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MHT CET 2025 (19 Apr, Shift 2) · Cells: EMF, Internal Resistance & Combinations

Cells: EMF, Internal Resistance & Combinations question from MHT CET 2025 (19 Apr, Shift 2)

Q8MHT CET 2025 · 19 APR · SHIFT 2Medium

Cells: EMF, Internal Resistance & Combinations

Two cells E1E_1 and E2E_2 having equal e.m.f ' EE ' and internal resistances r1r_1 and r2 (r1>r2)r_2\ (r_1 > r_2) respectively are connected in series. This combination is connected to an external resistance ' R '. It is observed that the potential difference across the cell E1E_1 becomes zero. The value of RR will be

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Answer: (a)

  1. I=2ER+r1+r2I = \frac{2E}{R + r_1 + r_2}
  2. Terminal p.d. of E1E_1: E−Ir1=0⇒I=Er1E - Ir_1 = 0 \Rightarrow I = \frac{E}{r_1}
  3. 2ER+r1+r2=Er1⇒R+r1+r2=2r1\frac{2E}{R + r_1 + r_2} = \frac{E}{r_1} \Rightarrow R + r_1 + r_2 = 2r_1
  4. R=r1−r2R = r_1 - r_2. So the answer is (a).
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