Field Around a Straight Wire
Field Around a Straight Wire
- Current means charge is moving. Moving charge produces a magnetic field.
- First learn the field around one straight wire. Coils and solenoids follow in the next lesson.
A long straight wire
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- The field lines are concentric circles centred on the wire.
- The circles become farther apart as distance from the wire increases. This shows that the field becomes weaker.
- Use the right-hand rule: point your right thumb along the conventional current. Your curled fingers show the field direction.
For current into the page, the field is clockwise. For current out of the page, the field is anticlockwise.
How the drawing marks are awarded
A recent straight-wire question awarded one mark for each of these features (9702/41/O/N/24 Q7(b)):
- concentric circles around the wire;
- spacing that increases with distance;
- arrows in the correct direction.
Your turnField-pattern check
A long straight wire carries current out of the page. State the field-line shape and direction.
Show worked answer
The field lines are concentric circles. The right-hand rule gives an anticlockwise direction.