CBSE Class 12 · 2023 · Current ElectricityMultiple Choice

A cell of EMF

E

is connected across an external resistance

R

. When a current

I

is drawn from the cell, the potential difference across its electrodes drops to

V

. The internal resistance

r

of the cell is:

Answer: (D)

Solution

E = V + I r \Rightarrow r = \frac{E - V}{I}

. The current is

I = \frac{V}{R}

(terminal voltage across

R

), so

r = \frac{E - V}{V / R} = (\frac{E - V}{V}) R .

CBSE Class 12 Board · 2023 · Single correct option