In: Physics
A magnetic field is a region in which a particle with magnetic properties experiences a force, and in which a moving charge experiences a force.
There are two main classes of magnet:
Permanent Magnets:
Permanent magnets are common and are made of iron, cobalt or nickel alloys.
To represent the field around a magnet we use a diagram which needs to obey some rules (or conventions) so that whoever uses it can interpret it correctly.
Here is an example:
The points to note are:
We draw lines to represent magnetic fields. These lines are called lines of flux.
The arrow shows the direction of the force that a free north pole, for instance a North pole with no South pole (which doesn't exist!) would feel.
Field direction always goes from North to South. So pop a magnet at X in the field (see diagram) and it would align itself with its North pole pointing along the arrow.
The spacing between the lines of flux tells you about the strength of field - as the lines get closer together, the field becomes stronger - for example, near the poles.
Look at this field:
The region in between the poles shows equally spaced, parallel lines. This is called a uniform field. Field strengthremains constant as you move around this area. Move out from the space between the poles and the field strength reduces. The lines of flux become further apart.
Temporary Magnets:
Around any conductor that has a current flowing through it there is a magnetic field. Switch off the current and the magnetic field disappears.