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Question: Answered & Verified by Expert
A cell of e.m.f. $E$ is connected with an external resistance $R$, then p.d. across cell is $V$. The internal resistance of cell will be
PhysicsCurrent ElectricityJEE Main
Options:
  • A $\frac{(E-V) R}{E}$
  • B $\frac{(E-V) R}{V}$
  • C $\frac{(V-E) R}{V}$
  • D $\frac{(V-E) R}{E}$
Solution:
2364 Upvotes Verified Answer
The correct answer is: $\frac{(E-V) R}{V}$
Let the current in the circuit $=i=\frac{V}{R}$
Across the cell,
$E=V+i r \Rightarrow r=\frac{E-V}{i}=\frac{E-V}{V I R}=\left(\frac{E-V}{V}\right) R$

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