1. Lecture 11 Electromagnetic Oscillations and Alternating Current Ch. 31
Topics
Transformers
LC Circuit Qualitatively
Electrical and Magnetic energy oscillations
Alternating current
Pure R and L circuits
Series RLC circuit
Power and Transformers
Demos
Elmo
Polling

2. Quiz 2 Resistivity and currents Apply Kirchhoff Laws to circuits
B fields from simple current geometries
Faraday’s and Lenz’s Law. Electric fields from changing B fields
Find acceleration and velocity of partikcles in E and B fields
RL circuits

3. What is a Generator? Coil of wire Where w is the rotational angular B
Where w is the rotational angular
frequency of the generator
w= 2pf and f= 60 Hz

20. Driven RLC Series Circuit

28. Series RLC Show Generator voltage vs time on scope. Vary frequency
Show voltage across resistor compared to signal voltage
How is signal voltage related to voltage across resistor
Vary frequency - ELI the ICE man
Show voltage across inductor compared to resistor.
Voltage across resistor is in phase with current through resistor
Does voltage across inductor lead or lag the current
Show voltage across capacitor compared to resistor.
Does voltage across the capacitor lead or lag the current
Show phase angle is related to impedance in circuit and is
frequency dependent
Show resonance by varying frequency.
Need table of numbers for some frequency and at resonance.

30. Series LCR circuit

31.  f Hz 6.28fL 4.2mH 1/6.28fC 1uF R Ohms Z I=V/Z Amps Deg VR VoltsVL VC
100
2.7
1600 10 40
0.25
-89.6
.05
1000 27
160
133
0.075
-85.7
.25 1
2445
65.3
9.0 20
-20
10000
270 16
0.037
87.7
0.2
0.6

33. Peak value
Effective Power
rms=root-mean-square

36. Low Pass Filter
High Pass Filter

40. Chapter 13 Problem 17
In an oscillating LC circuit, L = 28.0 mH and C = 7.50 µF. At time t = 0 the current is 9.50 mA, the charge on the capacitor is 3.20 µC, and the capacitor is charging.
(a) What is the total energy in the circuit?
(b) What is the maximum charge on the capacitor?
(c) What is the maximum current?
(d) If the charge on the capacitor is given by q = Q cos(ωt + ϕ), what is the phase angle ϕ?
(e) Suppose the data are the same, except that the capacitor is discharging at t = 0. What then is ϕ?

41. Chapter 31 Problem 21
In an oscillating LC circuit with C = 62.0 µF, the current as a function of time is given by I = (1.10) sin(2500t ), where t is in seconds, I in amperes, and the phase angle in radians.
(a) How soon after t = 0 will the current reach its maximum value?
(b) What is the inductance L?
(c) What is the total energy?