Question 369 of 380

A $10 \text{V}$ battery with internal resistance $\text{1} \Omega$ and a $15 \text{V}$ battery with internal resistance $0.6\Omega$ are connected in parallel to a voltmeter (see figure). The reading in the voltmeter will be close to:

A$11.9V$B$13.1V$C$12.5V$D$24.5V$

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Answer: (B) $13.1V$

The equivalent emf of the battery parallel combination is given as

Equation $=\dfrac{\dfrac{{E}_{1}}{{r}_{1}}+\dfrac{{E}_{2}}{{r}_{2}}}{\dfrac{1}{{r}_{1}}+\dfrac{1}{{r}_{2}}}$

$=\dfrac{\dfrac{10}{1}+\dfrac{15}{0.6}}{\dfrac{1}{1}+\dfrac{1}{0.6}}=\dfrac{10+\dfrac{150}{6}}{1+\dfrac{10}{6}}$

$=\dfrac{105}{8}$

$=13.1V$

$∴$ The reading measured by voltmeter $=13.1V$