Question

A cell of e.m.f. $R$, then p.d. across cell is . The internal resistance of cell will be

• A. $\frac { ( E - V ) R } { E }$
• B. $\frac { ( E - V ) R } { V }$
• C. $\frac { ( V - E ) R } { V }$
• D. $\frac { ( V - E ) R } { E }$

Answer 1

Answer: (B)

$\frac { ( E - V ) R } { V }$

Answer 2

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

Across the cell,

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