Summary

• Inductors
• Energy in magnetic fields
• LR and LC circuits

Today's joke


• Written quiz Ch. 30




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Chapter 32

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• AC circuits
• AC voltages
  ε = ε₀ cos wt
• rms voltage

Example #1

• The phasor
• rotating vectors
• projection on y-axis

Example #2

Example #3

• adding phasors



• Simple Circuits
• Interactive circuit applet
• Purely resistive, animated applet
• Purely capacitive, animated applet
• Purely inductive, animated applet

HRW10e 31.54
What is the maximum value of an ac voltage whose rms value is 100 V?

A. 70.7 V
B. 100 V
C. 141 V
D. 200 V
Answer



















Knight2 36.stt.01
The magnitude of the instantaneous value of the emf represented by this phasor is _____.

A. increasing
B. decreasing
C. constant
D. [Not enough information to answer]
Answer



















PoP5 QQ 33.1mod
For which of the depicted phasors is the magnitude of the instantaneous value of the voltage increasing?

A. (a) only
B. (b) only
C. (c) only
D. (a) and (b)
E. (b) and (c)
F. (a), (b), and (c)
Answer



























 



C. 141 V




















 



A. increasing
The phasor rotates counterclockwise. As it approaches the negative y axis, the projection of ε₀ onto the y axis is increasing, and that represents the instantaneously measured value of the emf. The magnitude of the emf is increasing, but its value is becoming more negative as it approaches −ε₀.



















 



E. (b) and (c)

The phasor rotates counterclockwise. As it approaches the positive x axis in (a), the projection of ΔV_max onto the y axis is decreasing, and that represents the instantaneously measured value of the voltage. For each of phasors (b) and (c) the projection of ΔV_max onto the y axis is increasing.



























This cartoon caption was written by the famous movie critic Roger Ebert. It was not a winning entry, but I like it. I saw the cartoon in an online article after his death. And here is a blog written by Mr. Ebert about his cartoon writing efforts.