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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