Time constant in RC AC and RL AC Circuits?

1. Oct 25, 2012

theBEAST

1. The problem statement, all variables and given/known data
I know that in a RC DC circuit the time constant is R*C. But what about a RC AC circuit, is it the same time constant?

Same goes with RL AC circuit, is the time constant R/L?

Thanks!

2. Oct 26, 2012

Staff: Mentor

For AC (sinusoidal) circuits we're more often interested in the "steady-state" conditions that exist for continuously applied AC signals. In this scenario the time constants "$\tau$" don't have quite the same import for signal shape that they do for transient analysis since all the steady-state circuit responses are sinusoidal too.

For AC circuits the time constant expressions are more useful for determining how a given circuit will behave at different frequencies, and $1/\tau$ represents an important "landmark" in response-versus-frequency analyses.