A cell of e.m.f. 1.5v is connected in series with a resistor of 3Ω. A high resistance voltmeter connected across the cell registers only 0.9v. Calculate the internal resistance of the cell?

A. 5.0Ω
B. 4.5Ω
C. 2.4Ω
D. 2.0Ω
E. 1.8Ω

Correct Answer:

Option A – 5.0Ω

Explanation

I = V/R=0.9/3 = 0.3

r = E/I =1.5/0.3 = 5.0Ω