I want to ask that how to get the time constant for simple RCL circuit in order to get the natural response later, Here is the sample circuit. Assume that S is close at t=0 and the circuit is open for a long time
when S close, in order to calculate the time constant \$\tau\$ in this case, I omit the source \$V_S\$ but then I don't know how the circuit which will be used to calculate \$\tau\$ look like. I thought \$V_S\$ will act like sort circuit so it'll look like this
but my lecturer said it actually looked like this, which doesn't have \$R_1\$
So what is the rule when omitting the source in case of: voltage source and voltage source. What if the switch is in series but not parallel?