ME6 - Electric motors and loud speakers

Question 1

What four factors will speed up an DC electric motor?

Answer 1

• More current
• More turns on the coil
• Stronger magnetic field
• A soft iron core in the coil

Question 2

How can a simple electric motor be built?

Answer 2

Using a coil of wire that is free to rotate between two opposite magnetic poles. When an electric current flows through the coil, the coil experiences a force and moves (interaction)

Question 3

Describe how an electric motor works

Answer 3

A force is acting on the two side arms of the coil. Because the coil is on a spindle (one side acts up and the other down) it rotates

(it is the forces between the two magnetic fields that cause the coil to turn, transferring electrical energy to kinetic energy)

Question 4

What is used to make sure when the coil rotates, it doesn’t get stuck?

Answer 4

Split- ring commutator - clever why of swapping the contacts every half turn to keep the motor rotating in the same direction

Question 5

How can the direction of the motor be reverses?

Answer 5

• Swap the polarity of the dc supply

- Swap the magnetic poles over

Question 6

What can be used to work out which way the current will turn?

Answer 6

Flemings left hand rule

Question 7

What works because of the motor effect?

Answer 7

Loudspeakers

Question 8

How does the loudspeaker work?

Answer 8

AC electrical signals from an amplifier are fed to a coil of wire in the speaker which is wrapped around the base of the cone

Question 9

What is the coil in the loudspeaker surrounded by?

Answer 9

A permanent magnet - the ac signals cause a force on the coil and make it move back and forth

Question 10

What do the movements of the coil produces?

Answer 10

The cones vibrate which creates sounds