Question

A cell of e.m.f. 2.1 V gives a current of 0.2 A. This current is passing through the resistance of 10 $\Omega$. The internal resistance of cell is :

• A. 0.2 $\Omega$
• B. 0.5 $\Omega$
• C. 0.8 $\Omega$
• D. 0 $\Omega$

Answer 1

The correct option is B 0.5 $\Omega$

$I=\frac{E}{R+r}$
$0.2=\frac{2.1}{10+r}$
$\therefore 10+r=\frac{2.1}{0.2}=\frac{21}{2}=10.5$
$\therefore r=0.5\Omega$