Magnetism and Electricity

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Magnetic fields

Like Gravity,magnetism is a force that acts at a distance. Unlike gravity,magnetic forces can repel as well as attract.

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Repulsion and attraction

If you put two magnets close to each other,and two like poles  (North-North or South-South) are facing each other they will repel (this means push away).If two unlike poles (north-south) are together they will attract.

A magnet will attract a peice of magnetic material, but only two magnets can repel each other

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The Earth's magnetic field

The Earth has a magnetic field - in fact it behaves as if it has a giant bar magnet in its centre.

The north seeking pole of a magnet inside a plotting compass will point to magnetic north,which is not quite the same posistion as the geographic north pole.

(http://tse1.mm.bing.net/th?&id=OIP.M9ffd5c3a6091cc7ddc53326413b63409o0&w=300&h=250&c=0&pid=1.9&rs=0&p=0)

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Electro magnets

Whenever a current flows in a wire it creates a magnetic field around it.

this magnetic field can be used to magnetise an iron core - which will remain a magnet for as long as the current is flowing in the circuit.This gives us a magnet we can switch on and off,called an electro magnet.

The nail acts as an iron core inside the coil of wire - this makes the magnetic field stronger than if it was just the field around the wire itself.

You can also make the magnetic field stronger by having more turns on the coil or by having a larger current.

Electro magnets differ from ordinary magnets because the magnet can be turned on and off by switching the current on and off.

(http://www.electronics-tutorials.ws/electromagnetism/mag33.gif)

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Question Time

Q1) What two things can you change to make an electro magnet stronger?

A1) Having more turns on the coil wire

A2) Or by having a larger current

Q2) What is the advantage of an electro magnet compared to an ordinary magnet?

A) An electro magnet produces more current because it is controlled by electricity and can be switched on or off.

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