An electric motor rotates the rotor of a laboratory centrifuge. As the coil turns through a quarter-turn, its plane moves from being parallel to the magnetic field to being at right angles to the magnetic field.
What is the change in the resultant moment on the coil as it moves between these positions?
It stays at a maximum because the width of the coil does not change as it turns.
It stays at zero because the equal and opposite forces cancel throughout the movement.
It increases from zero to a maximum as the lines of action move further apart.
It decreases from a maximum to zero as the lines of action move closer together.
90 exam-style questions on AQA GCSE Physics 7.2 The motor effect, covering 7.2.1 Electromagnetism, 7.2.2 Fleming's left-hand rule (HT only), 7.2.3 Electric motors (HT only), and 7.2.4 Loudspeakers (HT only). Each one has a worked solution and a mark scheme showing where the marks go.