AQA · Physics · 8463
GCSE Physics: Uses of the generator effect
Magnetism and electromagnetism · AQA GCSE Physics (8463), specification point 4.7.3.2. Cards are generated from the exam board's own specification for "Uses of the generator effect", and every card links back to the page it came from. Higher tier only. Separate science only. Specification © AQA — used with attribution.
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What is the generator effect?
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A potential difference is induced across a conductor when it moves relative to a magnetic field (or when the field through it changes).
Which device uses the generator effect to produce alternating current (ac)?
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An alternator.
Which device uses the generator effect to produce direct current (dc)?
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A dynamo.
An alternator uses the generator effect to generate ?.
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ac
A dynamo uses the generator effect to generate ?.
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dc
Why does the coil of an alternator produce an alternating potential difference?
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As the coil rotates, each side moves up through the field then down, so the direction of the induced p.d. reverses every half turn.
What component in a dynamo makes the output dc rather than ac?
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A split-ring commutator — it swaps the coil's connections every half turn so the current always leaves in the same direction.
What component connects the rotating coil of an alternator to the external circuit?
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Slip rings (with brushes) — they keep each end of the coil permanently connected, so the output reverses as the coil turns.
What shape is the graph of potential difference against time for an alternator?
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A sine wave — the p.d. alternates smoothly between positive and negative values.
What shape is the graph of potential difference against time for a dynamo?
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A series of positive humps (a rectified sine wave) — the p.d. varies in size but never goes negative.
On a generator's p.d.–time graph, what happens to the peak p.d. if the coil spins faster?
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The peak p.d. increases (and the period decreases, so the peaks are closer together).
At which coil position is the induced p.d. in a generator zero?
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When the coil's plane is perpendicular to the field — its sides move parallel to the field lines and cut none.
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