Question

The emf of a cell is ℰ and its internal resistance is r. Its terminals are connected to a resistance R. The potential difference between the terminals is 1.6 V for R = 4 Ω, and 1.8 V for R = 9 Ω. Then,

(a) ℰ = 1 V, r = 1Ω 

(b) ℰ = 2 V, r = 1Ω 

(c) ℰ = 2 V, r = 2Ω 

(d) ℰ = 2.5 V, r = 0.5Ω

Answer 1

Correct Answer is: (b) ℰ = 2 V, r = 1Ω 

Current in the circuit = i = ℰ / R + r.

p.d. across cell = p.d. across R = iR = ℰR/R + r.

Set up two equations with the given data and solve for ℰ, r.