1. Chapter 22 – Alternating Current Part 2
5/19/2019
PHY-2054
J. B. Bindell
Chapter 22 – Alternating Current Part 2

2. the future Monday – Continue with Chapter 22 Wednesday – Friday –
Hope to return the exams.
more of the same
Friday –
Quiz
No 10:30 AM office hours (sorry)
Next Monday – Probably a problem solving session at 7:00AM. Confirmation later in the week.

3. result - inductor
I is the MAXIMUM
current in the
circuit.

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

5. Let’s put these together.
For the inductor
FOR THE RESISTOR
Let’s put these together.

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

7. the phasor

8. direction wt wt

9. remember for ac series circuits
The current is the
same throughout the
series circuit.
The Maximum Current “I”
is also the same for
all series circuit elements.

10. Compute the reactance of a 0.450 H inductor at frequencies of 60.0 Hz

11. In the circuit below, R=30 W and L= 30 mH. If the angular frequency
of the 60 volt AC source is is 3 K-Hz
WHAT WE WANT TO DO:
calculate the maximum current in the circuit
calculate the voltage across the inductor
Does Kirchoff’s Law Work?
E=60V
R=30 W
L= 30 mH
w=3 KHZ

12. I wt R=30W w=3 KHZ R=30 W XL=wL=90W E=60V
L= 30 mH
w=3 KHZ
R=30W
XL=wL=90W
The instantaneous voltage across
each element is the PROJECTION
of the MAXIIMUM voltage onto
the horizontal axis!
This is the SAME as the sum of the
maximum vectors projected onto
the horizontal axis. I wt

13. I wt Source voltage leads the current by the angle f. w=3 KHZ R=30 W
L= 30 mH
w=3 KHZ

14. I wt The drawing is obviously NOT to scale. w=3 KHZ R=30 W E=60V
L= 30 mH
w=3 KHZ wt

16. 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,

17. capacitor phasor diagram

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

19. SUMMARY

20. An AC source with ΔVmax = 125 V and f = 25
An AC source with ΔVmax = 125 V and f = 25.0 Hz is connected between points a and d in the figure.
Calculate the maximum voltages between the following points: (a) a and b V (b) b and c V (c) c and d V (d) b and d V

21. ac circuits look complicated