Magnetism

  • 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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