Question 187 of 380

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 $\dfrac{x}{10}V.$ Then the value of $x$ is $.$

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Answer: 15

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