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

2.  B Where  is the rotational angular frequency of the generator  f and f= 60 Hz Coil of wire What is a Generator?

19. Driven RLC Series Circuit

27. 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. Voltage across resistor is in phase with current through 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.

29. Series LCR circuit

30. f Hz ωL Ohms 1/ωC Ohms R Ohms Z Ohms I=V/Z Amps  Deg V R Volt s VLVL VCVC 1002.716001016000.006-89.6.06.01 6 9.6 100027160101330.075-85.7.752.012 244565.3 10 10 65. 3 1000027016102700.03787.70.37100.6 V=10 Volts

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

35. Low Pass Filter High Pass Filter

39. 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 ?

40. 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 + 0.670), 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?