Lecture 29 - AC circuits. Phasors

# Lecture 29 - AC circuits. Phasors - Driven RLC circuit...

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1 Lecture 29 AC circuits Phasors AC circuits. Phasors. Driven RLC circuit Analogy between circuits and SHM: Circuits Mechanical Oscillations. LC Si/ ( S H M No energy dissipation. Spring/mass (SHM) Oscillations with decreasing amplitude. Energy dissipation. RLC Spring/mass with damping Driven oscillations. Energy dissipation and supply RLC with AC generator Spring/mass with damping and driving force Preview Source : produces an oscillating voltage (supplies whatever current the rest of the circuit “requires”) Resistor : causes a voltage drop when a current flows through As soon as the voltage changes so does the ~ through. As soon as the voltage changes, so does the current always in phase . Capacitor : resists change in charge Q resists change in voltage. Voltage across capacitor lags behind the current by 90°. Inductor : resists change in magnetic flux resists change in current. Voltage across inductor is ahead of the current by 90 ˚ . AC generator Generic problem: we are given an AC voltage source that “drives” a circuit Supplies a given emf that depends on time (usually as a sine of cosine cos Et sine of cosine) Goal: Determine current that flows:  cos iI t  Current must be the same through all elements if they are in series.

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Lecture 29 - AC circuits. Phasors - Driven RLC circuit...

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