Question

two permanent magnets are put onto a mass scale with unlike poles facing each other. a wire of length 40cm is put between the current of 0.653A is applied. magnetic flux density is 0.02T and the force produced is upwards. what mass would the scale read if it was set to zero before the current turned on

Answer 1

Ampere’s force is F = ILB, the same force acts on the magnetic field according to Newton’s third law, therefore $m = \frac{ILB}{g} = \frac{0.4\cdot0.653\cdot0.02}{10} = 0.5 (g).$