magnetism

Question 1

explain how a moving coil microphone works

Answer 1

• sound waves cause the diaphragm to vibrate
• diaphragm causes coil to vibrate
• coil cuts magnetic field lines
• a potential difference is induced across the ends of the coil

Question 2

explain why when there is a current in the coil, the coil rotates continuously in an electric motor

Answer 2

• the sides of the coil experience a force in opposite directions
• the forces cause moments that act in the same direction
• the moments cause the coil to rotate
• each half-revolution the two halves of the commutator swap from one brush to the other
• so the commutator reverses the current
• keeping forces in the same direction

Question 3

The input pd causes an alternating current.
Explain why there is an alternating current in the output when the transformer is
connected to a circuit.

Answer 3

• ac causes a changing magnetic field around primary coil
• creates a magnetic field that changes direction in the core
• this induces an alternating pd across the secondary coil