Electromagnetism
4 marks · EasyA coil of wire is connected to a sensitive ammeter as shown. A bar magnet is moved into and out of the coil.
State what effect moving the magnet into the coil has on the ammeter reading.
Explain why a current is induced in the coil when the magnet is moved.
State two changes you could make to increase the size of the induced current.
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.
Show answer
(a) When the magnet is moved into the coil, the ammeter shows a current.
(b) A current is induced because moving the magnet into the coil causes a change in the magnetic field cutting the coil. This 'cuts' the magnetic field lines and induces a voltage (and so a current) in the coil.
(c) Move the magnet faster; use a stronger magnet; use a coil with more turns. (any two)
Common mistakes: Saying current is always present even when magnet is stationary
Show mark scheme and worked solution
Marking points
B1 (a) · 1 mark · States that a current appears on the ammeter when the magnet moves into the coil.
B2 (b) · 1 mark · Explains that moving the magnet causes a change in magnetic field in the coil.
B3 (b) · 1 mark · Correctly links magnetic field change to induced voltage and current.
B4 (c) · 1 mark · Names any two ways to increase the induced current: move faster, use a stronger magnet, or more turns in coil.
Worked solution
a) The ammeter shows a current when the magnet enters the coil.
b) Moving the magnet changes the magnetic field through the coil, so magnetic field lines are 'cut' by the coil. This induces a voltage and causes a current to flow if the circuit is closed.
c) To increase the induced current, move the magnet faster, use a stronger magnet, or use a coil with more turns.