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Two cells of emfs 1 V and 2 V and internal resistance 2 Ω and 1 Ω, respectively connected in parallel, gave a current of 1 A through an external resistance. If the polarity of one cell is reversed, then value of current through the external resistance will be α/5 A. The value of α is ______.

Asked in JEE Main 6th April 2nd Shift 2026 · Combination of cells

Answer: 3

Step-by-step solution

Parallel cells act as one cell: E_eq=(E₁/r₁+E₂/r₂)/(1/r₁+1/r₂), r_eq=(r₁r₂)/(r₁+r₂)=2/3 Ω.

Both cells aligned: E_eq=(0.5+2)/(1.5)=5/3 V.

1=(5/3)/(R+2/3) gives R=1 Ω.

One cell reversed: E_eq=(2-0.5)/(1.5)=1 V, r_eq unchanged.

I=1/(1+2/3)=3/5 A, so α=3.

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