Question

a cell has an e.m.f. of 3v. when it is connected across a resistor of resistance 4ohms, a current of 0.5a passes through the current. calculator the internal resistance

Answer 1

Gives $E=3V\\R=4\Omega\\i=0.5A$

We know that

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

$0.5=\frac{3}{4+r}$

$2+0.5r=3$

$r=\frac{10}{5}=2\Omega$