An electric cell with nominal voltage E has a resistance of 3Ω connected across it. If the voltage falls to 0.6E; the internal resistance of the cell is?

A. 1Ω
B. 2Ω
C. 3Ω
D. 4Ω

Correct Answer:

Option C = 3Ω

Explanation

I = ^V/_R = 0.6E/3 = 0.2E
Again, I = E / (R+ϒ) = E / (3+ϒ)
Divide eqn (2) by eqn (1)
^I/_I = E / (3+ϒ) x I / 0.2E
=> 0.2(3+ϒ) = 1
0.6 x 0.2ϒ = 1
∴0.2ϒ = -0.6
=> ϒ = 0.6 / 0.2 = 3Ω
ϒ = 3Ω