2.3.3 Generating electricity Questions

1 What is the flux linkage if a square coil with 10 cm sides and having 500 turns interacts with a magnetic field, B = 0.33 mT?

2 The graph shown in fig. 2.3.19 is a trace of induced emf against time as a magnet is dropped through a coil of wire.

fig. 2.3.19

a Describe and explain the trace obtained.

b If the coil were connected in series to a light bulb, describe and explain how the current through the bulb would vary over time.

3 The coil from question 1 is turned through 90º within the 0.33 mT magnetic field, moving from a position perpendicular to the field, to a position parallel to the field. This action takes 12 ms. What is the induced emf in the coil? How would Lenz’s law cause the induced current to affect the movement?

4 A transformer for a toy train set converts the mains supply from 230 V down to 6 V to operate the model train. The transformer that makes this conversion has 160 turns on its secondary coil. How many primary turns does the transformer have?

2.3.3 Generating electricity Answers

1) 1.65 x 10-3 Wb-turns

2) a) The emf has a pulse in one direction, followed by a briefer, larger pulse in the opposite direction.b) The current moves in one direction, then drops to zero before a higher current moves in the opposite

direction.

3) 0.14 V The induced current causes a magnetic field which tends to try and stop the coil turning.

4) 6100 turns