4.7.3.3 Microphones (HT only)

Question 1

What do microphones use?

Answer 1

microphones use the generator effect to convert the pressure variations in sound waves into variations in current in electrical circuits

Question 2

How does a moving-coil microphone work?

Answer 2

• when sound waves hit the diaphragm they cause it to vibrate
• the diaphragm causes the coil/wire to vibrate
• the coil/wire moves through the magnetic field of permanent magnet and cuts the magnetic field lines
• this induces a p.d. across the ends of the coil/wire
• the p.d. switches direction as the coil moves backwards and forwards/changes direction through the magnetic field
• the frequency of the changing p.d. is the same as the frequency of the sound waves
• the changing pattern of p.d. is passed through an amplifier and then into a moving-coil loudspeaker - increases the volume of the sound

Question 3

Description of a moving-coil microphone:

Answer 3

• coil of wire attached to thin sheet of plastic (diaphragm)
• end of the coil of wire sits over permanent magnet

Question 4

Diagram of a moving coil-microphone:

Answer 4