Explain how an electromagnet works in a relay, including the role of the soft iron core and armature.

a) A suitable material for the core is soft iron.

b) When switch S is closed, current flows through the coil, which magnetizes the core. The core becomes an electromagnet.

c) When the core becomes an electromagnet, it attracts the soft iron armature. The armature pivots, causing contact B to move and touch contact A, thus closing the circuit for the motor.

When switch S is opened:

• The core: The current stops flowing, so the soft iron core loses its magnetism and becomes demagnetized.
• Soft iron armature: The core no longer attracts the armature. The springy metal strips pull the armature back to its original position, causing contacts A and B to open.