In the given circuit the sliding contact is pulled outwards such that electric current in the circuit changes at the rate of $8 \mathrm{~A} / \mathrm{s}$. At an instant when R is $12 \Omega$, the value of the current in the circuit will be $\_\_\_\_$ A.

JEE Main · 2025 · 23 Jan 2025 · Shift 1 · Electromagnetic Induction

In the given circuit the sliding contact is pulled outwards such that electric current in the circuit changes at the rate of

8 A / s

. At an instant when R is

12Ω

, the value of the current in the circuit will be

____

Answer: 3

Solution

Applying Kirchhoff's voltage law to the LR circuit with EMF

ε = 12 V

and inductance

L = 3 H

ε - L \frac{d I}{d t} - I R = 0

The current is decreasing as the resistance increases, so

\frac{d I}{d t} = - 8 A/s

. At the instant

R = 12 Ω

12 - 3 (- 8) - 12 I = 0

12 + 24 - 12 I = 0

36 = 12 I \Rightarrow I = 3 A

JEE Main · 2025 · 23 Jan 2025 · Shift 1 · Integer answer

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