The AC voltage across a resistance can be measured using a
A) moving magnet galvanometer
B) moving coil galvanometer
C) hot wire voltmeter
D) potentiometer

Hint: The above problem can be solved by using the working principle of the moving magnet galvanometer, moving coil galvanometer, hot wire voltmeter and potentiometer. The moving magnet galvanometer and moving coil galvanometer is based on the electromagnetic effect of the coil. The hot wire voltmeter is based on the variation in the resistance of the wire with temperature. The potentiometer is based on the variation in the resistance with the length of the wire.

Complete step by step answer:
The moving magnet galvanometer and moving coil galvanometer measures the voltage of the DC supply because the galvanometer does not show any deflection in the reading for the AC supply, so the option (A) and option (B) is incorrect.
The alternating current produces the heat when it passes through a resistor. The variation in the temperature of the hot wire of the hot wire voltmeter measures the AC voltage, so the option (C) is correct.
The potentiometer is the electrical instrument that measures the internal resistance and emf of the unknown battery, so the option (D) is incorrect.

Additional Information:
 The moving magnet galvanometer and moving coil galvanometer measures the induced emf of the coil and magnet due to variation in the magnetic field of the coil and magnet. The potentiometer measures the resistance by measuring the change in the length of the unknown wire.

Note: Carefully study the working principle of moving magnet galvanometer, moving coil galvanometer, hot wire voltmeter and potentiometer before solving the problem.