GENERATORS
4 marks · NormalA student builds a device by pushing a bar magnet in and out of a coil of wire connected to a voltmeter.
Explain why a voltage is seen on the voltmeter when the magnet moves.
State two changes the student can make to increase the maximum voltage produced.
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 because the magnet's movement causes magnetic field lines to be cut by the wire (or to cut through the coil), producing a voltage by electromagnetic induction.
(b) Move the magnet faster; use a stronger magnet; use a coil with more turns. (any two)
Common mistakes: Only saying 'a voltage is produced' for (a) without reference to movement or field lines
Show mark scheme and worked solution
Marking points
M1 (a) · 1 mark · Mentions that a voltage is induced (or current if circuit complete) when the magnet moves through the coil (or coil moves in magnetic field).
A1 (a) · 1 mark · States that this is because the field lines are cut by the wire (or wire cuts through magnetic field lines), not just contact.
B1 (b) · 1 mark · Gives one valid way to increase induced voltage (move magnet faster, use stronger magnet, or increase number of turns in the coil).
B2 (b) · 1 mark · Gives another valid but different way (as above).
Worked solution
a. A voltage is induced when the magnet moves because the movement means magnetic field lines are cut by the wire (or cut through the coil), causing electromagnetic induction. b. The size of the voltage can be increased by (any two): - moving the magnet more quickly - using a stronger magnet - increasing the number of turns in the coil.