O-LevelPhysicsMagnetism5054/21 · May/June 2023 · Q97 Marks

Fig. 9.1 shows a simple a.c. generator. [Figure 9.1]

(a)Explain why there is a voltage induced in the coil when the coil is turned.[2]
(b)In Fig. 9.1 the coil is horizontal, with side AB on the left. The output voltage is +6.0V. On Fig. 9.2 draw a line from each of the shaded boxes to one of the circled voltages to show the voltage output when the coil is in different positions. One line has been drawn for you. [Figure 9.2][2]
(c)(i)Fig. 9.1 shows how the brushes are connected to the coil in an a.c. generator. Draw a diagram to show how the brushes are connected to the coil in a d.c. motor.[2]
(c)(ii)State why there are forces on the sides of the coil in a d.c. motor.[1]

This question uses a diagram from the original paper, which isn't shown here. Open the full paper from the past papers archive to see it.

Mark scheme

Marking points from the official mark scheme (May/June 2023). The mark or mark type is shown in brackets.

[B1] magnetic field or magnetic flux mentioned (from magnets)
[B1] it/sides of coil cut (magnetic) field or (magnetic) field (strength) / flux in coil changes
[B1] AB on right -6V
[B1] coil vertical 0 V in both positions
[C1] one ring (instead of two) with gaps between the two halves
[A1] each side of split ring connected to a different end of the coil and to a brush
[B1] (force on) current in a magnetic field or left-hand rule mentioned or magnetic field of coil interacts with field of magnet

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