Question

A cell of emf 'E' and internal resistance r is connected across a variable resistor 'R'. Plot a graph showing variation of terminal voltage 'V' of the cell versus the current 'I'. Using the plot, show how the emf of the cell and its internal resistance can be determined.

Answer 1

Given: A cell of emf ${}^{\prime }{E}^{\prime }$ and internal resistance $r$ is connected across a variable resistor ${}^{\prime }{R}^{\prime }$.

To find: Plot a graph showing variation of terminal voltage ${}^{\prime }{V}^{\prime }$ of the cell versus the current ${}^{\prime }{I}^{\prime }$. Using the plot, show how the emf of the cell and its internal resistance can be determined.

Solution:

The relation between $V$ and $I$ is given by:

$V=E-Ir$

Thus the graph between $I$ and $V$ is ass shown in fig(i).

Emf is given by the intercept on the vertical axis, i.e., the $V$-axis.

Internal resistance is given by the slope of the line i.e., slope of $V$ vs $I$ graph.