Current flowing through the cell and potential difference between its two poles obtained by obtained observations, observation table has been prepared. The internal resistance of cell is r.

order	V volt	I Ampiere
1	1.0	0.08
2	0.5	0.18
3	0.8	0.12

Find the emf of the cell used in experiment.

(B)
\(\begin{array}{l} V =\varepsilon- I r \\ \therefore \quad \varepsilon= V + I r\end{array}\)
Substituting value of V and I from 1 and 2 row of the observation table.
\(\therefore \varepsilon=1+0.08 r\) \(\quad \quad \ldots \ldots(1)\)
and \(\varepsilon=0.5+0.18 r\) \(\quad \quad \ldots \ldots(2)\)
compare equation (1) with equation (2)
\(0.5+0.18 r =1+0.08 r \\ \therefore 0.18 r-0.08 r =1-0.5 \\ \therefore 0.1 r =0.5 \\ =5 \Omega\)
Now \(\varepsilon= V + I r\)
\(\begin{array}{ll}\therefore \varepsilon=1+0.08 \times 5(\because r=5 \Omega) \\ \therefore \varepsilon=1+0.4 \\ \therefore \varepsilon=1.4 V\end{array}\)