Question

Potential difference across a battery is 9V. On connecting a $24\Omega$ resistor across the terminals of the battery, the voltmeter reads 7.2 V. Calculate the internal resistance of the battery.

• A. $4\Omega$
• B. $6\Omega$
• C. $10\Omega$
• D. $12\Omega$

Answer 1

The correct option is B

$6\Omega$

Given,
Potential energy, E = 9 V
Voltmeter reading, V = 7.2 V
Resistace, $R=24\Omega$
From relations $E=I(R+r)$ and V = IR (Where, E= Potential difference across the battery, I = current, R = Resistance, R = Internal resistance)
$r=(\frac{ϵ}{V}-1)\times R=(\frac{9}{7.2}-1)\times 24=6\Omega$
Hence, the correct option is B.