Induced Magnetism (Oxford AQA IGCSE Physics)
Revision Note
Induced Magnetism
An induced magnet is a material that becomes a magnet when it is placed in a magnetic field
Induced magnetism always causes a force of attraction
When removed from the magnetic field, the material will lose its induced magnetism quickly
Magnetic materials
Very few metals in the Periodic Table are magnetic
The magnetic metals are:
Iron
Cobalt
Nickel
Steel is an alloy which contains iron, so it is also magnetic
Magnetic materials
Magnetic materials (which are not magnets) will always be attracted to the magnet, regardless of which pole is held close to it
Magnets and magnetic materials
Bringing a material close to a known magnet will determine if the material is magnetic, non-magnetic or if it is a magnet itself
It is a magnet if it is repelled by the known magnet
It is a magnetic material if it is attracted to the known magnet
It is a non-magnetic material if it is neither attracted nor repelled by the known magnet
Types of magnets
There are two types of magnets
Permanent magnets
Induced magnets
Permanent magnets
Permanent magnets are made out of permanent magnetic materials (materials that are always magnetic), for example, steel
A permanent magnet will produce its own magnetic field
It will not lose its magnetism
Induced magnets
When a magnetic material is placed in a magnetic field, the material is temporarily turned into a magnet
This is called induced magnetism
When magnetism is induced in a material:
One end of the material will become a north pole
The other end will become a south pole
Magnetic materials will always be attracted to a permanent magnet
Induced magnetism
In the image above:
The north pole of the permanent magnet induces a south pole in the magnetic material (at the end closest to the magnet)
The south pole of the permanent magnet induces a north pole in the magnetic material (at the end clostest to the magnet)
Worked Example
The diagram below shows a magnet held close to a piece of metal suspended by a light cotton thread. The piece of metal is attracted towards the magnet.
Which of the following rows in the table gives the correct type of pole at X and the correct material of the suspended piece of metal?
Type of pole at X | Material of suspended piece of metal | |
|---|---|---|
A | North | Nickel |
B | South | Nickel |
C | North | Aluminium |
D | South | Aluminium |
Answer: A
X must be a north pole
The piece of metal is being attracted towards the magnet
The law of magnetism states that opposite poles attract
The material of the suspended piece of metal is nickel
Nickel is a magnetic material (it will experience a force when it is placed in a magnetic field, in this case, it is attracted towards the magnet)
B is incorrect because X cannot be a south pole (and hence is a north pole)
If the pole at X is a south pole then the piece of metal would be repelled from the magnet because the law of magnetism states that like poles repel
C and D are incorrect because aluminium is not a magnetic material
A non-magnetic material would be unaffected by the magnetic field produced by the magnet
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