Physics 222 supplemental instruction

Class 21 RLC and AC Circuits November 1st, 2017

1. Which one of the phasor diagrams shown below best represents a series LRC circuit driven at resonance?

2. An AC circuit is shown in the figure. The rms current in the circuit is 1.3 A. What is the peak magnetic energy in the inductor?

A. 0.64 JB. 0.80 JC. 0.16 JD. 0.32 JE. 0.48 J

3. In a series LRC circuit, the frequency at which the circuit is at resonance if f0. If you double the resistance, the inductance, the capacitance, and the voltage amplitude of the AC source, what is the new resonance frequency?

A. 4f0B. f0/4C. 2f0D. f0/2E. f0

4. In the LC circuit shown in the figure, the switch is initially open and a charge of 1.0 C is put on the capacitor. The switch is then closed at time t = 0 s. When does the magnitude of the charge on the capacitor first return to its original value?

A. At t = 1.0 sB. At t = 0.5 sC. At t = 3.1 sD. At t = 6.3 sE. None of the above.

5. In the circuit, the switch has been at “a” for a long time. Then it is moved to “b”. What is the angular frequency of of the charge oscillations? What is the maximum energy stored in the inductor?

A. 0.25 s-1

B. 0.5 s-1

C. 50 s-1

D. 500 s-1

E. 2.5 x 10-8 s-1

A. 10 mJB. 30 mJC. 50 mJD. 100 mJE. 150 mJ