1. Chapter 22 – Alternating Current Part 1
2/18/2019
PHY-2054
J. B. Bindell
Chapter 22 – Alternating Current Part 1

2. Upcoming items for your consideration
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.

3. 3 (similar or exactly from past.)
Exam STructure
Question Number
Section 003
Section 004 1
Multiple Choice (5)
2 (seen before)
2-Wire Problem – Different currents in each class and different from the quiz
3 (similar or exactly from past.)
Inverted coil problem.
Coil problem from class.
4 (New)
Charged particle orbit.
Electron & proton in same orbit.

4. We will retain this schedule.
PHY2054 Problem Solving/Office Hours Schedule
Room MAP-318
Monday
Tuesday
Wednesday
Thursday
Friday
Bindell
8:30-9:15AM
11:00-12:00PM
10: :15 AM*
10:30-11:30AM
Dubey
12:00-1:00PM
1:30-2:45PM
These sessions will be used both for office hours and problem solving. Students from any
section of 2054 are invited to stop by for assistance in course materials (problems, etc.)
Note: There will be times when the room may not be available. In that case we will use our individual offices.
* In Office
Dr. Dubey's hours are for problem solving only.
If something else is going on in the room, come to my office!
If I am not there …. come to my office.

5. OK … How was the test?
Easy OK
Difficult
Impossible

6. How did you do?
great
less than stellar ok
poor
bombed

7. This time I did better than last time about the same as last time
worse than last time

8. ac generator

9. “Output” from the previous diagram

11. Nuclear

12. DC /AC

13. home generators
FUEL

14. what works on ac?
EVERYTHING!

15. AC -All is “in-phase”

16. But not always! (capacitor)

17. Let’s talk about phase y=f(x)=x2

18. y=f(x-2)=(x-2)2 y x2
(x-2)2 2 x

19. the “rule” 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!

20. The Sine

21. 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)

22. For the future

23. 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.

24. phasor

25. oops – the ac phaser

26. the resistor

27. Phasor diagram
Pretty Simple, Huh??

28. here comes trouble ….
We need the relationship between I (the current through)
and vL (the voltage across) the inductor.

29. From the last chapter:
HUH??*
* unless you have taken calculus.

30. check it out---

31. so-
cancel
When Dt gets very small,
cos (wDt) goes to 1. ??

33. 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)

34. result

35. (wL) looks like a resistance
Resistor
inductor
(wL) looks like a resistance
XL=wL
Reactance - OHMS
comparing

36. slightly confusing point
We will use the CURRENT as the basis for calculations and express voltages with respect to the current.
What that means?

37. back to the phasor thing

38. 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,

39. capacitor phasor diagram

40. NOTICE THAT The voltage lags the current by 90 deg
I and V are represented on the same graph but are different quantities.

41. SUMMARY