A solid aluminium disc of radius 0.10 m and thickness 5 mm is held with its flat face perpendicular to a magnetic field whose magnitude varies harmonically with time while its amplitude remains fixed.
(i) State Lenz’s law of electromagnetic induction.
(ii) Using Lenz’s law, explain why circulating currents are produced in the disc when the field changes with time.
(iii) The frequency of the field is increased from 2 kHz to 10 kHz without altering its amplitude. Qualitatively discuss how this change affects (1) the induced emf in the disc, (2) the current density inside the metal, and (3) the rate at which the disc is heated.
(iv) Mention any two practical steps that can be taken to reduce unintentional heating of such a disc placed in a rapidly varying magnetic field.