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MCQEasyJEE 2026Self & Mutual Inductance

JEE Physics 2026 Question with Solution

Figure shows the circuit that contains three resistances (9 Ω9\,\Omega each) and two inductors (4 mH4\,mH each). The reading of ammeter at the moment switch KK is turned ON, is _____ A.

Circuit with a 9 V battery, switch K, ammeter A, three 9 ohm resistors, and two 4 mH inductors arranged in parallel branches.
  • A

    zero

  • B

    22

  • C

    33

  • D

    11

Answer

Correct answer:A

Step-by-step solution

Standard Method

Given: The circuit contains three resistances of 9 Ω9\,\Omega each and two inductors of 4 mH4\,mH each. The ammeter reading is required at the instant the switch KK is turned ON.

Find: The current through the ammeter at t=0t=0.

At the instant a DC circuit is switched ON, an inductor opposes sudden change in current and behaves like an open circuit.

Therefore, at t=0t=0, both branches containing inductors are effectively open. This breaks the conducting paths involving those branches, and no closed current path exists through the ammeter.

So,

I=0I = 0

Therefore, the ammeter reading at the moment the switch is turned ON is 0 A0\,\text{A}. The correct option is A.

Common mistakes

  • Treating the inductor as a short circuit at t=0t=0 is incorrect. Just after switching ON, current through an inductor cannot change abruptly, so it behaves like an open circuit. Use the initial-time behavior, not the steady-state behavior.

  • Calculating current using only the resistors and ignoring the inductors is wrong because the question asks for the instant the switch is turned ON. At that instant, the inductor branches are broken, so the current path must be checked again before applying Ohm's law.

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