Electromagnetic Induction
6 marks · NormalA small wind turbine uses a generator to produce electricity for charging batteries in a remote location. The generator works by spinning a coil inside a magnetic field.
State what is meant by electromagnetic induction in this context.
List two ways, other than increasing the strength of the magnets, that the voltage produced by the generator can be increased?
The voltage output from the generator is too low to charge the batteries efficiently. An engineer suggests using a transformer. The transformer has 60 turns on the primary coil and 240 turns on the secondary coil. The generator provides an input of 9 V a.c.
Explain why a transformer cannot be used if the generator produced direct current (d.c.) instead of alternating current (a.c.).
Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.
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(a) A voltage is induced when a conductor (the coil) cuts through magnetic field lines as it spins.
(b) Increase the speed of rotation; use more turns on the coil (accept: use a coil instead of a single wire).
(c) 36 V
(d) Transformers require a changing magnetic field, which only happens with a.c.; with d.c. the magnetic field is constant and no voltage is induced in the secondary coil.
Common mistakes: Mixing up increasing speed/number of turns with strength of magnet
Show mark scheme and worked solution
Marking points
B1 (a) · 1 mark · Correct description of electromagnetic induction in a generator context.
B1 (b) · 1 mark · Any correct way to increase induced voltage except 'stronger magnet'.
B2 (b) · 1 mark · Second correct way stated.
M1 (c) · 1 mark · Correct use of transformer equation: .
B1 (d) · 1 mark · States transformers need a changing magnetic field (or a.c.).
B2 (d) · 1 mark · Explains that with d.c. the field is not changing, so there is no induced voltage.
Worked solution
a) In a generator, electromagnetic induction is the process where a voltage is produced by spinning a coil (conductor) within a magnetic field, so the coil cuts through magnetic field lines.
b) Ways to increase the induced voltage are: - Spin the coil faster (increase speed of motion). - Use a coil with more turns of wire. (Either is correct; do not allow 'stronger magnet' since excluded.)
c) Use the transformer equation:
d) Transformers only work with alternating current (a.c.), because a.c. produces a changing magnetic field in the primary coil, which induces voltage in the secondary coil. With direct current (d.c.), the magnetic field does not change, so no voltage is induced in the secondary.