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Es Martinez
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Warren
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2. AC Circuits & Phasors

3. Which phasor shows a current that is positive and increasing? D
Which phasor shows a current that is negative with an increasing magnitude (i.e. getting more negative?) B

4. X = “reactance”; the effective combination of Xs in a circuit is called “impedance.”

5. At high frequencies, the reactance of what circuit element decreases
At high frequencies, the reactance of what circuit element decreases? A] resistor B] capacitor C] inductor D] none decrease E] all decrease
Low reactance is like low resistance… small voltage drop for a large current.

9. An AC voltage source drives a sinusoidal current through two resistors.
The amplitude of the sinusoidal voltage across the top resistor is 4 V.
The amplitude of the sinusoidal voltage across the bottom resistor is 3 V.
What is the amplitude of the sinusoidal voltage provided by the source?
A] 0 V D] 7 V
B] 1 V E] 12 V
C] 5 V

10. An AC voltage source drives a sinusoidal current through a resistor and an inductor in series.
The amplitude of the sinusoidal voltage across the top resistor is 4 V.
The amplitude of the sinusoidal voltage across the bottom inductor is 3 V.
What is the amplitude of the sinusoidal voltage provided by the source?
A] 0 V D] 7 V
B] 1 V E] 12 V
C] 5 V

11. An AC voltage source drives a sinusoidal current through a capacitor and a resistor in series.
The amplitude of the sinusoidal voltage across the top capacitor is 4 V.
The amplitude of the sinusoidal voltage across the bottom resistor is 3 V.
What is the amplitude of the sinusoidal voltage provided by the source?
A] 0 V D] 7 V
B] 1 V E] 12 V
C] 5 V

12. An AC voltage source drives a sinusoidal current through a capacitor and an inductor in series.
The amplitude of the sinusoidal voltage across the top capacitor is 4 V.
The amplitude of the sinusoidal voltage across the bottom inductor is 3 V.
What is the amplitude of the sinusoidal voltage provided by the source?
A] 0 V D] 7 V
B] 1 V E] 12 V
C] 5 V

16. Ampere’s law
This completes
“Maxwell’s Equations” 16

17. Electromagnetic “Discontinuities” Must Propagate at a speed

19. Our wavefront
satisfies both “Gauss’s laws”
because there is no
enclosed charge or current, and fields on opposite sides of the box are the same.

20. There is a changing B flux as the wavefront moves by
There is a changing B flux as the wavefront moves by. This changing flux must be equal to the line integral of the E field. Only the back edge (gh) contributes to this line integral.

21. There is a changing E flux also
There is a changing E flux also. This gives another reqd relation between E and B.

22. Accelerating Charges Radiate http://www. its. caltech

23. Accelerating Charges Radiate

24. Coulomb’s law can’t describe the “kinked” E field
Coulomb’s law can’t describe the “kinked” E field. We got it from connecting field lines (Gauss’ law!) + geometry. So, while Gauss “derived” his law from Coulomb, Gauss’ Law is better. It’s always true, while Coulomb’s law is only true for unaccelerated charges.

25. But what’s it good for?
2:33

26. Quiz: What are you doing over break (2 pts for any answer):
A] Maybe a physics problem a week or so, just to stay in top mental condition
B] I won’t pick up a physics book
C] I will use my expertise from Physics 161 to re-animate dead tissue.
All answers got 2 points, but C is of course the best answer.