1. 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 When two elements are in series  the same current passing through them When two elements are in parallel  the same voltage across them Also,

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

3. RLC in series Key: I R, I L, and I C are all in phase  V L ~ X L  V C ~ X C  V R ~ R  V max ~ Z

4. What if RLC are not in series? Which of the following is true (a)  V c =  V L, I C = I L (b)  V c =  V L, I R = I L (c)  V c =  V R, I R = I L (d)  V L =  V R, I R = I L How do you draw the phasor diagram? VLVL VRVR I R = I L ICIC (e)  V c =  V L +  V R, I C = I L (f)  V c =  V L +  V R, I R = I L I max  V c =  V R +  V L

5. Power dissipation Only R dissipates power P = I *  V, always For L and C, I and  V are 90 o out of phase  P L = 0, P C = 0 For R, I and  V are in-phase  P R = I  V = I rms 2 R

6. Resonance in RLC circuit in series For a fixed AC voltage source, maximum power dissipation occurs when X L = X C, ie. When Z = R P R = I  V = I rms 2 R Where I rms = V rms /Z i.e.