Electric Motors and Loudspeakers

Question 1

Name the 4 factors which speed up an electric motor

Answer 1

1) More current
2) More turns in the coil
3) A stronger magnetic field
4) Adding a soft iron core in the coil

Question 2

On the diagram [p62: cgp] what are the forces acting on

Answer 2

the 2 side arms of the coil

Question 3

What type of force is this

Answer 3

These are just the usual forces that act on any current in a magnetic field

Question 4

As the coil is on a spindle, what starts to happen

Answer 4

As it has one force up and one force down, it causes it to rotate

Question 5

What is the job of the split ring commutator

Answer 5

It swaps the contacts every half turn so that the motor rotates in the same direction

Question 6

How can you reverse the direction of the motor

Answer 6

By swapping the polarity of the d.c. supply or swapping the magnetic poles over

Question 7

What can we use to find out which way the coil will turn

Answer 7

Fleming’s left hand rule

Question 8

Where are the A.c. electric signals from the amplifier fed to in a loudspeaker?

Answer 8

They are fed to a coil of wire in the speaker which is wrapped around the base of a cone

Question 9

The coil is surronded by a permanent magnet, what is the purpose of this?

Answer 9

So that a.c. signals cause a force on the coil and make it move back and forth

Question 10

What do these movements in the loudspeaker cause?

Answer 10

They cause the cone to vibrate which creates a sound