A cell of emf 'E ’ and internal resistance 'r ’ is connected acro… - Vidyadip

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.

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Answer

The relation between $V$ and $I$ is
$V = E – Ir$
Hence, the graph, between $V$ and $I,$ has the form shown below.

For point $A, I=0,$ Hence, $V_A= E$
For point $B, V=0,$ Hence, $E=I_Br$ Therefore, $\text{r} =\frac{\text{E}}{\text{I}_{B}}$
Alternate Answer
Emf $(E)$ equals the intercept on the vertical axis. Internal resistance $(r)$ equals the negative of the slope of the graph.

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