# Step response of Series RLC circuit

Can we solve this question by using KVL to derive characteristic equation and passive sign convention at t>0 rather than using derived formule. p.s. the response I(t) is underdamped.

I am having difficulty in assigning direction of voltage to inductor cuz going by passive sign convention for directions of inductor, I am getting a overdamped circuit.

THANKS :-)

• The inductor induced emf, $\small L\frac{di}{dt}$, opposes the current arrow. $\small \zeta =0.9$, so just south of critically damped. – Chu Jun 22 at 13:40
• It shouldn't matter which direction you chose for a voltage or current, as long as you are comfortable with negative values for voltage or current. It all works out in the end. – Elliot Alderson Jun 22 at 18:37
• It will as I am getting my result as overdamped in place of having a underdamped circuit. – Derek Jun 22 at 20:24
• as long as your convention is consistent, then it should not change the answer... the fact that you are getting a different answer should lead you to check the proper signs for all the other factors as well so they lead to the correct solution. – Juan Jun 24 at 7:32