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Review of AC-circuit

Keys to deal with R, L, and C in an AC-circuit. Across R, voltage and current are in-phase Across L, the current lags behind voltage by 90 o Across C, the current leads voltage by 90 o. Review of AC-circuit. Also, . When two elements are in series  the same current passing through them

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Review of AC-circuit

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  1. Keys to deal with R, L, and C in an AC-circuit • Across R, voltage and current are in-phase • Across L, the current lags behind voltage by 90o • Across C, the current leads voltage by 90o Review of AC-circuit Also, • When two elements are in series  the same current passing through them • When two elements are in parallel  the same voltage across them

  2. Basics I and V are in-phase R I lags V by 90 degree L I leads V by 90 degree C

  3. RLC in series Key: IR, IL, and IC are all in phase DVR ~ R DVL ~ XL DVC ~ XC DVmax ~ Z

  4. Imax IC How do you draw the phasor diagram? IR = IL DVR What if RLC are not in series? Which of the following is true (a) DVc = DVL, IC = IL (b) DVc = DVL, IR = IL (c) DVc = DVR, IR = IL (d) DVL = DVR, IR = IL (e) DVc = DVL+ DVR, IC = IL (f) DVc = DVL+ DVR, IR = IL DVL DVc = DVR+ DVL

  5. Power dissipation • Only R dissipates power P = I *DV, always For L and C, I and DV are 90o out of phase  PL = 0, PC = 0 For R, I and DV are in-phase  PR = IDV = Irms2R

  6. PR = IDV = Irms2R Where Irms = Vrms/Z i.e. Resonance in RLC circuit in series For a fixed AC voltage source, maximum power dissipation occurs when XL = XC, ie. When Z = R

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