CAIE IGCSE Physics 4.5.3.3 Magnetic Effect of a Current Is Used Questions

Learn how relay coils become electromagnets to control a separate circuit safely.

Exam points

explain how current in a relay coil magnetises a soft-iron core or armature
describe how magnetic attraction operates and releases relay contacts or a bell mechanism
state why relays allow a low-power circuit to control a separate high-current circuit

[Maximum number: 3]

The electric starter motor in a car is switched on and off using a relay.
The relay consists of a plastic case and two flexible springy strips, X and Y, which are made of soft iron. These iron strips act as the switch when a circuit is connected between the terminals W and Z.

$Fig. 7.1 shows \(\mathrm{X$

Fig. 7.1 shows \(\mathrm{X

Fig. 7.2 shows the equipment from Fig. 7.1 inside a magnetising coil. The magnetising coil is in series with the 12 V car battery and switch S , which is open.

Switch S is now closed.

Explain what happens to the springy iron strips X and Y .

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CAIE IGCSE Physics 4.5.3.3 Magnetic Effect of a Current Is Used Questions question 1