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Electromagnetism

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When a current flows through a conductor a magnetic field is produced in the vicinity of the conductor. The magnetic field is invisible but its presence can be detected using a compass needle (which will deflect from its normal north-south position).

A magnetic field will be set up in the space surrounding a conductor that is carrying an electric current. The magnetic field lines define the direction in which a free north pole would move; the number of field lines in a particular region being used to indicate the relative strength of the field at the point in question.

In the case of the field around a straight conductor, the lines of flux are concentric and the direction of the field can be determined by application of the Right-hand Screw Rule.

The right hand screw rule will help you to remember the direction of the field. It works as follows: Think of a wood screw. To screw this into a plank of wood you have to screw to the right - it will then move into the wood. The direction of rotation is the same as the direction of the magnetic field. The direction of movement is the same as the direction of the current.

Current flowing from A to B

Current flowing from B to A

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