Question

In A.C. circuits, power consumed is ________

(a) product of voltage and current

(b) it depends on the p.f. of the circuit in addition to voltage and current

(c) it depends on the supply voltage

(d) it depends on the magnitude of the circuit current

The question was asked during a job interview.

This interesting question is from Dynamometer Type Wattmeter in portion Measurement of Power and Related Parameters of Electrical Measurements

Answer 1

Correct option is (b) it depends on the p.f. of the circuit in addition to voltage and current

For explanation: In a A.C. circuit, the power consumption is given by the expression,

P = VI cos∅

where, V is the voltage across the circuit

        I is the current flowing through the circuit

        cos∅ is the power factor of the circuit.