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The disc of an induction energy meter is made of aluminium because it is

  • A.resistant to the heating produced by the eddy currents circulating within it
  • B.capable of retaining a permanent magnetism which assists the braking action
  • C.light and a good conductor
  • D.magnetic

Answer: C

Low density keeps the inertia and the bearing friction small, and high conductivity allows large eddy currents for a given flux. Aluminium is not magnetic, and it does not need to be: the torque comes from currents induced in it, not from attraction.

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