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
Verified Correct Answer: A.
Physical Principles & Numerical Solution
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.
Source: Myschool Past Questions Archive (Record #13868)