Problem 10: A source of what potential difference is needed to charge a battery of 20V e.m.f and internal resistance of 0.1Ω at a rate of 70A?

Solution:

Step: 1 Overview

Internal resistance of a battery:
When a current flows in a battery, it encounters some resistance by the electrolyte present between its two electrodes. This resistance is known as the internal resistance of the battery and is denoted by "r".
During charging a battery:

V=E+Ir

During discharging a battery:

V=E-Ir

Step: 2 Calculation

Given:

E=20V
r=0.1Ω
I=70A

Required:

V=?

Solution:

We know that during charging a battery:
V=E+Ir
V=20+70(0.1)
V=20+7
V=27V (Ans)