Q.37. A voltmeter of resistance 150Ω connected across a cell of e.m.f. 3 V reads 2.5 V. What is the internal resistance of the cell?
A. 10Ω
B. 15Ω
C. 20Ω
D. 30Ω
Answer – D. 30Ω
Explanation :-
Internal resistance,
r=\left [ \frac{E}{V} -1\right ]R r=\left [ \frac{3}{2.5} -1\right ]R \times 150 E = 30 \Omega