GENERATORS
3 marks · NormalA generator in a power station uses coils of wire and a rotating magnet. Explain how this generator produces electricity. State TWO factors that affect the size of the voltage it produces.
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The rotating magnet causes its magnetic field to rotate inside the wire coils, causing magnetic field lines to be cut by the wires, which induces a voltage. The voltage size depends on (i) how fast the magnet rotates, and (ii) the strength of the magnet (or number of coil turns).
Common mistakes: Not mentioning field lines are cut; Not giving two factors
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Marking points
M1 · 1 mark · Describes that rotation causes field lines to be cut by coil (or coil to cut field lines), inducing voltage.
B1 · 1 mark · States one valid factor affecting size of voltage (speed of rotation / speed of field cutting, strength of field, or coil turns).
B2 · 1 mark · States another valid factor.
Worked solution
The rotating magnet produces a changing magnetic field in the coil. As the magnet turns, the field lines sweep across the wire, and the coil cuts more field lines, which induces a voltage (and current if circuit is complete). Two factors: faster magnet rotation increases voltage, and using a stronger magnet also increases voltage.