O-LevelPhysicsMagnetism5054/22 · May/June 2016 · Q85 Marks

A transformer and a diode are used to charge a battery. Fig. 8.1 shows the transformer, which contains a soft-iron core and two coils. The primary coil is connected to the 240V a.c. mains supply. The secondary coil is connected in series with the diode and the battery.

(a)Explain why an electromotive force (e.m.f.) is induced in the secondary coil.[2]
(b)The e.m.f. induced in the secondary coil is less than 240V. Suggest why.[1]
(c)Suggest why steel is not used as the core of a transformer.[1]
(d)Describe the action of the diode.[1]

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Mark scheme

Marking points from the official mark scheme (May/June 2016). The mark or mark type is shown in brackets.

[1] current/a.c (in primary coil) creates magnetic field or current/a.c magnetises iron
[1] changing magnetic field (in secondary)
[1] it/secondary has less turns (than primary) or primary has more turns (than secondary) or (some) flux escapes
[1] (steel is) a permanent magnet or weaker fields produced or (steel) difficult to magnetise/demagnetise or (steel) is a hard magnetic material
[1] passes current/charge in one direction or has high resistance/is an insulator when current in one direction/reverse biased

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