Induced potential (HT only) — AQA GCSE Physics
Test yourself on Induced potential (HT only) with AQA GCSE practice questions.
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Induced potential (HT only) explained
There are two ways to get a potential difference for nothing: move a conductor across a magnetic field, or hold the conductor still and change the field around it.
Read the full explanation
Both amount to the same thing, the conductor cutting magnetic field lines. Push a wire down between the poles of a magnet and a potential difference appears across its ends; hold it still and the reading drops to zero, because nothing is being cut. Move the wire along the field lines rather than across them and again nothing is induced. A coil carrying an alternating current does the second job with nothing moving at all: its field grows, collapses and reverses, and any conductor sitting in that changing field has a potential difference induced across it. The word induced matters, because nothing is connected to the conductor.
Your focus
- Describe two different arrangements that induce a potential difference in a conductor.
- Explain why a wire moved along the field lines induces nothing, using the idea of cutting field lines.
- Predict the reading on a voltmeter connected to a wire held stationary in a steady magnetic field.
Induced potential (HT only) exam tips
Marking Points
- one mark for the conductor and the magnetic field moving relative to one another, or for the field around the conductor changing
- one mark for the conductor cutting magnetic field lines
- one mark for a potential difference being induced across the ends of the conductor
- one mark for stating that with no relative movement and no change of field, nothing is induced
Examiner Tips
- 💡Look for the word change; if nothing about the field or the position changes, nothing is induced.
- 💡State clearly which is moving, the conductor or the magnet, because only the relative motion matters.
- 💡Use the phrase a potential difference is induced across the ends, which is the wording the mark scheme prints.
Common Mistakes
- saying a current is induced when the circuit is open, since only a potential difference appears until the circuit is complete
- moving the wire along the field lines and still expecting a reading, when no field lines are being cut
- describing a steady magnetic field near a stationary coil as inducing a potential difference
- writing that the magnet gives the wire charge, rather than that a potential difference is induced