How Do You Determine the Starting Point of Phase in Circuit Analysis?

[cutesteph]

When writing the question for the phase response of a circuit, how do I know when it begins. Like for example theta(jw) = 90 degrees - arctan( ) or theta(jw) = 0 degrees - arctan( ) ?

 

[meBigGuy]

Output phase is relative to input phase, which is arbitrary. Consider a sine wave input ... or is it a 90degree phase shifted cosine input? You define 0 on the input wherever you want to.