whose field repels the magnet.
A bigger p.d. comes from moving faster, using a stronger magnet, or using more turns on the coil.
In power stations, huge generators do this on a large scale.
Alternators and dynamos
Dynamo (d.c. generator): uses a split-ring commutator, which swaps the connections every half turn, so the output is direct current (it varies but is always in one direction).
Turning faster gives a higher peak p.d. and a higher frequency (for an alternator).
Microphones and loudspeakers
Loudspeaker: an alternating current flows in a coil inside a magnetic field. The motor effect produces a force that keeps changing direction, so the coil and the attached cone vibrate, making sound waves.
Explain how a microphone turns sound into an electrical signal.
- Sound waves make the diaphragm vibrate.
- The coil attached to it moves in the magnetic field.
- This induces an alternating p.d. with the same pattern as the sound.
Answer: Sound vibrates the diaphragm and coil in a magnetic field, inducing a p.d. that copies the sound wave.
Relative movement between a conductor and a magnetic field induces a p.d.; the induced current's field opposes the change. Alternators use slip rings (a.c.); dynamos use a split-ring commutator (d.c.). Microphones use induction; loudspeakers use the motor effect.
- Magnetic field
- The region around a magnet or current-carrying wire where a magnetic material or another magnet feels a force.
- Potential difference
- The energy transferred per unit charge between two points: E = Q × V. Unit volt (V). The International GCSE often calls it voltage.
- Current
- The rate of flow of charge. Unit ampere (A).
- Power
- The rate of energy transfer, or work done per second. Unit watt (W).
- Generator
- A device that uses electromagnetic induction to transfer energy from a kinetic store to an electrical supply.
- Frequency
- The number of waves passing a point each second. Unit hertz (Hz). f = 1 ÷ T.
All GCSE and International GCSE Physics key terms and definitions →
Try two quick questions
See if it has sunk in. Answers are marked straight away.
2 more questions
Try each one, then tap to check.
What part of a dynamo makes its output direct current?
- A split-ring commutator
- A fuse
- Slip rings
- A thermistor
Show the answer
Answer: A split-ring commutator
The commutator reverses the connections every half turn.
Why does a dynamo use a split-ring commutator?
- To reverse the connections each half turn so the current flows one way
- To slow the coil down
- To increase the voltage
- To make the current alternate
Show the answer
Answer: To reverse the connections each half turn so the current flows one way
The commutator keeps the output in one direction.
Check you have got it
Answer 6 quick questions with instant marking. If you get one wrong, GCSE-ready shows you why and gives you another go. It is free, and you do not need an account.
- Pearson Edexcel GCSE Physics (1PH0) specification, topic 13.1, 13.2, 13.3, 13.4 (Physics only)
- Pearson Edexcel International GCSE Physics (4PH1) specification, topic 6.12, 6.15, 6.16
Checked by the GCSE-ready editorial team, 17 October 2026. Last updated 2 October 2026. Spotted a mistake? Tell us and we will fix it.
What do exam command words like explain and evaluate mean? →