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JEE Main 2021 (27 Aug, Shift 1) · Cells: EMF, Internal Resistance & Combinations

Cells: EMF, Internal Resistance & Combinations question from JEE Main 2021 (27 Aug, Shift 1)

Q27JEE Main 2021 · 27 AUG · SHIFT 1Medium

Cells: EMF, Internal Resistance & Combinations

Five identical cells each of internal resistance 1 $\Omega$ and emf 5V are connected in series and in parallel with an external resistance 'R'. For what value of 'R', current in series and parallel combination will remain the same?

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Answer: (a)

Series: $I_s = \dfrac{5E}{R + 5r} = \dfrac{25}{R + 5}$ .
Parallel: $I_p = \dfrac{E}{R + r/5} = \dfrac{5}{R + 0.2}$ .
$I_s = I_p \Rightarrow 25(R + 0.2) = 5(R + 5) \Rightarrow 20R = 20$
So the answer is (a) $R = 1\ \Omega$ .

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