Six identical cells, each of emf 3 V and internal resistance of r, are connected in series to a 3 Ω resistance. If the net current flowing in the circuit is 2.0 A. The internal resistance of the cell is

$1Ω$

The correct answer is Option (4) → $1Ω$

Given:

Number of cells $n = 6$

Each emf $E = 3 \, V \;\;\Rightarrow\;\; E_{total} = nE = 18 \, V$

Each internal resistance $= r \;\;\Rightarrow\;\; r_{total} = nr = 6r$

External resistance $R = 3 \, \Omega$

Current $I = 2 \, A$

Ohm’s law for the circuit:

$I = \frac{E_{total}}{R + r_{total}}$

$2 = \frac{18}{3 + 6r}$

$3 + 6r = \frac{18}{2} = 9$

$6r = 6 \;\;\Rightarrow\;\; r = 1 \, \Omega$

Answer: $1 \, \Omega$