Chapter 30: Problem 56
A \(35-\mathrm{mH}\) inductor with \(2.0-\Omega\) resistance is connected in series to a \(26-\mu \mathrm{F}\) capacitor and a \(60-\mathrm{Hz}, 45-\mathrm{V}(\mathrm{rms})\) source. Calculate \((a)\) the rms current, \((b)\) the phase angle, and \((c)\) the power dissipated in this circuit.
Short Answer
Expert verified
(a) 0.506 A, (b) -88.7°, (c) 0.513 W
Step by step solution
01
Calculate Inductive Reactance
The inductive reactance \(X_L\) is calculated using the formula \(X_L = 2\pi f L\), where \(f\) is the frequency in Hz and \(L\) is the inductance in Henrys. Here, \(f = 60\, \mathrm{Hz}\) and \(L = 35\, \mathrm{mH} = 35 \times 10^{-3}\,\mathrm{H}\).\[X_L = 2\pi (60)(35 \times 10^{-3}) = 13.2\, \Omega\]
02
Calculate Capacitive Reactance
The capacitive reactance \(X_C\) is calculated using \(X_C = \frac{1}{2\pi f C}\), where \(C\) is capacitance in Farads. Given \(C = 26\, \mu\mathrm{F} = 26 \times 10^{-6}\,\mathrm{F}\), the capacitive reactance is calculated as follows: \[X_C = \frac{1}{2\pi (60)(26 \times 10^{-6})} \approx 102.1\, \Omega\]
03
Calculate Total Impedance
The total impedance \(Z\) in an RLC circuit is calculated using \(Z = \sqrt{R^2 + (X_L - X_C)^2}\), where \(R\) is the resistance. Here, \(R = 2.0\, \Omega\). Substitute the values: \[Z = \sqrt{2.0^2 + (13.2 - 102.1)^2} = \sqrt{4 + (-88.9)^2} \approx 89\, \Omega\]
04
Calculate RMS Current
The rms current \(I_{rms}\) is given by \(I_{rms} = \frac{V_{rms}}{Z}\), where \(V_{rms} = 45\, \mathrm{V}\). Therefore: \[I_{rms} = \frac{45}{89} \approx 0.506\, \mathrm{A}\]
05
Calculate Phase Angle
The phase angle \(\phi\) between the current and voltage in a series RLC circuit is calculated by \(\phi = \tan^{-1}\left(\frac{X_L - X_C}{R}\right)\). So, \[\phi = \tan^{-1}\left(\frac{13.2 - 102.1}{2.0}\right) = \tan^{-1}\left(-44.45\right)\approx -88.7^\circ\]
06
Calculate Power Dissipated
The power dissipated in the circuit \(P\) is given by \(P = I_{rms}^2 R\). Substitute the known values: \[P = (0.506)^2 \times 2.0 \approx 0.513\, \mathrm{W}\]
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Inductive Reactance
Inductive reactance is a property of AC circuits that describes how an inductor resists changes in current. It's like a speed bump for alternating current, slowing it down in a way. The formula to determine inductive reactance is given by:\[X_L = 2\pi f L\]where:
- \(X_L\) is the inductive reactance in Ohms (\(\Omega\)).
- \(f\) is the frequency of the AC source.
- \(L\) is the inductance in Henrys.
Capacitive Reactance
Capacitive reactance is somewhat opposite to inductive reactance. It describes how a capacitor resists changes in voltage in an AC circuit. Capacitors store energy in the form of an electric field, and their reactance is calculated using:\[X_C = \frac{1}{2\pi f C}\]where:
- \(X_C\) is the capacitive reactance in Ohms (\(\Omega\)).
- \(C\) is the capacitance in Farads.
Impedance in RLC Circuits
Impedance is a comprehensive measure of the opposition that a circuit presents to the flow of alternating current. In an RLC (resistor-inductor-capacitor) circuit, impedance combines resistance and reactance (both inductive and capacitive) into a single quantity, greatly affecting how an AC circuit behaves.\[Z = \sqrt{R^2 + (X_L - X_C)^2}\]where:
- \(Z\) is the impedance.
- \(R\) is the resistance in Ohms.
- \(X_L\) is the inductive reactance.
- \(X_C\) is the capacitive reactance.