7.2.3-4 - Electric Motors & Loudspeakers

How does an electric motor work?

• A coil of wire, carrying a current, is placed in a magnetic field.

• The forces on the two sides perpendicular to the field experience forces in opposite directions.

• This causes a rotational effect.

How do loudspeakers make use of the motor effect?

The motor effect is used to convert variations in the current of an electrical circuit into the pressure variations which produce audible sound.

Explain how a loudspeaker works.

• A cone with a wire wrapped around it is connected to an a.c power supply and is placed in a permanent magnetic field.

• When current flows through the wire, it creates a second magnetic field, which interacts with the permanent field.

• This produces a force which causes the cone to vibrate.

How is the pitch of the sound from a loudspeaker changed?

• The frequency of the a.c current is altered.

• This creates a different frequency of vibration of the cone.