CBSE 2024 · Region 1 · Set 2 · Q17 · 2 marks
Two batteries of emfs $\displaystyle 6$ V and $\displaystyle 3$ V and internal resistances $\displaystyle 0 \cdot 8 \Omega$ and $\displaystyle 0 \cdot 2 \Omega$ respectively are connected in series to an external resistance $\displaystyle R$, as shown in figure. Find the value of R so that the potential difference across the $\displaystyle 6$ V battery be zero.
Marking-scheme solution
\[i=\frac{9}{R+1}
\] As potential difference across 6V is zero;
\[6-\mathrm{ir}=0 \Rightarrow 6-\left(\frac{9}{R+1}\right)(0.8)=0
\] On solving;
\[R=0.2 \Omega
\]
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