The shiny metal disc in the electric power meter (analogue type) rotates by the:

CONCEPT:

Eddy current:

• When a changing magnetic flux is applied to a bulk piece of conducting material then circulating currents called eddy currents are induced in the material.
• Because the resistance of the bulk conductor is usually low, eddy currents often have large magnitudes and heat up the conductor.
• These are circulating currents like eddies in the water.
• The experimental concept was given by Focault hence also named “Focault current”.
• The production of eddy currents in a metallic block leads to the loss of electric energy in the form of heat.
• Eddy currents are minimized by using laminations of metal to make a metal core. The laminations are separated by an insulating material like lacquer.
• Eddy currents are undesirable in the metallic cores of transformers, electric motors, and other such devices in which a coil is to be wound over a metallic core since they heat up the core and dissipate electrical energy in the form of heat.
• Eddy currents are used to advantage in certain applications like:
  1. Magnetic braking in trains
  2. Electromagnetic damping
  3. Induction furnace
  4. Electric power meters

EXPLANATION:

Electric power meters:

• The shiny metal disc in the electric power meter (analogue type) rotates due to the eddy currents.
• Electric currents are induced in the disc by magnetic fields produced by sinusoidally varying currents in a coil. Hence, option 2 is correct.