Prob 50 - Exam#1 Afternoon

[EEVA PE]

In Camara's Power Sample Exam Prob50, Exam#1, Afternoon:

The problem asks for Thevenin's equivalent voltage, but the circuit has a capacitor in it. I have always thought one treats a capacitor as an open circuit and inductor as a short when doing Thevenin's equiv, but the solution treats the capacitor as impedance. Is this the proper way to do Thevenin's equiv? using impedance instead of resistance? I have checked all my text books and does not mention using impedance for Thevenin's equiv.

Has anyone else stumbled on this prob?

 

[benbo]

Is it an AC source? I think in that case you have to consider the impedance of the elements.

http://hyperphysics.phy-astr.gsu.edu/hbase...ric/acthev.html

I'm sure I came across this problem years ago when studying for it, but now that you mention it I don't recall. Most Thev problems I remember always had DC sources and generally just resistors. But it makes sense when you think about it -think of a circuit with a source and a capaitor. How can the equivalent resistance (impedance) for that to an AC source be zero. It might be close at high frequency, but not zero.

 

[EEVA PE]

Is it an AC source? I think in that case you have to consider the impedance of the elements.
http://hyperphysics.phy-astr.gsu.edu/hbase...ric/acthev.html

I'm sure I came across this problem years ago when studying for it, but now that you mention it I don't recall. Most Thev problems I remember always had DC sources and generally just resistors. But it makes sense when you think about it -think of a circuit with a source and a capaitor. How can the equivalent resistance (impedance) for that to an AC source be zero. It might be close at high frequency, but not zero.

The source is 10V AC connected in series with a 10 ohm resistor and then in parallel with an 60 uF Cap and in parallel with a 5 ohm resistor. The link you provided answers my question. Thanks! Therefore, the equiv Thevenin voltage can have a phase angle since we can use impedance.