O-LevelPhysicsMagnetism5054/21 · May/June 2015 · Q75 Marks

A simple apparatus used to demonstrate electromagnetic induction is shown in Fig. 7.1. The coil is connected to two light-emitting diodes (LEDs). The magnet moves into and out of the coil. [Figure 7.1]

(a)Explain why there is an induced e.m.f. in the coil when the magnet moves.[2]
(b)Explain why one LED lights up when the magnet moves into the coil and the other LED lights up when the magnet moves out of the coil.[2]
(c)The LEDs are brighter when the magnet moves faster. Explain why.[1]

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Mark scheme

Marking points from the official mark scheme (May/June 2015). The mark or mark type is shown in brackets.

[1] field lines of magnet mentioned or magnetic flux mentioned
[1] field lines cut the coil or flux changes
[1] reversed movement of magnet causes one of
• reversal of (induced) emf
• reversal of (induced) current
• field lines cut/flux change in reverse direction
[1] LED emits light when current passes in one direction
[1] more current or more induced emf and flux lines cut faster or faster change in flux

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