Question

When a resistance of $3\Omega$ is connected across a cell, the current flowing is $0.5A$. On a changing the resistance to $7\Omega$, the current becomes $0.25A$. Calculate the e.m.f. and internal resistance of the cell.

Answer 1

Fromula for internal resistance is given by

$ϵ=I(r+R)$

for R=3 and I=0.5, $e{q}^n$ becomes

$ϵ-0.5r=1.5$

similarly for R=7 and I=0.25

$ϵ-0.25r=17.5$

solving both equation

$r=64\Omega$ and $ϵ=33.5V$