The poles of a magnet
Magnetic pole
A magnetic pole is a place on a magnet where the magnetic forces are strongest.
- Every magnet has two poles: a north pole and a south pole.
- Two like poles repel, so a north pole pushes away another north pole, and a south pole pushes away another south pole.
- Two unlike poles attract, so a north pole and a south pole pull towards each other.
The rule to remember is: like poles repel; unlike poles attract.
Magnetic forces are non-contact forces
Non-contact force
A non-contact force is a force that acts between objects that are not touching.
- Attraction and repulsion between magnetic poles are examples of non-contact forces, because each magnet exerts a force on the other across a gap.
- The direction of the force depends on which poles face each other, so two north poles placed close together move apart because like poles repel.
Permanent magnets
Permanent magnet
A permanent magnet is a magnet that produces its own magnetic field.
- A permanent magnet can attract or repel another permanent magnet, depending on the poles that face each other.
- Like poles produce a repulsive force.
- Unlike poles produce an attractive force.
- A permanent magnet stays magnetic without being placed in another magnetic field.
Induced magnets
Induced magnet
An induced magnet is a material that becomes a magnet when it is placed in a magnetic field.
- When a magnetic material is placed near a permanent magnet, the permanent magnet's field makes it magnetic, and this is called induced magnetism.
- Induced magnetism always causes a force of attraction, so an induced magnet is attracted to the magnet that caused it and never repelled by it.
- When an induced magnet is removed from the field, it loses most or all of its magnetism quickly.
Question: A student moves the north pole of a permanent magnet close to an unmagnetised magnetic material. Describe what happens and explain how the material differs from the permanent magnet.
Answer: The material becomes an induced magnet because it is in the magnetic field of the permanent magnet. It is attracted to the permanent magnet, because induced magnetism always causes attraction. When it is removed from the field it loses most or all of its magnetism quickly, while the permanent magnet keeps producing its own magnetic field.
Comparing permanent and induced magnets
- A permanent magnet produces its own magnetic field and stays magnetic.
- An induced magnet becomes magnetic only while it is in a magnetic field.
- An induced magnet loses most or all of its magnetism quickly once removed from the field.
- Two permanent magnets can attract or repel, depending on the poles that face each other.
- Induced magnetism always causes attraction.
- Do not say every pair of magnets attracts, because two permanent magnets repel when like poles face each other.
- A permanent magnet and the induced magnet it produces always attract.
- Do not call magnetic attraction and repulsion contact forces, because they act across a gap and are non-contact forces.
- When comparing permanent and induced magnets, say what happens both inside and after leaving a magnetic field.
- For a pole question, state the pole relationship and the resulting force, for example: the north poles are like poles, so they repel.
- Where are the magnetic forces on a magnet strongest?
- What happens when two like poles are brought together?
- What happens when two unlike poles are brought together?
- Why are magnetic attraction and repulsion non-contact forces?
- What is the difference between a permanent magnet and an induced magnet?
- What happens to an induced magnet when it is removed from the magnetic field?
