# Magnetism

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• Created by: holly6901
• Created on: 13-06-19 18:41

## Magnetism

• Magnets have a north pole (N) and south pole (S).
• If two magnets are close enough to each other, then the south pole of one magnet will attract the north pole of the other magnet.
• This is an example of a non-contact force.
• If one magnet is turned so that both south poles (or both north poles) are close together, then the magnets will repel each other.
• Opposite poles on a magnet attract and like poles on a magnet repel. This is an example of a non-contact force.
• A magnet's poles are where the magnetic forces are strongest.
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## Magnetic materials

• Magnetic materials, like iron, don’t always act as magnets.
• For example a normal piece of iron won’t attract (pull) or repel (push) another piece of iron.
• But magnetic materials, like iron, are attracted to a magnet if they are close enough to the magnet.
• Magnetic materials can be attracted by a magnet, but can’t be repelled by a magnet.
• Only two magnets can repel each other.
• Non-magnetic materials will never be attracted to magnets.
• Permanent magnets are always magnetic, even when they are not near other magnets.
• They produce their own magnetic field.

Magnetic materials

• Iron
• Nickel
• Cobalt
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## Induced magnetism

• Induced magnets are magnetic materials that become magnets when they are in a magnetic field.
• When moved away from the permanent magnet, the magnetic material will stop being a magnet.
• This is called induced magnetism.
• The permanent magnet induces (creates) temporary poles in the magnetic material and these align so that the magnetic material is attracted to the permanent magnet.
• If the north pole of the magnet is next to the magnetic material, then a south pole will be induced in the part of the material closest to the magnet.
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## Magnetic forces

Magnetic forces

• The strength of a magnetic field depends on the distance from the magnet. The magnetic field is strongest at the magnet’s poles.
• Every magnet creates a magnetic field around itself.
• A magnetic field is the area around a magnet where another magnet or magnetic material (iron, nickel, cobalt and steel) feels a force.

Magnetic field patterns

• A magnetic compass contains a small bar magnet. The needle of the compass points in the direction of the Earth’s magnetic field. This shows that the Earth’s core is magnetic.
• The arrows on magnetic field lines show the direction of a magnetic field. The arrows always point from the north pole of the magnet to the south pole.
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## Magnetic effect of a current

Magnetic effect of a current

• The magnetic field lines created by current are shown above in the image.
• The magnetic field lines are circles around a single conducting wire.
• The strength of the field depends on the size of the current and the distance away from the wire.
• The direction of the field lines depends on the direction of the current.
• Grip the wire with your right hand, with the thumb pointing in the direction of the current.
• Your fingers curled around the wire will point in the direction of the magnetic field.

Magnetic field of a solenoid

• The magnetic field is strong and uniform. This means that the magnetic field is of the same strength and in the same direction at every point.
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## Magnetic field of a solenoid

• Inside the coil of wire the field lines are evenly spaced, parallel, straight lines.
• Outside of the coil of wire, the field lines look like the field lines around a bar magnet, with a clear north and south pole (remember that magnetic field lines around a magnet go from North to South).
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## Magnetic field strength

• For a solenoid (coil of wire), the magnetic field inside the solenoid is strong and uniform.
• Outside of the solenoid the magnetic field decreases in strength the further away it is from the solenoid
• For a straight wire carrying a current, the magnetic field is strongest at the points closest to the wire, and weakest further away from the wire.
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