- #1

psparky

Gold Member

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- 32

**AC vs DC!!!!**

The intent of this post is mostly for aspiring students:

When working with one of my students recently….I notice he tends to freak out between the difference of AC and DC……Like they are two completely different subjects. He says one has a frequency and the other doesn’t. I say not true….they all have many different frequencys….just in DC that frequency (ω) happens to be zero.

They are relatively the same in my mind. Other than the fact that maybe AC must be put in RMS before finding most results. And yes, AC is an alternating current….but it means very little for problem analysis.

The following formulas and processes apply to AC and DC:

V=IR

P=IV

V^2/R=P

P=I^2*R

Votage Dividers

Current Dividers

JωL

1/JωC

The biggest hang up is the capacitor and inductor. The sight of these in AC is enough to put any aspiring student in a complete frenzy. Why? In DC you are still using JωL and 1/JωC are you not? Right? Same for AC. Again, all those formulas above work for AC and DC. How could they not?

The only difference in AC is that you will have a reactance vector with magnitude and direction if there is an inductor or capacitor in the problem. You should know basic j plane addition and basic polar vector multiplication I would hope.

In DC…..V=IR

In AC…..V(ω)=I(ω)*R(ω)……and come to think of it….this is really the formula for DC….just the ω=0!

You work all the problems the same…..and yes….they can both shock the crap out of you!!

Please stop putting AC and DC into two different categories. Yes, they have some differences……….but 95% of the rules apply to both equally!!!

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