When a current flows through a wire, a magnetic field is set up around the wire, made up of concentric circles as shown. The "right-hand rule" allows us to identify the direction of this magnetic field. If you look at the diagram you will understand that if you reverse the direction of current flow (that is the thumb points downwards) then the direction of the magnetic field will reverse.




There are a number of things to remember with magnetic fields:


  • The closer you are to the wire, the stronger the magnetic force will be, and conversely, as you move away from the wire the magnetic field/force felt will decrease.

  • The closer together the lines of force are, the stronger the magnetic field will be, so in the diagram of the straightforward "bar magnet" where the lines of force are shown closer together at the poles and this is where the magnetic force will be the strongest.



It is important to remember that the closer together the lines of force are, the stronger the magnetic field will be at that point. We will see a good application of this when we start to look at solenoids and electromagnets.