21-13 LRC series AC Circuit; Problem Solving

•We analyze an LRC circuit by using a phasor diagram….an xy coordinate system….arrows acting like vectors…(not real…but, phasors)…the length of each arrow represents the magnitude of the peak voltage across each element:•Vro =I0 R VLO =I0 XL VCO =I0 XC

•See page 647• Using this diagram, we can determine

the total impedance Z of the circuit. (See formulas p 647)•See Example 21-156

•Cos= the power factor

21-14 Resonance in AC Circuits; Oscillators

• See formulas page 649.• See diagrams page 649• Resonant frequency f0 = (1/2)( )•

When R is very small, we can refer to LRC as an LC circuit.

• The energy in an LC circuit oscillates, at frequency, between the inductor and the capacitor , with some being dissipated in R.

• See page 649

LC/1

• This process of the charge flowing back and forth from one plate of the capacitor to the other, through the inductor, continues to repeat itself. This is called an LC oscillation or an electromagnetic oscillation.

• LC circuits are used in oscillators.

21-15 Impedance Matching

• Often, two circuits are attached and they must be matched to the same impedance.

• Maximum power is transmitted between two circuits, when the output impedance of one matches the input impedance of the second circuit.

• See page 651