GATE 2024 EC – Question 32
In the circuit given below, the switch S was kept open for a sufficiently long time and is closed at time $t=0$. The time constant (in seconds) of the circuit for $t>0$ is ______.
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Show answer and explanation
Correct answer: 0.74 to 0.76
Explanation
For $t>0$ the current source is an open circuit for the purpose of finding the time constant. The resistance seen by the 3 H inductor is the 2 Ω resistor on the source side in series with the two 4 Ω resistors that are now in parallel ($4\parallel4=2\ \Omega$): $R_{eq}=2+2=4\ \Omega$. So $\tau=L/R_{eq}=3/4=0.75$ s.