Concept #1: Impedance in AC Circuits

Example #1: Impedance of a Parallel LR AC Circuit

Practice: What’s the impedance of a parallel RC AC circuit?

Practice: An AC source operates at a maximum voltage of 120 V and an angular frequency of 377 s^{-1} . If this source is connected in parallel to a 15 Ω resistor and in parallel to a 0.20 mF capacitor, answer the following questions:

a) What is the maximum current produced by the source?

b) What is the maximum current through the resistor?

c) What is the maximum current through the capacitor?

A series ac circuit has a source with voltage amplitude V = 120 V and angular frequency ω = 50 rad/s, a resistor with R = 15 Ω and an inductor with L = 0.40 H. What is the current amplitude?

Consider the ac circuit shown in the sketch. R = 150 Ω and C = 5.0 x 10 -6 F. The source voltage amplitude is 800 V and the current amplitude is 2.0 A.
What is the amplitude of the voltage across the capacitor?

Consider the ac circuit shown in the sketch. R = 150 Ω and C = 5.0 x 10 -6 F. The source voltage amplitude is 800 V and the current amplitude is 2.0 A.
What is the angular frequency ω of the source?

Consider the ac circuit shown in the sketch. R = 150 Ω and C = 5.0 x 10 -6 F. The source voltage amplitude is 800 V and the current amplitude is 2.0 A.
What is the rate at which the source is supplying the electrical energy to the circuit?

In the circuit shown, the light bulb has a resistance R, and the ac emf drives the circuit with a frequency Z. Assuming that the brightness of a bulb is proportional to the power dissipated, which of the following statements is correct?A. The light bulb glows most brightly at very low frequencies.B. The light bulb does not glow at any frequency because AC current cannot flow through the bulb due to the presence of the capacitor.C. The light bulb glows most brightly at very high frequencies.D. The light bulb glows with the same brightness at all frequencies.E. The light bulb glows most brightly at the frequency ω = 1 / √LC

An ac series circuit contains a source with voltage amplitude V = 240 V and angular frequency ω = 100 rad/s. The circuit contains a resistor with R = 400 Ω and a capacitor with C = 5.0 x 10-5 F. What is the maximum voltage across the capacitor?

A series RLC circuit with L = 25 mH, C = 0.8 μF and R = 7Ω is driven by a generator with a maximum emf of 12V and a variable angular frequency ω. At ω = 8000 rad/sec the impedance Z of the circuit is:a) Z = 7 Ωb) Z = 12.3 Ωc) Z = 27.1 Ωd) Z = 44.3 Ωe) Z = 172 Ω

In an R-L-C ac series circuit the voltage across the capacitor is 64 V and the voltage amplitude across the inductor is 96 V. Does the source voltage lag or lead the current in the circuit?(a) lag(b) lead

The circuit shown in the sketch has an ac voltage source, a resistor and a capacitor connected in series. There is no inductor. the ac voltage source has voltage amplitude 900 V and angular frequency 20 rad/s. The voltage amplitude across the capacitor is 500 V. The resistor has resistance R = 300 Ω.Does the source voltage lag or lead the current?

A 60 Hz AC source with an rms voltage of 120 V is connected to a 50 Ω resistor and 30 μF capacitor in series.
(a) What is the impedance of this circuit?
(b) What is the maximum current output by the source?
(c) What is the maximum voltage accross the capacitor?