A resistance R is connected across the terminal of an electric cell of internal resistance 2Ω and the voltage was reduced to 3/5 of its nominal value. The value of R is?

A. 3 Ω
B. 2 Ω
C. 1 Ω
D. 6 Ω

Correct Answer:

Option A – 3 Ω

Explanation

1 = V/R = E/R+r , if r = 2Ω
V = 3/5 E
=> 3E/5R = E/R+2
i.e 3E(R+2) = 5RE
3RE + 6E = 5RE
i.e 3R + 6 = 5R
6 = 5R – 3R
=> 2r = 6 i.e R = 6/2 = 3Ω