8 Loud speakers, microphones and the national grid

Label the diagram

.

How do loud speakers work? - 7

1. a current in the coil creates a magnetic field

2. the magnetic field interacts with the permanent magnet generating a force, which pushes the cone outwards

3. the current is made to flow in the opposite direction

4. the direction of the magnetic field reverses

5. the force on the cone now pulls it back in

6. repeatedly alternating the current direction makes the cone vibrate in and out

7. the cone vibrations cause pressure variations in the air - which are sound waves

Label diagram

.

How does a microphone work?

1. pressure variations in sound waves cause the flexible diaphragm to vibrate.

2. the vibrations of the membrane cause vibrations in the coil

3. the coil moves relative to a permanent magnet, so a potential difference is induced in the coil

4. the changing size and direction of the induced current matches the vibrations of the coil

5. the coil is part of a complete circuit, so the induced potential difference causes a current to flow around the circuit

6. the electrical signals generated match the pressure variations in the sound waves

Label the national grid

.

Why are step down transformers used before the electricity reaches the house?

To make the PD going into homes safe.