Review of AC-circuit
Keys to deal with R, L, and C in an AC-circuit
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•
•
Across R, voltage and current are in-phase
Across L, the current lags behind voltage by 90o , XL = wL
Across C, the current leads voltage by 90o , XC = 1/wC
Also,
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•
When two elements are in series  the same current
passing through them
When two elements are in parallel  the same voltage
across them
R
I and V are in-phase
C
I leads V by 90 degree
L
I lags V by 90 degree
RLC in series
Key: IR, IL, and IC are all in phase
DVR ~ R
DVL ~ XL
DVC ~ XC
DVmax ~ Z
Z  R2  ( X L  X C )2
 XL  XC 

R


  tan 1 
What if RLC are not in series?
Which of the following is true
(a) DVc = DVL, IC = IL
(b) DVc = DVL, IR = IL
(c) DVL = DVR, IR = IL
(d) DVc = DVL+ DVR, IC = IL
(e) DVc = DVL+ DVR, IR = IL
DVL
How do you draw the phasor diagram?
Imax
DVc = DVR+ DVL
IC
IR = IL
DVR
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