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Series R-L-C AC circuits Most complex we will consider ∆V = ∆Vgenerator Fig. 21-8, p.699 Voltage across each element still obeys Ohm-like law: ∆VR ,max = I max R ∆VL ,max = I max X L = ∆VC ,max = I max X C = What is the same for all three elements? But their voltage peaks (maximums) occur VL and VC are always VR is always _________ period shifted from VL and VC Phase difference between I and V Impedance Z is reactance of L, R C together Z= R 2 2 + (X L − X C ) X L − XC R φ = tan −1 ∆Vgenerator ,max = Average power delivered to circuit Speaker impedance matching Fig. 21-8, p.699 Where does it go? 4Ω 8Ω 30−60Ω Pav = I rms ∆Vgenerator ,rms cos φ = = I rmsVR ,rms = I rms R = 2 Power needed for headphones? VR ,rms 2 R In an LRC circuit, at a certain frequency X L = 3Ω, X c = 1Ω, and R = 1Ω. The generator voltage is ∆Vgenerator , rms = 10 volts LRC resonance Irms P1. The maximum voltage put out by the generator is ___ V (see rms vs max definition last time). __ A. 5 C. 14 E. 28 B. 10 D. 20 Frequency P2. The maximum current in the circuit is ___ A A. 2.5 C. 5.5 E. 8.5 B. 4.5 D. 6.5 P3. The average power delivered is ____ W A. 2 C. 6 E. 10 B. 4 D. 8 Current depends on frequency: biggest possible current occurs when Z is a minimum! Or can tune circuit to match a certain frequency! Variable capacitor P4. If the frequency is doubled the power A. increases B. decreases C. stays the same World’s simplest radio!