Potentail difference across the terminals of a cell was measured (in volts) against different current (in ampere) flowing through the cell. A graph was drawn, which was a straight line ABC. Using the data given in the graph determine

a. the emf, and
b. the internal resistance of the cell.

Explanation

a. When no current is drawn from a cell, potential difference
across the termnals of the cell is equal to its emf. It is clear
that emf. = 1.4 V.
b. Further, `V = epsilon - Ir or r = (epsilon - V)/(I)`
Here `epsilon = 1.4 V.` Consider any given value of potential
difference from graph, say V = 1.2 V. Current corresponding
to this potential difference is 0.04 A. So
`r = (1.4 - 1.2)/(0.04) = 5 Omega`