6.3 - Electromagnetism
The magnetic field around a current-carrying wire
- Whenever an electric current flows through a wire, a magnetic field is created around it.
- Around a long, straight current-carrying wire the field is made up of concentric circles, lying in planes perpendicular to the wire, with the wire at their centre.
- This pattern can be shown with small plotting compasses placed around the wire: as current flows, each compass lines up along a circle, tracing the field direction.
The right-hand thumb rule
- Point the thumb of the right hand in the direction of the current and curl the fingers around the wire.
- The fingers then point in the direction of the magnetic field.
- Reversing the current reverses the field.
Field strength
The field strength depends on two things:
- Size of the current - A larger current produces a stronger field.
- Distance from the wire - The field is stronger closer to the wire and weaker further away.