31. Alternating Current
Resistors in AC Circuits
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- Multiple Choice
The voltage across a resistor is found to be given by v R (t) = (10 V) cos[(120 s−1)t]:
a) At what frequency does the AC course operate?
b) If the resistance is 12 Ω, what is the maximum current in this circuit?
c) What is the RMS voltage of the AC source?
682views7rank - Multiple ChoiceIn a kitchen in the United States, you turn on a toaster, a microwave, and a coffee machine at the same time. All are wired in parallel and are connected to a 20A circuit breaker. If the toaster uses and the coffee machine uses what is the maximum power the microwave could use without tripping the circuit breaker?487views
- Textbook Question
Calculate the peak current in a 2.5-k Ω resistor connected to a 220-V rms ac source.
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Estimate the resistance of the 120-Vrms circuits in your house as seen by the power company, when everything electrical is unplugged.
288views - Textbook Question
A high-pass RC filter with a crossover frequency of 1000 Hz uses a 100 Ω resistor. What is the value of the capacitor?
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In a plasma globe, a hollow glass sphere is filled with low-pressure gas and a small spherical metal electrode is located at its center. Assume an ac voltage source of peak voltage Vo and frequency f is applied between the metal sphere and the ground, and that a person is touching the outer surface of the globe with a fingertip, whose approximate area is 1.0 cm². The equivalent circuit for this situation is shown in Fig. 30–36, where RG and RP are the resistances of the gas and the person, respectively, and C is the capacitance formed by the gas, glass, and finger. (a) Determine C assuming it is a parallel-plate capacitor. The conductive gas and the person’s fingertip form the opposing plates of area A = 1.0 cm². The plates are separated by glass (dielectric constant K = 5.0) of thickness d = 2.0 mm. (b) In a typical plasma globe, f = 12 kHz. Determine the reactance XC of C at this frequency in MΩ. (c) The voltage may be Vo = 2500 V. With this high voltage, the dielectric strength of the gas is exceeded and the gas becomes ionized. In this “plasma” state, the gas emits light (“sparks”) and is highly conductive so that RG << XC. Assuming also that RP << XC, estimate the peak current that flows in the given circuit. Is this level of current dangerous? (d) If the plasma globe operated at f = 1.0 MHz, estimate the peak current that would flow in the given circuit. Is this level of current dangerous?
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