Question

A battery of e.m.f. 3.0 V supplies current through a circuit in which the resistance can be changed. A high resistance voltmeter is connected across the battery. When the current is 1.5 A, the voltmeter reads 2.7 V. Find the internal resistance of the battery.

Answer 1

$ϵ=3V$
$I=1.5A$
$V=2.7V$
$V=ϵ-Ir$
$r=\frac{ϵ-V}{I}$
$r=\frac{3-2.7}{1.5}=0.2\Omega$