Two identical cells each of emf 1.5 V are connected in parallel across a parallel combination of two resistors each of resistance $20 \Omega$. A voltmeter connected in the circuit measures 1.2 V . The internal resistance of each cell is

JEE Main · 2022 · 24 Jun 2022 · Shift 1 · Current Electricity

Two identical cells each of emf 1.5 V are connected in parallel across a parallel combination of two resistors each of resistance

20Ω

. A voltmeter connected in the circuit measures 1.2 V . The internal resistance of each cell is

Answer: (C)

For two identical cells in parallel, the effective emf is 1.5 V and effective internal resistance is

r /2

. The external resistance is

20 ∥ 20 = 10Ω

.

Using

V = E - i (r /2)

1.2 = 1.5 - i (r /2)

i (r /2) = 0.3

The current

i = \frac{1.5}{10 + r /2}

, so:

10 i + i (r /2) = 1.5

10 i = 1.5 - 0.3 = 1.2

i = 0.12 A

Therefore

r = \frac{0.6}{0.12} = 5Ω

JEE Main · 2022 · 24 Jun 2022 · Shift 1 · Single correct option