ADV/TEC 3: Introducing Capacitors and Inductors - PowerPoint PPT Presentation

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ADV/TEC 3: Introducing Capacitors and Inductors PowerPoint Presentation
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ADV/TEC 3: Introducing Capacitors and Inductors

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  1. ADV/TEC 3: Introducing Capacitors and Inductors Introductory mini-lecture

  2. Capacitors • A capacitor is any two conductors separated by an insulator • Voltage across a capacitor is proportional to the charge on each plate, q = Cv

  3. Capacitors • Apply voltage v = V0ejωt • Charge builds up on plates, q = C V0 ejωt • A change in voltage drives electrons from one plate to the other around the circuit, producing a current • j indicates a 90o phase difference between i & v i.e., v ‘lags’ i by 90o (or π/2) • Impedance Z = v/i= 1/jωC, Reactance XC = -1/ωC

  4. Capacitors Currentleadsvoltage

  5. Inductors • An inductor is a coil of wire usually wound on a magnetic core • Current through the coil produces a magnetic field proportional to the current • As the current changes the magnetic field changes, inducing a voltage that opposes the change in current (by Lenz’s law)

  6. Inductors • If we apply an alternating voltage v = V0e jωt, then integration gives • The j indicates a 90o phase difference between i& v i.e., v ‘leads’ i by 90o • Impedance Z = v/i= jωL, Reactance XL = ωL

  7. Inductors Voltage leads current

  8. Real Inductors • Real inductors have resistance, RL, so the impedance is • Ohm’s Law then becomes: i.e., applied voltage v is the vector sum of vL and vR • Phase angle: