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

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The equivalent emf of the battery parallel combination is given as

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

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

$= \frac{105}{8}$

$= 13.1 V$

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

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