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JEE Main 2022 (29 Jun, Shift 2) · Cells: EMF, Internal Resistance & Combinations

Cells: EMF, Internal Resistance & Combinations question from JEE Main 2022 (29 Jun, Shift 2)

Q21JEE Main 2022 · 29 JUN · SHIFT 2Medium

Cells: EMF, Internal Resistance & Combinations

The combination of two identical cells, whether connected in series or parallel combination provides the same current through an external resistance of 2Ω\Omega. The value of internal resistance of each cell is

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Answer: (a)

  1. Series: I=2E2+2rI = \frac{2E}{2 + 2r}; parallel: I=E2+r/2I = \frac{E}{2 + r/2}
  2. Equal: 2(2+r2)=2+2r⇒4+r=2+2r2\left(2 + \frac{r}{2}\right) = 2 + 2r \Rightarrow 4 + r = 2 + 2r
  3. r=2 Ωr = 2\ \Omega. So the answer is (a). (In general, equal currents need r=Rr = R.)
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