31. Alternating Current

What's the impedance of a parallel RC AC circuit?

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?

(II) An inductance coil operates at 240 V (rms) and 60.0 Hz. It draws 10.8 A (rms). What is the coil’s inductance?

What is the reactance of an 8.4-μF capacitor at a frequency of (a) 60.0 Hz, (b) 1.00 MHz?

(II) What is the inductance L of the primary of a transformer whose input is 110 V rms at 60.0 Hz and the rms current drawn is 3.8 A? Assume no current in the secondary.

(I) A 10.0-k Ω resistor is in series with a 34.0-mH inductor and an ac source. Calculate the impedance of the circuit if the source frequency is (a) 55.0 Hz; (b) 55.0 kHz.

(II) For a 120-V, 60-Hz voltage, a current of 70 mA passing through the body for 1.0 s could be lethal. What must be the impedance of the body for this to occur?

(II) The output of an electrocardiogram amplifier has an impedance of 45 Ω. It is to be connected to an 8.0-Ω loudspeaker through a transformer. What should be the turns ratio of the transformer?

(II) A 1.50-k Ω resistor in series with a 370-mH inductor is driven by an ac power supply. At what frequency is the impedance double that of the impedance at 60.0 Hz?

(II) A capacitor is placed in parallel with some device, B, as in Fig. 30–18b, to filter out stray high-frequency signals, but to allow ordinary 60.0-Hz ac to pass through with little loss. Suppose that circuit B in Fig. 30–18b is a resistance R = 530 Ω connected to ground, and that C = 0.35 μF. Calculate the ratio of the capacitor’s current amplitude to the incoming current’s amplitude if the incoming current has a frequency of (a) 60.0 Hz; (b) 60.0 kHz.

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