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Time Response of Reactive Circuits - Technical MCQs

Q1:

If the pulse source has an internal resistance of 80 omega.gif in the given circuit, it will take ______ for the output voltage to decrease to zero.

A 1 ms

B 1.1 ms

C 1.2 ms

D 2.5 ms

ANS:B - 1.1 ms

Formula for TC(Time Constant) = L/R.

But since the source has an internal resistance it can be added in series with the 820 Ω resistor.
For the output voltage to decrease to zero it needs 5 Time Constants or simply 5*TC.
Rs = 820 Ω + 80 Ω = 900 Ω,
TC = (200mH/900 Ω) = 222.22μs,
5*TC = (5)(222.22μs) = 1.111ms.