Question

A current of 3 A passes through an electric circuit for 5 minutes and does a work of 900J. What is the emf of the source?

(a) 3V

(b) 1V

(c) 5V

(d) 10V

The question was posed to me in class test.

This interesting question is from Current Electricity topic in division Current Electricity of Physics – Class 12

Answer 1

Right answer is (b) 1V

Easiest explanation: Current = 3 A; Time taken = 5 minutes = 300 seconds

Work done = 900 J; Power = \(\frac {Work \, done}{Time \, taken} = \frac {900}{300}\) = 3 W

Power = Voltage (emf) x Current  →  Emf = \(\frac {Power}{Current} = \frac {3}{3}\) = 1V

Therefore, the emf of the source is 1 volt.