The magnetic field around a wire
When a current flows through a conducting wire a magnetic
field is produced around the wire
The field lines are concentric circles centred on the wire. The
strength of the field depends on the current through the wire and
the distance from the wire : bigger current, stronger field; further
away, weaker field
The direction of the field is given by the right-hand grip rule :
point the thumb of your right hand along the direction of the current and
your fingers curl in the direction of the field lines. Reversing the
current reverses the field
Demonstrating the effect: place plotting compasses around a vertical wire
passing through a card. With no current the compasses all point north;
with a current they line up in a circle around the wire, and
swap direction when the current is reversed
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The field around a current-carrying wire current the field lines are CIRCLES round the wire closer together near the wire — the field is stronger there THUMB — the current FINGERS — curl round the way the field goes the RIGHT hand grip rule Point the thumb of your RIGHT hand along the current (conventional current, + to −). Your fingers then curl the way the field lines go. Reverse the current and the field reverses too. A bigger current, or being closer to the wire, both give a stronger field. A straight vertical wire with concentric circular field lines around it, arrows showing the direction, current direction marked; a right hand gripping the wire with the thumb along the current and fingers curling with the field
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In the full topic
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