Magnets and Electromagnets

What are magnetic materials A magnetic material is attracted to a magnet. Only iron (Fe), nickel (Ni) and cobalt (Co) are magnetic materials.

The test for magnetism The test to see if a material is a magnet is through REPULSION. If another magnet is held close to it…it will attract when OPPOSITE poles are held close together but REPEL when the same poles are held close together S N

Magnetic Fields The region around a magnet where it has a magnetic effect is called its magnetic field. When a magnetic material is placed in a magnetic field it will experience a force. The iron filings feel the effect of the magnetic field and show the direction of the forces in this region.

Field Line Arrangement Field lines are shown by arrows and always move from North to South Field lines close together show a stronger magnetic force Field lines don’t cross N N S NN

Making a magnet A magnet can be made by magnetizing a material which is attracted to a magnet, e.g. a paper clip. There are three methods that can be used to make a magnet: Stroke a magnet along the paperclip from one end to the other and then starting from the same place, repeat the movement. The more times this is done, the more magnetic the clip becomes. Hold a nail in a magnetic field and hit it with a hammer. Put a magnetic material in a strong magnetic field.

Electromagnets When electricity is passed through a coil of wire, the coil has a magnetic field around it similar to a bar magnet. This type of electromagnet is called a Solenoid

How to make an electromagnet stronger…….. We can make an electromagnet stronger by doing these things: wrapping the coil around an iron core adding more turns to the coil increasing the current flowing through the coil.

Uses of Electromagnets A large electromagnet is used in a scrap yard to pick up and move heavy pieces of scrap metal. Questions: What metals would the electromagnet pick up? 2. What advantages does an electromagnet have over a permanent magnet?

The electric doorbell

How it works Electric bells like the ones used in most schools also contain an electromagnet. When the current flows through the circuit, the electromagnet makes a magnetic field. The electromagnet attracts the springy metal arm. The arm hits the gong, which makes a sound. The circuit is broken now the arm is out of position. The electromagnet is turned off and the springy metal arm moves back. The circuit is complete again.

Relay Switches Lifts, cars and other large electrical machines use high currents. A relay, which includes an electromagnet, is used to allow a small current in one circuit to control a large current in another circuit.