Magnetic poles
- The poles of a magnet are the places where the magnetic forces are strongest.
- When two magnets are brought close together they exert a force on each other: like poles repel and unlike poles attract.
- Attraction and repulsion between two magnetic poles are examples of non-contact forces.
Permanent and induced magnets
- A permanent magnet produces its own magnetic field.
- 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 field, an induced magnet loses most or all of its magnetism quickly.
- Iron, steel, cobalt and nickel are magnetic materials.
Magnetic fields
- The magnetic field is the region around a magnet where a force acts on another magnet or on a magnetic material.
- The field is strongest at the poles and gets weaker further from the magnet.
- The direction of the field at any point is the direction of the force on a north pole placed there. Field lines go from the north (seeking) pole to the south (seeking) pole.
- The closer together the field lines, the stronger the field.
Compasses and the Earth
- A magnetic compass contains a small bar magnet that lines up with the magnetic field.
- A plotting compass can be used to plot the field lines around a magnet: move it around the magnet and mark the direction the needle points.
- The Earth has a magnetic field. A compass needle points north because it lines up with the Earth's field, which is evidence that the Earth's core is magnetic.
Key terms
- Magnetic pole
- A place on a magnet where the magnetic forces are strongest.
- Permanent magnet
- A magnet that produces its own magnetic field all the time.
- Induced magnet
- A material that becomes a magnet only when it is in a magnetic field.
- Magnetic field
- The region around a magnet where a force acts on magnets or magnetic materials.
- Magnetic material
- A material attracted by a magnet: iron, steel, cobalt or nickel.
- Field line
- A line showing the direction of a magnetic field, from north to south.
- Plotting compass
- A small compass used to find the direction of a magnetic field.