A current produces a magnetic field (spec 6.8, 6.10P)
Right-hand grip rule.
Whenever a current flows through a conductor, a MAGNETIC FIELD is produced around it.
Field around a straight wire β concentric circles centred on the wire. Direction given by the right-hand grip rule: grip the wire with your right hand, thumb pointing in the direction of CONVENTIONAL current; your fingers then curl in the direction of the field lines.
Field around a flat coil (single loop) β circular field lines that go THROUGH the coil in one direction inside it, loop around the wire and return on the outside. The coil acts like a tiny bar magnet with N and S faces.
Field around a solenoid (long coil with many turns) β strong, uniform field along the AXIS inside the coil; outside, the field looks like a bar magnet's (lines emerge from the N end, loop around and return to the S end). The solenoid's pole at each end is determined by the current direction (looking at the end, anticlockwise current β north pole).
These three field patterns are all required Paper 2 sketches (spec 6.10P).
- Current β field; right-hand grip rule for direction.
- Straight wire: concentric circles.
- Solenoid: bar-magnet-like external field, uniform inside.