why does L1 and C1 get removed at t

why does L1 and C1 get removed at t<0

Use the circuit below to solve this problem. The switch was closed for a long time, and then was opened at t = 0. Find i_0(20[ms]). V_s1(t) = 37 cos (570[rad/s]t-72degree)[v].

Solution

At t<0, i.e before switch got opened the circiut is in steady state. At steady state Capacitor acts as open circuit and inductor act as short circuit. As the branch with L1 & C1 does not allow current to flow, L1 & C1 gets removed.

But in A.C analysis we consider both steady state analysis and transient state analysis.

In transient state analysis i.e at t=0, here C1 acts as short circuit and L1 acts as open circuit.

So in bpth states L1 and C1 branch does\'nt allow current, So they can be removed.