# AC & Capacitors Does Kirchoffs Voltage Law apply to AC Circuits? V R =6.0V V C = 8.0VV s = 10.0V.

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AC & Capacitors Does Kirchoffs Voltage Law apply to AC Circuits? V R =6.0V V C = 8.0VV s = 10.0V

AC & Capacitors Does Kirchoffs Voltage Law apply to AC Circuits? V R =6.0V V C = 8.0VV s = 10.0V YES! It DOES!!

Consider the graphs of the voltages of the components :

Consider the graphs of the 3 components voltages :

At Any Instant in time the Vs=Vr+Vc So Kirchhoffs Laws DO apply – its just that our voltages are out of phase with one another

Phase Relationship for Voltages in a R-L Circuit VRVR VCVC VCVC VRVR VSVS V R leads V c by º V C lags V S by (90- )º V S 2 = V c 2 + V R 2

Impedence (Z) The combined effect of resistance and reactance in a circuit. SI Unit: Ω V R =IR V C =IX c V s =IZSo Z 2 = R 2 + X c 2

Impedance Phasors can help us see the relationship for Impedance VCVC VRVR VSVS V S 2 = V C 2 + V R 2 V C = IX C V R = IR V S = IZ XCXC Z R Z 2 = X c 2 + R 2

Summary: Reactance: Voltage: Phase Difference: Impedance: V S 2 = V C 2 + V R 2 X C = 1/(2 ƒC) Z 2 = X C 2 + R 2 V R leads Vc

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