When an external resistance of $5 \Omega$ is connected across terminals of a cell, a current of 0.25 A flows through it. When the $5 \Omega$ resistor is replaced by a $2 \Omega$ resistor, a current of 0.5 A flows through it. The internal resistance of the cell is ______ $\Omega$.

JEE Main · 2026 · 05 Apr 2026 · Shift 2 · Current Electricity

When an external resistance of

5Ω

is connected across terminals of a cell, a current of 0.25 A flows through it. When the

5Ω

resistor is replaced by a

2Ω

resistor, a current of 0.5 A flows through it. The internal resistance of the cell is ______

Ω

Answer: 1

For a cell of emf

ε

and internal resistance

r

driving a current

i

through an external resistance

R

i = \frac{ε}{R + r}

. With

R = 5 Ω

and

i = 0.25 A

ε = 0.25 (5 + r)

; with

R = 2 Ω

and

i = 0.5 A

ε = 0.5 (2 + r)

. Equating the two,

0.25 (5 + r) = 0.5 (2 + r)

, so

1.25 + 0.25 r = 1 + 0.5 r

, giving

0.25 = 0.25 r

. The internal resistance of the cell is

1 Ω

JEE Main · 2026 · 05 Apr 2026 · Shift 2 · Integer answer