Question

The internal resistance of a $2.1V$ cell which gives a current of $0.2A$ through a resistance of $10\Omega$ is _______.

• A. $0.5\Omega$
• B. $0.2\Omega$
• C. $0.1\Omega$
• D. $0.8\Omega$

Answer 1

The correct option is A $0.5\Omega$

Given, current, $I=0.2A$
Voltage, $ϵ=2.1V$
Resistance, $R=10\Omega$
Let the internal resistance be $r$.
We know, $I=\frac{ϵ}{R+r}$
or, $IR+Ir=ϵ$

$IR+Ir=ϵ$
$⟹0.2\times 10+0.2\times r=2.1$
$⟹2+0.2r=2.1$
$⟹r=0.5\Omega$