A plotting compass is held close to a bar magnet and in line with its long axis. The magnet is turned end-for-end about its centre without moving the compass. The compass needle turns through half a turn and settles again.
Which explanation is correct?
The compass needle is demagnetised by the turn, then becomes an induced magnet with its poles exchanged.
The magnetic field at the compass becomes stronger, so the needle turns to display the increased field strength.
The magnetic field at the compass reverses direction, so the needle turns to align with the new field direction.
Both ends of the compass needle are attracted to the nearer pole, so the needle rotates as the magnet is turned.