Q87 / 90 · JEE Main 2023 (11 Apr Shift 2) · Physics

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

Correct answer: 5

Solution

Let $R_{1} = 10 Ω$ .

Using $V = i R$

$i = (\frac{3}{10 + 2 r})$

The voltmeter reading is $V' = 1.5 V$ .

Thus,
$i R_{1} = V' \Rightarrow 10 \times \frac{3}{10 + 2 r} = 1.5$
$\Rightarrow 20 = 10 + 2 r$
$\Rightarrow 2 r = 10$
$\Rightarrow r = 5 Ω$

Hence, the correct answer is 5.