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

Explanation

Here, emf=terminal voltage + internal potential drop
So, `E=V+Ir or , V=-Ir+E`
This equation is of the form y=mx+c. SO the I-V graph is a straight line of slope -r and of intercept E on the V-axis [Fig.1.115].
The emf E is known from this intercept and the internal resistance r from the slop i.e., `r=-(AB)/(BC)` in the figure.