Upon a six fold increase in the external resistance of a circuit, the voltage across the terminals of the battery has increased from 5V and to 10 V. The emf of the battery
Answer & explanation
Correct answer: option 3
Voltage across terminal of a battery is $V = E - Ir = E - \frac{Er}{r+R} = \frac{ER}{r+R}$
$\Rightarrow \frac{ER}{r+R} = 5V$ ..............(1)
According to question $\frac{6ER}{r+6R} = 10$.......(2)
On dividing $\frac{6r+6R}{r+6R} = 2 \Rightarrow 6r+ 6R = 2r + 12R$
$ \Rightarrow r = 1.5R$
$ E = 12.5V$