Question

A cell has a terminal voltage of 1.35 V when it is connected to a 0.9 ohm external resistor. 

When the resistance is increased to 2.4 ohm, the terminal voltage is 1.44 V. Calculate the 

internal resistance of the cell.

Answer 1

$E=V+Ir$

$V=IR$

$1.35=I(0.9)$

$I=1.5$

$\implies\>E=1.35+1.5r....$ (i)

$1.44=I(2.4)$

$I=0.6$

$E=1.44+0.6r$ ........(ii)

Equation (ii) $-$ (i)

$0.09-0.9r=0$

$r=0.1\Omega$