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

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

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

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

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?

the phasor

direction wt wt

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.

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

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

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

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

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

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,

capacitor phasor diagram

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

SUMMARY

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 62.8 V (b) b and c 45.6 V (c) c and d 154 V (d) b and d 108 V

ac circuits look complicated http://www.ngsir.netfirms.com/englishhtm/RLC.htm