O-LevelPhysicsMagnetism5054/21 · May/June 2022 · Q57 Marks

Fig. 5.1 shows a simple d.c. motor used in a toy car.[Figure 5.1]

(a)Terminals A and B are connected to a battery and the motor rotates. On Fig. 5.1, add labels inside the boxes to identify the parts of the motor indicated.[2]
(b)(i)State what happens to the rotation of the coil when: the number of turns on the coil is increased[1]
(b)(ii)the magnetic field between the poles of the magnet is reversed.[1]
(c)(i)The power supply to the motor is switched on and off at a steady rate. Fig. 5.2 shows how the speed of the toy car varies with time as a result of the power supply being switched on and off. Describe the motion of the toy car.[Figure 5.2][2]
(c)(ii)The voltage supplied to the motor is switched on for a longer period of time and off for a longer period of time, at a steady rate. Suggest what happens to the motion of the toy car.[1]

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Mark scheme

Marking points from the official mark scheme (May/June 2022). The mark or mark type is shown in brackets.

[1] (a) brush / carbon
[1] (a) split-ring or commutator
[1] (b)(i) faster or greater turning effect
[1] (b)(ii) goes backwards / turns backwards / reverses
[1] (c)(i) speeds up and slows down (when turned on/off)
[1] (c)(i) reaches a steady speed / terminal speed / maximum speed or slows down but never to rest or cycle continuously repeats
[1] (c)(ii) same top / constant speed or constant speed / maximum speed for a longer time or drops to a lower speed / comes to rest

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