099 Simple Motor



First note that an electric current is flowing from the external wire, through the magnet, into the screw.

This current is sitting in the magnetic field of the magnet. (In fact, it is the field inside the magnet)

There is thus a F=BIL force acting on that part of the magnet which carries the current. This results in a net torque about the centre of mass of the magnet, which causes the magnet to rotate.

Alternatively, you can think of it as charges in the magnet moving in the magnet’s magnetic field. You will then be thinking of F=Bqv forces acting on the moving charges, which will result in the same spinning motion.

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