Fig 33-CO, p.1033

Ch 33 Alternating Current Circuits

33.1 AC Sources and Phasors

v = Vmaxsint = 2/T = 2f

t

Vmaxv = Vmaxsint

Phasor

CT1: The phasor diagrams below represent three oscillating voltages having different amplitudes and frequencies at a certain instant of time t = 0. As t increases, each phasor rotates counterclockwise and completely determines a sinusoidal oscillation. At the instant of time shown, the instantaneous value of v associated with each phasor is given in ascending order by diagrams

A. a,b,c.B. a,c,b.C. b,c,a.D. b,a,c.E. c,a,bF. c,b,a

CT2: Consider the pairs of phasors below, each shown at t = 0. All are characterized by a common frequency of oscillation . If we add the oscillations, the maximum amplitude is achieved for pair(s)

A. a.B. b.C. c.D. d.E. e.F. c and d.G. a and c.H. b and c.

Ch 33 Alternating Current Circuits

33.2 Resistors in an AC Circuit

iR = vR/R = Vmaxsint/R = Imaxsint

Imax = Vmax/R

Ch 33 Alternating Current Circuits

33.2 Resistors in an AC Circuit

Irms = Imax/21/2 Vrms = Vmax/21/2

Pav = Prms = Irms2R = Vrms

2/R

Vrms = IrmsR

P33.2 (p.946)

P33.4 (p.946)

Ch 33 Alternating Current Circuits

33.3 Inductors in an AC Circuit

vL = Vmaxsint Imax = Vmax/L

iL = Imaxsin(t - /2) lags voltage by /2

P33.11 (p.946) XL = L Imax = Vmax/XL

Ch 33 Alternating Current Circuits

33.4 Capacitors in an AC Circuit

vL = Vmaxsint Imax = CVmax

iC = Imaxsin(t + /2) leads voltage by /2

P33.15 (p.946) XC = 1/C Imax = Vmax/XC

CT3: The light bulb has a resistance R, and theemf drives the circuit with a frequency .The light bulb glows most brightly at

A. very low frequencies.B. very high frequencies.C. the frequency = (1/LC)1/2

Fig 33-14, p.1044

Ch 33 Alternating Current Circuits

33.5 RLC Series Circuit

v = Vmaxsint Imax = Vmax/Z

i = Imaxsin(t - ) I lags voltage by

Z = (R2 + (XL – XC)2)1/2 = tan-1[(XL –XC)/R]

i

P33.17 (p.946)

P33.27 (p.947)

Ch 33 Alternating Current Circuits

33.6 Power in an AC Circuit

Pav = Prms = IrmsVrmscos

cos is called the power factor

Check P33.27 (p.947)

i

Ch 33 Alternating Current Circuits

33.7 Resonance in a Series RLC Circuit

Pav = Vrms2R/(R2 + L2(2 - 0

2)2/2)

0 = (1/LC)1/2 Q = 0/ = R/L

i

CT4: For the RLC series circuit shown, which ofthese statements is/are true:(i) Potential energy oscillates between C and L.(ii) The source does no net work: Energy lostin R is compensated by energy stored in C and L.(iii) The current through C is 90° out of phasewith the current through L.(iv) The current through C is 180° out of phasewith the current through L.(v) All energy is dissipated in R.

A. all of themB. none of themC. (v) D. (ii)E. (i), (iv), and (v)F. (i) and (v)G. none of the above

P33.38 (p.948)

Ch 33 Alternating Current Circuits

33.8 The Transformer and Power Transmission

V2 = N2V1/N1

Ideal Transformer: Ppri = I1V1 = Psec = I2V2

P33.41 (p.948)

i

V2

CT5: When the switch is closed, the potential difference across R is

A. V(N2 /N1).B. V(N1/N2).C. V.D. zero.E. insufficient information

CT6: The primary coil of a transformer is connected to a battery, a resistor, and a switch. The secondary coil is connected to an ammeter. When the switch is thrown closed, the ammeter shows

A. zero current.B. a nonzero current for a short instant.C. a steady current.