When a conductor carrying a current is placed in a magnetic field the magnet producing the field and the conductor exert a force on each other. This is called the motor effect. • Students should be able to show that Fleming's left-hand rule represents the relative orientation of the force, the current in the conductor and the magnetic field. • Students should be able to recall the factors that affect the size of the force on the conductor. • For a conductor at right angles to a magnetic field and carrying a current: force = magnetic flux density × current × length, F = BIl (force, F, in newtons, N; magnetic flux density, B, in tesla, T; current, I, in amperes, A (amp is acceptable for ampere); length, l, in metres, m).