Question

A cell of e.m.f. E is connected with an external resistance R; p.d. across the cell is v. the internal resistance of the cell will be:

• A. $(E-V)R/E$
• B. $(E-V)R/V$
• C. $(V-E)R/V$
• D. $(V-E)R/E$

Answer 1

The correct option is B $(E-V)R/V$

From ohm's law:

Let the current in the circuit $=i=\frac{V}{R}$

P.D Across the cell, $E=V+ir$

$\Rightarrow r=\frac{E-V}{i}=\frac{E-V}{V/R}=\left(\frac{E-V}{V}\right)R$