The correct answer is D: Induction.

An energy meter operates on the principle of electromagnetic induction. It measures the amount of electrical energy consumed over a specific period (in kWh) and is essential for utility billing.

How it works:

• Voltage Coil: Connected across the load; produces a magnetic field proportional to the applied voltage.

• Current Coil: Connected in series with the load; generates a magnetic field proportional to the current through the load.

• Interaction of Magnetic Fields: The interaction between these two magnetic fields induces eddy currents in an aluminum disc, creating a torque that causes the disc to rotate.

• Disc Rotation: The rotational speed of the aluminum disc is directly proportional to power consumption — higher power means faster rotation.

• Counting Mechanism: The disc rotation drives a gear mechanism that translates rotation into a numerical display of energy consumed in kilowatt-hours (kWh).