Concept #1: Power in AC Circuits

Consider the AC circuit in which a capacitor and a lightbulb are connected in series with the AC source. The frequency of the AC source is adjusted while its voltage amplitude is held constant. The lightbulb will glow the brightest at which of the following?
A) same at all frequencies
B) high frequencies
C) low frequencies
D) zero frequency (DC)

The following graph gives the current and emf voltages as a function of time for a driven, series LRC circuit. To increase the average power delivered by the source, which of the folowing parameters should be increased?
A) Driving frequency
B) Resistance
C) Inductance
D) Increasing any of the above will decrease the average power delivered by the source

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. If the inductance L is doubled (keeping all other quantities given, including the generator frequency, the same), compared to the power dissipated when the circuit was at resonance, the power now dissipated in the resistor willa) increase.b) decrease.c) stay the same.

In the circuit shown below, the AC generator supplies an EMF of the form ε = 15sin (100t - π/3) volts. A student measures the current to be I = 6 sin(100t) amps. Thus, the generator voltage lags the current by π/3 radian (i.e. 60°). The average power delivered by the AC generator is:a. 22.5 Wb. 45.0 Wc. 39.0 W

A series circuit consists of a 15-Ω resistor, a 25-mH inductor, and a 35-μF capacitor. If the frequency is 100 Hz the power factor is:A. 0.89B. 0C. 1.0D. 0.20E. 0.45