3.7.5.1
Flux lines show direction and strength at the same time
Magnetic Fields & Forces — AQA A-Level Physics
- Flux lines always run from the north pole to the south pole.
- The tangent to a flux line at any point gives the direction of force a free magnetic north pole would feel there.
- Lines closer $together = stronger field. Lines further apart = weaker field$.
- Flux lines never cross. Crossing would mean two field directions at the same point, which is impossible.
- Around a bar magnet, the flux densityMass per unit volume of a material. Measured in kg m⁻³. is highest right at the poles, where lines bunch most tightly.
Bar magnet field lines
A bar magnet with flux lines curving from the north pole to the south pole. Lines are densest at the poles. Arrows point from N to S.
Examiner Tips and Tricks
- You should already know the right-hand grip rule and how to draw flux lines around wires and solenoids from GCSE.
- AQA does not re-teach this at A-Level.