Chapter 21 Notes College Physics by Giambattista et al. Basic AC ...

Chapter 21 NotesCollege Physics by Giambattista et al.Basic AC CircuitsINPUT ac voltage E(t) = E m sin ωtOUTPUT ac current i(t) = I m sin (ωt – φ)E(t)E m0 tT 2T–E mHow does the current compare with the driving voltage (emf)?Peak is reduced by Ohm’s Law for ac circuits:I = E/ZWaveform is shifted by a phase angle φ: –90° ≤ φ ≤ +90°Root-Mean-Square Value a type of average related to standard deviationpeakrms 2 Ohm’s Law: V rms = I rms Z or V m = I m ZPower Law: P av = I 2 rmsR or P av = ½ I 2 mRComponents of Basic AC Circuits:1) Resistors – cause heat to dissipate but do not introduce a phase shift2) Capacitors – store charge, impede low frequencies, adds (–) phase shift3) Inductors – store current, impede high frequencies, add (+) phase shiftInductors are coils, rated by their inductance L, SI unit: henry (H)IMPEDANCE ZRESISTANCE RREACTANCE XCAPACITIVE X CINDUCTIVE X L L1X C C 2fX LOhm’s Law: V R = IR V C = IX C V L = IX LJohn B. Ross, Ph.D.IUPUI Physics Dept.

Chapter 21 NotesCollege Physics by Giambattista et al.Phase Diagram: X L +90°R 0°X C –90°Resonancephenomenon found in a variety of physical systemsdiscuss pumping legs on swing, cracking glass with sound, musical instruments,Tacoma Narrows Bridge in Wash.What happens when the driving frequency equals ω 0 ?Maximum currentMinimum total impedanceCurrent in phase with driving voltageMaximum power transferred from source to circuitX L = X C 0 1LCJohn B. Ross, Ph.D.IUPUI Physics Dept.