When a certain a.c supply is connected to a lamp; it lights with the same brightness as it does with a 12 V d.c battery. Then r.m.s value of the a.c supply is?

A. 12.0 V
B. 3.5 V
C. 17.0 V
D. 8.5

Correct Answer:

Option A = 12.0 V

Explanation

The r.m.s value of an a.c voltage/current is the value of the d.c. voltage/ current that will dissipate the same amount of energy in a given resistance as the a.c. Thus the r.m.s value of the a.c supply is 12v.