Two batteries of different emfs and different internal resistances are connected as shown. The voltage…
Two batteries of different emfs and different internal resistances are connected as shown. The voltage across $A B$ in volt is
Solution
$V_{A B}=$ Equivalent emf of two batteries in parallel.
$
\begin{aligned}
& =\frac{E_1 / r_1+E_1 / r_2}{1 / r_1+1 / r_2} \\
& =\frac{(6 / 1)+(3 / 2)}{(1 / 1)+(1 / 2)}=5 \mathrm{~V}
\end{aligned}
$
$\therefore$ Answer is 5 .
Analysis of Question
(i) In my opinion this is the simplest question of JEE 2011.
(ii) When no current is drawn from this equivalent battery, then
$
V_{A B}=V=E
$
Otherwise, $V=E \pm$ ir
(iii) Similar type of question was asked in JEE 1981 and cancelled paper of JEE 1997.
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