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Magnetism (Magnetism describes the ability of magnets to attract (pull…
Magnetism
Magnetism describes the ability of magnets to attract (pull towards) and repel (push away) other magnets without touching them.
Attraction:
- 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 no-contact force.
Repulsion:
- 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.
- Non-contact force.
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Magnetic Forces
- Magnetic forces (the forces between magnets) are caused by invisible magnetic fields.
Magnetic Fields:
- 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.
- When the magnetic fields of two magnets overlap, the fields cause the magnets to push or pull each other.
Strength of Magnetic Field:
- The strength of a magnetic field depends on the distance from the magnet. The magnetic field is strongest at the magnet's pole
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.
The Magnetic Effect of a Current:
- Any electric current produces a magnetic field.
Magnetic Field Lines:
- The magnetic field lines created by current are shown above in the image.
- The magnetic field lines are circles around a single conducting wire.
Strength of Magnetic Field:
- The strength of the field depends on the size of the current and the distance away from the wire.
Right Hand Grip
- The direction of the filed lines depend 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 around a Coil of Wire:
- A solenoid is a loop of wire coiled into a cylindrical shape.
Inside the coil:
- Inside the coil of wire the field lines are evenly spaced, parallel, straight lines.
Outside:
- Outside of the coil of wire the field lines look like the field lines around a bar magnet, with a clear north and south poles.
- REMEMBER: Magnetic field lines around a magnet go from North to South.
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Magnetic Materials:
Iron, Nickel and Cobalt are the only pure metals that can be turned into a magnet.
Properties of 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:
- 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.
- Permanent magnets produce their own magnetic field.
Induced Magnetism
A magnetic material will temporarily become a magnet when it is close to a permanent magnet. There is always an attractive force between an induced magnet (or magnetic material) and a permanent magnet.
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.
Poles:
- 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.