Problem 71
The field coils used in an ac motor are designed to have a resistance of $0.45
\Omega\( and an impedance of \)35.0 \Omega$ What inductance is required if the
frequency of the ac source is (a) \(60.0 \mathrm{Hz} ?\) and (b) $0.20
\mathrm{kHz} ?$
Problem 72
A capacitor is rated at \(0.025 \mu \mathrm{F}\). How much rms current flows
when the capacitor is connected to a \(110-\mathrm{V}\) rms, \(60.0-\mathrm{Hz}\)
line?
Problem 73
A capacitor to be used in a radio is to have a reactance of \(6.20 \Omega\) at a
frequency of \(520 \mathrm{Hz}\). What is the capacitance?
Problem 74
An alternator supplics a peak current of \(4.68 \mathrm{A}\) to a coil with a
negligibly small internal resistance. The voltage of the alternator is
\(420-\mathrm{V}\) peak at \(60.0 \mathrm{Hz}\) When a capacitor of $38.0 \mu
\mathrm{F}$ is placed in series with the coil, the power factor is found to be
\(1.00 .\) Find
(a) the inductive reactance of the coil and (b) the inductance of the coil.
Problem 75
At what frequency does the maximum current flow through a series RLC circuit
containing a resistance of \(4.50 \Omega,\) an inductance of \(440 \mathrm{mH},\)
and a capacitance of
\(520 \mathrm{pF} ?\)
Problem 76
What is the rins current flowing in a \(4.50-\mathrm{kW}\) motor connected to a
\(220-\mathrm{V}\) rms line when (a) the power factor is 1.00 and (b) when it is
\(0.80 ?\)
Problem 77
A variable capacitor is connected in series to an inductor with negligible
internal resistance and of inductance \(2.4 \times 10^{-4} \mathrm{H} .\) The
combination is used as a tuner for a radio. If the lowest frequency to be
tuned in is \(0.52 \mathrm{MHz}\). what is the maximum capacitance required?
Problem 78
A large coil used as an electromagnet has a resistance of \(R=450 \Omega\) and
an inductance of \(L=2.47 \mathrm{H} .\) The coil is connected to an ac source
with a voltage amplitude of \(2.0 \mathrm{kV}\) and a frequency of $9.55
\mathrm{Hz}$. (a) What is the power factor? (b) What is the impedance of the
circuit? (c) What is the peak current in the circuit? (d) What is the average
power delivered to the electromagnet by the source?
Problem 79
An ac series circuit containing a capacitor, inductor, and resistance is found
to have a current of amplitude \(0.50 \mathrm{A}\) for a source voltage of
amplitude \(10.0 \mathrm{V}\) at an angular frequency of $200.0 \mathrm{rad} /
\mathrm{s} .\( The total resistance in the circuit is \)15.0 \Omega$ (a) What
are the power factor and the phase angle for the circuit? (b) Can you
determine whether the current leads or lags the source voltage? Explain.
Problem 80
A generator supplies an average power of \(12 \mathrm{MW}\) through a
transmission line that has a resistance of \(10.0 \Omega .\) What is the power
loss in the transmission line if the rms line voltage \(8_{\text {rms }}\) is
(a) \(15 \mathrm{kV}\) and (b) \(110 \mathrm{kV} ?\) What percentage of the total
power supplied by the generator is lost in the transmission line in each case?
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