Question

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

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

Answer 1

The correct option is B $0.5$

Given data,

Internal resistance $E=2.1V$

Current $I=0.2A$

Resistance $R=10$

Find $r=?$

$I=\frac{E}{R+r}$

$0.2=\frac{2.1}{10+r}$

$2+0.2r=2.1$

$0.2r=2.1$

$r=0.5$