A security system uses a microphone to detect sounds in a building. The microphone produces an oscillating current that is sent to a monitoring device. Describe what is meant by an oscillating current and explain why the current produced by the microphone oscillates.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (4 marks)
An oscillating current is one that repeatedly changes direction and magnitude over time.
The sound waves in the building make the microphone diaphragm vibrate.
The diaphragm is attached to a coil that moves back and forth inside a magnetic field.
As the coil cuts through the magnetic field its motion induces a voltage that changes sign each time the coil reverses, so the current alternates – it is oscillating.
The sound waves in the building make the microphone diaphragm vibrate.
The diaphragm is attached to a coil that moves back and forth inside a magnetic field.
As the coil cuts through the magnetic field its motion induces a voltage that changes sign each time the coil reverses, so the current alternates – it is oscillating.
Examiner tips
- Use the term "oscillating current" to show understanding of the definition.
- Explain the chain: sound → diaphragm vibration → coil motion → magnetic induction → alternating current.
- Show the direction change explicitly – the current reverses each time the coil moves.
- Keep the answer concise – 4 marks, so one sentence per point is enough.
Common mistakes
- Confusing oscillating current with a DC current – forgetting the direction change.
- Not linking the diaphragm vibration to the coil movement in a magnetic field.
- Using vague terms like "changing current" without specifying alternation.
Mark scheme (4 marks)
- An oscillating current is one that repeatedly changes direction (alternates) / varies in size and direction over time
- Sound waves cause the diaphragm of the microphone to vibrate
- The vibrating diaphragm causes a coil (attached to it) to move back and forth inside a magnetic field
- The coil cutting through the magnetic field induces a current / voltage that changes direction as the coil reverses, producing an oscillating current
Key terms in this question
Related
- All Eduqas GCSE Physics revision notes →
- How to answer a "Describe and Explain" question →
- Decode the mark scheme abbreviations →
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