Magnetism

Properties of Magnets zAll magnets have two areas of strongest force, called poles. zEach magnet has one north pole and one south pole. zLike poles repel, and opposite poles attract. zThe magnetic region where you can “feel the force” is called a magnetic field.

Magnetic Materials zWhat makes some things magnetic, while other things can’t be magnetized? zSpinning electrons cause small magnetic fields around each atom. zMagnetic materials have atoms whose magnetic fields can be lined up in the same direction. zAreas where atoms’ magnetic fields line up are called magnetic domains. magnetic domain z Randomly arranged domains = No magnet! z Magnetic domains lined up = Magnet!

The Earth is a magnet! magnetic north pole geographic north pole magnetic south pole geographic south pole z Magnetic lines of force around the earth are like the field lines around a giant bar magnet. z The magnetic north pole and the geographic north pole are not located in the same place! z The north pole of a compass points to the earth’s magnetic north pole.

Electricity to Magnetism zIn 1820, H.C. Oersted discovered that an electric current flowing through a wire had a magnetic field around it. zElectricity can cause magnetism! zElectromagnets are powerful magnets that can be turned on and off. z You can make an electromagnet stronger by (1) putting more turns of wire in the coil or (2) making a larger soft iron core, or (3) increasing the current through the wire.

Uses for electromagnets zA simple DC electric motor contains a permanent magnet, an electromagnet, and a commutator. When current flows through the electromagnet, it turns within the magnetic field of the permanent magnet, changing electricity to mechanical energy. z Current meters also use permanent magnets and electromagnets. When current flows through a wire, it makes an electromagnet. The force between the electromagnet and the permanent magnet makes a needle move on the meter.

Magnetism to Electricity zJoseph Henry and Michael Faraday discovered that magnetism could also produce electric current. This is called electromagnetic induction. z If a magnet is moved back and forth through a coil of wire, current can be made to flow through the wire. This is the idea behind electric generators and transformers. Current moves left in wire. Current moves right in wire.

Uses for Electromagnetic Induction zGenerators produce AC current for home and industrial use. Water, wind, or steam are used to move large electromagnets through the coils of wire to produce current. z Transformers are used to step up voltage of electricity that must travel long distances through wires. Other transformers then step down the voltage before it enters our homes.