Question

The potential difference across the terminals of a battery is 8.5 V when there is a current of 3A in the

battery from the negative to the positive terminal. When the current is 2A in the reverse direction, the

potential difference becomes 11 V. The internal resistance of the battery is

(A) 2.5 W (B) 5.5 W

(C) 2.83 W (D) 0.5 W

Answer 1

Let ξ be the emf of the battery and r be the internal resistance 

so V = ξ - Ir or 8.5 = ξ - 3*r or ξ = 8.5 + 3*r 

and when the current is reversed 11 = ξ + 2*r 

so 11 = 8.5 + 3*r + 2*r = 8.5 + 5*r 

so r = (11 - 8.5)/5 = 0.50Ω

Answer 2

Explanation:

internal resistance r=0.5 ohm