A cell of emf ‘E’ and internal resistance r is connected to a variable resistance ‘R’. Plot a graph showing the variation of terminal potential ‘V’ with resistance R. Predict from the graph the condition under which ‘V’ becomes equal to ‘E’.

Solution

The formula for terminal potential is given by,
$V = \frac{E}{1 + \frac{r}{R}}$
where,
V is the terminal voltage,
E is the emf,
R is the variable resistance and
r is the internal resistance.

when $\frac{r}{R} < < 1$ , we have
$V = E$