Lecture 19 1 Potential Difference Across Inductor V

Lecture 19 -1 Potential Difference Across Inductor + V internal resistance I • Analogous to a battery • An ideal inductor has r=0 - • All dissipative effects are to be included in the internal resistance (i. e. , those of the iron core if any)

Lecture 19 -2 Ways to Change Magnetic Flux • Changing the magnitude of the field within a conducting loop (or coil). • Changing the area of the loop (or coil) that lies within the magnetic field. • Changing the relative orientation of the field and the loop. motor generator http: //www. wvic. com/how-gen-works. htm

Lecture 19 -3 Alternating Current (AC) = Electric current that changes direction periodically ac generator is a device which creates an ac emf/current. A sinusoidally oscillating EMF is induced in a loop of wire that rotates in a uniform magnetic field. where ac motor = ac generator run in reverse http: //www. wvic. com/how-gen-works. htm http: //www. pbs. org/wgbh/amex/edison/sfeature/acdc. html

Lecture 19 -4 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. + -- I(t) Kirchhoff’s Loop Rule: Ipeak v. R(t) and I(t) in phase

Lecture 19 -5 City lights viewed in a motion blurred exposure. The AC blinking causes the lines to be dotted rather than continuous (quote from Wikipedia)

Lecture 19 -6 Power Dissipated by Resistive Load VR and I in phase Power:

Lecture 19 -7 Average Power but

Lecture 19 -8 Similarly, Root-Mean-Square Values

Lecture 19 -9 Non-scored Test Quiz Which of the following statement is true? A. B. C. D.

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

Lecture 19 -11 Inductive Load Kirchhoff’s Loop Rule: v. L(t) leads I(t) by 90 (1/4 cycle) Power: + --

Lecture 19 -12 Capacitive vs Inductive Load I(t) leads v(t) by 90 capacitive reactance -- + v. L(t) leads I(t) by 90 inductive reactance + --

Lecture 19 -13 (Ideal) LC Circuit • From Kirchhoff’s Loop Rule • From Energy Conservation same harmonic oscillator with angular frequency Natural Frequency

Lecture 19 -14 LC Oscillations No Resistance = No dissipation

Lecture 19 -15 Physics 241 –Quiz 16 b – March 20, 2008 In most of Europe, the peak voltage of household outlets is 311 V. What is the rms voltage? a) 110 V b) 141 V c) 156 V d) 220 V e) 311 V

Lecture 19 -16 Physics 241 –Quiz 16 c – March 20, 2008 In Japan, the rms voltage of household outlets is 100 V. What is the peak voltage? a) 200 V b) 141 V c) 100 V d) 50 V e) 71 V