1. Lecture 19-1 RL Circuits – Starting Current 2. Loop Rule: 3. Solve this differential equation τ=L/R is the inductive time constant 1.Switch to e at t=0 As the current tries to begin flowing, self-inductance induces back EMF, thus opposing the increase of I. + - ε/R

2. Lecture 19-2 Alternating Current (AC) = Electric current that changes direction periodically ac generator is a device which creates an ac emf/current. ac motor = ac generator run in “reverse” A sinusoidally oscillating EMF is induced in a loop of wire that rotates in a uniform magnetic field. where

3. Lecture 19-3 ©2008 by W.H. Freeman and Company

4. Lecture 19-4 READING QUIZ 1 \ Which of the following statements is correct ? A| In A.C. circuit with a A.C. generator and an ideal capacitor the current lags the voltage. B| In an A.C. circuit with a A.C. generator and an ideal inductor the current leads the voltage. C| In an circuit consists of an ideal inductor and an ideal capacitor. The capacitor is initially charged. After the switch is thrown energy is dissipated every cycle. D| In an A.C. circuit consists of an ideal inductor, an ideal capacitor and a series resistor. Initially the capacitor is charged After the switch is thrown energy is dissipated.

5. Lecture 19-5 Resistive Load Start by considering simple circuits with one element (R, C, or L) in addition to the driving emf. Pick a resistor R first. v R (t) and I(t) in phase Kirchhoff’s Loop Rule: I peak + -- I(t)

6. Lecture 19-6 ©2008 by W.H. Freeman and Company

7. Lecture 19-7 Power Dissipated by Resistive Load V R and I in phase Power:

8. Lecture 19-8 Average Power but

9. Lecture 19-9 Root-Mean-Square Values Similarly,

10. Lecture 19-10 Capacitive Load I(t) leads v(t) by 90 o (1/4 cycle) Loop Rule: Power: +--

11. Lecture 19-11 ©2008 by W.H. Freeman and Company

12. Lecture 19-12 Inductive Load I(t) lags v(t) by 90 o (1/4 cycle) Kirchhoff’s Loop Rule: Power: +--

13. Lecture 19-13 ©2008 by W.H. Freeman and Company

14. Lecture 19-14 -- Capacitive vs Inductive Load I(t) leads v(t) by 90 o capacitive reactance + -- + v L (t) leads I(t) by 90 o inductive reactance vLvL

15. Lecture 19-15 WARM UP QUIZ 2 Which of the following statements is correct? A. B. C. D.

16. Lecture 19-16 ENERGY STORED IN AN INDUCTOR 6C07

17. Lecture 19-17 (Ideal) LC Circuit From Kirchhoff’s Loop Rule From Energy Conservation same Natural Frequency harmonic oscillator with angular frequency

18. Lecture 19-18 ©2008 by W.H. Freeman and Company

19. Lecture 19-19 RC Circuit vs LC Circuit RC +Q -Q I convention so that t I 0 -Q/(CR) t 0 -I max I max In RC circuit, current I causes energy dissipation in resistor R. exponential decay In LC circuit, there is no energy dissipation – energy can be stored in L, C, or both. sinusoidal oscillation

20. Lecture 19-20 ©2008 by W.H. Freeman and Company

21. Lecture 19-21 ©2008 by W.H. Freeman and Company

22. Lecture 19-22 DEMO DAMPED OSCILLATIONS 6C10

23. Lecture 19-23 LC Oscillations No Resistance = No dissipation

24. Lecture 19-24 PHYSICS 241 NOVEMBER 1, 2011 10:30 QUIZ 3 In most of Europe, the rms voltage of household outlets is 220V. What is the peak voltage? a) 110V b) 141V c) 156V d) 220V e) 311V

25. Lecture 19-25 PHYSICS 241 NOVEMBER 1, 2011 10:30 QUIZ 3 In most of Europe, the peak voltage of household outlets is 311V. What is the rms voltage? a) 110V b) 141V c) 156V d) 220V e) 311V

26. Lecture 19-26 PHYSICS 241 –MARCH 24, 2011 QUIZ 3 In Japan, the rms voltage of household outlets is 100V. What is the peak voltage? a) 200V b) 141V c) 100V d) 50V e) 71V