Question

In an electric circuit, a call of certain emf provides a potential difference of $1.25V$ across a load resistance of $5\Omega$. However, it provides a potential difference of $1V$ across a load resistance of $2\Omega$. The emf of the cell is given by $\frac{x}{10}V$. Then the value of $x$ is_______.

Answer 1

Answer: 15

Terminal voltage $v=iR=\frac{ER}{R+r}$
$1^{st}\to 1.25=\frac{E(5)}{5+r}\dots \dots$ (i)
$2^{\text{nd }}\to 1=\frac{E(2)}{2+r}\dots \dots$ (ii)
By (i) and (ii)
$r=1\Omega ,E=\frac{3}{2}V=\frac{15}{10}$ volt
$\Rightarrow x=15$