Question 176 of 380

Two identical cells each of emf $1.5V$ are connected in series across a $10\Omega$ resistance. An ideal voltmeter connected across $10\Omega$ resistance reads $1.5V$. The internal resistance of each cell is _____ $\Omega$.

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Answer: 5

Let ${R}_{1}=10\Omega$.
Using $V=iR$
$i=\left(\dfrac{3}{10+2r}\right)$
The voltmeter reading is $V'=1.5V$.
Thus,
$i{R}_{1}=V' \Rightarrow 10\times \dfrac{3}{10+2r}=1.5$
$\Rightarrow 20=10+2r$
$\Rightarrow 2r=10$
$\Rightarrow r=5\Omega$