ELECTRIC MOTORS AND ELECTROMAGNETIC INDUCTION
3 marks · NormalThe diagram shows a rectangular coil inside a simple electric motor. The coil rotates between the poles of a magnet.
State the purpose of the split ring in this motor.
Give two ways to increase the speed at which the motor turns.
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(a) The split ring reverses current direction in the coil every half-turn, allowing continuous rotation.
(b) Increase number of turns, increase current, increase strength of magnetic field. · must show Any two correct ways
Must show: Purpose stated, Two valid ways for speed increase
Also accept: Increase number of turns, increase current, increase field strength
Common mistakes: Not stating need for reversing current each half-turn
Show mark scheme and worked solution
Marking points
B1 (a) · 1 mark · Correctly states the split ring reverses current direction to keep the coil rotating.
B1 (b) · 2 marks · Gives two ways to increase turning speed, e.g., more turns, higher current, stronger magnet.
Worked solution
a) The split ring reverses the direction of current in the coil every half-turn so the coil keeps turning in the same direction.
b) Increase number of turns of the coil, raise current, increase magnetic field strength.