Question

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

• A. $0.2\Omega$
• B. $0.5\Omega$
• C. $0.8\Omega$
• D. $1.0\Omega$

Answer 1

Answer: (B)

$0.5\Omega$

$I=\frac{E}{R+r}$
$0.2\times (10+r)=2.1$
$10+r=\frac{2.1}{2}\times 10$
$r=10.5-10=0.5\Omega$