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PHY-2054 J. B. Bindell. Chapter 22 – Alternating Current Part 1. No problem session on Monday (Not much to do!) Watch for a Mastering Physics Assignment Quiz next Friday on AC … will it ever end? Today we start AC Circuits We will review the exam when they are returned.
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PHY-2054 J. B. Bindell Chapter 22 – Alternating CurrentPart 1
No problem session on Monday (Not much to do!) Watch for a Mastering Physics Assignment Quiz next Friday on AC … will it ever end? Today we start AC Circuits We will review the exam when they are returned. Upcoming items for your consideration
We will retain this schedule. If something else is going on in the room, come to my office! If I am not there …. come to my office.
Easy OK Difficult Impossible OK … How was the test?
great less than stellar ok poor bombed How did you do?
better than last time about the same as last time worse than last time This time I did
home generators FUEL
what works on ac? EVERYTHING!
y=f(x-2)=(x-2)2 y x2 (x-2)2 2 x
f(x-b) shift a distance b in the POSITIVE direction f(x+b) shift a distance n in the NEGATIVE direction. The signs switch! the “rule”
Let’s talk about PHASE f(t)=A sin(wt) A=Amplitude (=1 here) f(t)=A sin(wt-[p/2]) A=Amplitude (=1 here)
AC Applied voltages This graph corresponds to an applied voltage of V cos(wt). Because the current and the voltage are together (in-phase) this must apply to a Resistor for which Ohmmmm said that I~V.
Phasor diagram Pretty Simple, Huh??
here comes trouble …. We need the relationship between I (the current through) and vL (the voltage across) the inductor.
From the last chapter: HUH??* * unless you have taken calculus.
so- cancel When Dt gets very small, cos (wDt) goes to 1. ??
this leaves The resistor voltage looked like a cosine so we would like the inductor voltage to look as similar to this as possible. So let’s look at the following graph again (~10 slides back): f(t)=A sin(wt) A=Amplitude (=1 here) f(t)=A sin(wt-[p/2]) A=Amplitude (=1 here)
Resistor inductor (wL) looks like a resistance XL=wL Reactance - OHMS comparing
slightly confusing point We will use the CURRENT as the basis for calculations and express voltages with respect to the current. What that means?
What about the capacitor?? Without repeating what we did, the question is what function will have a Df/Dt = cosine? Obviously, the sine! So, using the same process that we used for the inductor,
The voltage lags the current by 90 deg I and V are represented on the same graph but are different quantities. NOTICE THAT