A 10V battery with internal resistance 1 Ω and a 15V battery with internal resistance 0.6 Ω are connected in parallel to a voltmeter (see figure). The reading in the voltmeter will be close to: (a) 11.9 V (b) 12.5 V (c) 13.1 V (d) 24.5 V

Answer: (c). An ideal voltmeter draws no current, so it reads the equivalent emf of the parallel cells. Eeq = (E₁/r₁ + E₂/r₂)/(1/r₁ + 1/r₂) = (10/1 + 15/0.6)/(1 + 1/0.6) Eeq = (10 + 25)/(2.667) = 13.1 V So the answer is (c) 13.1 V.

A 10V battery with internal resistance 1 Ω and a 15V battery with… | JEE Main 2015 (10 Apr, Shift 1)

Q39JEE Main 2015 · 10 APR · SHIFT 1Medium

Cells: EMF, Internal Resistance & Combinations

A 10V battery with internal resistance 1 $\Omega$ and a 15V 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:

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Answer: (c)

An ideal voltmeter draws no current, so it reads the equivalent emf of the parallel cells.
$E_{eq} = \dfrac{E_1/r_1 + E_2/r_2}{1/r_1 + 1/r_2} = \dfrac{10/1 + 15/0.6}{1 + 1/0.6}$
$E_{eq} = \dfrac{10 + 25}{2.667} = 13.1\text{ V}$
So the answer is (c) 13.1 V.

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