Lesson 8

Electromagnet

We know that all magnets have two ends, usually marked "north" and“south,“And that magnets attract things made of steel or ironWe also know the fundamental law of all magnets: Opposites attract and likes repel.

An electromagnet works in the same way, except it is "temporary" the magnetic field only exists when electric current is flowing.

An Electromagnet

                               

You will find that this magnet is able to pick up small steel things like paper clips, staples and tacks.

Simple electromagnet

doorbell-chime.url

The Coil

circular magnetic field develops around the wire

LESSON

NOTES

We have learnt that electricity must flow in a circuit. In a battery, electricity flows from one terminal of the battery to the other. In a house, power flows from live to neutral. The appliance you plug into a socket completes the circuit from the live slot to the neutral slot, and electricity flows through the appliance.Let's say you plug a light bulb into the socket. The power will flow from the live prong, through the filament and back to the neutral prong, creating light in the process. The fuse prevents the wires in the wall or the outlet itself from overheating and starting a fire. The idea behind the earth wire is to protect the people who use metal-encased appliances from electric shock.

An Electromagnet

An electromagnet starts with a source of power and a wire.If you look at a battery, you can see that there are two ends,one marked plus (+) and the other marked minus (-).Electrons collect at the negative end of the battery, and,

if you let them, they will gladly flow to the positive end. The way you "let them" flow is with a wire. If you attach a wire directly between the positive and negative terminals

3 things will happen: 1.Electrons will flow from the negative side of the battery to the positive side as fast as they can. 2.The battery will drain fairly quickly (in a matter of several minutes). Normally, you connect some kind of load in the middle of the wire so the electrons can do useful work. The load might be a motor, a light bulb, a radio or whatever. 3.A small magnetic field is generated in the wire.It is this small magnetic field that is the basis of an electromagnet.

electromagnet.electromagnet is a coil of wire, often wrapped around a piece of magnetic metal. Electromagnets work on a very simple principle. Running electrical current through wire creates a very small magnetic field around the wire. Coiling the wire amplifies this magnetic field,so it has a substantial effect on any magnetic objects around it. Just like the magnetic field around a permanent magnet, the magnetic field of an electromagnet has a polar orientation -- a "north" end and and a "south" end -- and it is attracted to iron objects. When you hold down a doorbell button, it closes an electrical circuit so that household current flows through the electromagnet (or electromagnets) by way of a transformer. The transformer is a simple device that takes the 120-volt household current and steps it down to a 10-volt current This current is then passed through the electromagnet wire.