Electromagnets

Homework

Explain the use of electromagnets in four of the following (diagram aid):
a) Loudspeaker
b) Telephone
c) Electric Motor
d) Circuit Breaker
e) Relay Switch



A. Loudspeaker:

The loudspeakers in your radio, TV or stereo system use varying electric current through an electromagnet to create sound. The electric current varies at a fast rate, causing the strength of the magnetic field to vary. This results in moving the loudspeaker membrane or cone back and forth rapidly, resulting in sound and even music.

The coil of the electromagnet is called a field coil and is energized by direct current through a second pair of terminals. This winding usually served a dual role, acting also as a choke coil filtering the power supply of the amplifier which the loudspeaker was connected to.

Diagram:

B. Telephone:

Modern telephone systems rely on electromagnets. The telephone receiver is basically an electromagnet with a U-shaped yoke having coils wound on each leg of the U. Passage of the electrical signal through the coils causes magnetic attraction of a soft iron diaphragm supported a small distance from the ends of the U. The diaphragm moves in and out, pulling and pushes the air in front of it, generating sound waves. The pressure on the air sets up sound waves that are the same as the ones sent into the transmitter. The sound waves strike the ear of the listener and he hears the words of the speaker.


Diagram: Basic Electromagnet setup in telephones


C. Electric Motor:

An electric motor utilizes the property of electromagnetic induction to convert electricity into mechanical energy to make things move. Motors consist of two basic units, the field, which is the electromagnet with its coils, and the armature, the structure that supports the conductors. The conductor itself, a coiled wire, will move to oppose the magnetic field. Just when it gets into position the current is reversed, and the coil spins round and round like a dog chasing its tail, full of mechanical energy. The armature cuts the magnetic field and carries the exciting current to others parts of the motor to be used to do mechanical work.

Diagram:

D. Circuit Breaker:

In an electromagnet circuit breaker, the circuit breaker consists of a simple switch, connected to an electromagnet.

The hot wire in the circuit connects to the two ends of the switch. When the switch is flipped to the on position, electricity can flow from the bottom terminal, through the electromagnet, up to the moving contact, across to the stationary contact and out to the upper terminal.

The electricity magnetizes the electromagnet. Increasing current boosts the electromagnet's magnetic force, and decreasing current lowers the magnetism. When the current jumps to unsafe levels, the magnetic field in the electromagnet is strong enough to trip the breaker and allow the contacts to open. The entire linkage shifts, tilting the moving contact away from the stationary contact to break the circuit. The electricity shuts off.

Diagram: