Question

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

Answer 1

When we say the batteries are connected in parallel with the voltmeter it means that the cells are in series.

The effective electromotive force of cells arranged in series is the sum of the emf s

The effective internal resistance if the sum of the individual internal resistance.

In this case the effective emf equals :

Effective emf = 10 + 15 = 25V

24.5 is closer 25 V. The reading is lower due some voltage lost as a result of resistance in the circuit.