Question: Q. 14. The plot of the variation of potential difference across a combination of three identical cells in series, versus current is shown below. What is the emf and internal resistance of each cell?
R [O.D. I, II, III 2016]
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Solution:
Ans. Yoltage across cell combination
$$ \begin{align*} & \qquad V=E-I r \ & \text { When current } \quad I=0 \Rightarrow V=E \ & \text { From graph, when } I=0, V=6 \mathrm{~V} \Rightarrow \operatorname{emf} E=6 \mathrm{~V} \ & \text { As } \ & \qquad \begin{align*} \therefore V=E-I r \Rightarrow 0=6 & -I r \Rightarrow-6=-I r \ r & =6 \Omega \end{align*} \end{align*} $$
