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Find the rms voltage across each element in an \(R L C\) circuit with \(R=9.9 \mathrm{k} \Omega, C=0.15 \mu \mathrm{F},\) and \(L=25 \mathrm{mH}\). The generator supplies an rms voltage of \(115 \mathrm{V}\) at a frequency of \(60.0 \mathrm{Hz}\).

Short Answer

Expert verified
The rms voltages across R, L, and C are approximately 95.46 V, 90.76 V, and 170.47 V, respectively.

Step by step solution

01

Calculate the capacitive reactance (Xc)

The capacitive reactance \( Xc \) can be given by the formula \( Xc = \frac{1}{2 \pi f C} \), where \( f \) is the frequency and \( C \) is the capacitance. Substitute \( f = 60 \text{ Hz} \) and \( C = 0.15 \times 10^{-6} \text{ F} \): \[ Xc = \frac{1}{2 \pi \times 60 \times 0.15 \times 10^{-6}} \approx 17691 \Omega \].
02

Calculate the inductive reactance (Xl)

The inductive reactance \( Xl \) is given by \( Xl = 2 \pi f L \), where \( L \) is the inductance. Substitute \( f = 60 \text{ Hz} \) and \( L = 25 \times 10^{-3} \text{ H} \): \[ Xl = 2 \pi \times 60 \times 25 \times 10^{-3} \approx 9.42 \times 10^{3} \Omega \].
03

Calculate the total impedance (Z)

The total impedance \( Z \) in an RLC circuit is calculated using the formula: \[ Z = \sqrt{R^2 + (Xl - Xc)^2} \]. Substitute the values: \[ Z = \sqrt{(9.9 \times 10^{3})^2 + (9.42 \times 10^{3} - 17.691 \times 10^{3})^2} \approx 11.93 \times 10^{3} \Omega \].
04

Find current from rms voltage

The current \( I \) is found using Ohm's Law: \( I = \frac{V_{rms}}{Z} \), where \( V_{rms} = 115 \text{ V} \). Substitute \( Z = 11.93 \times 10^{3} \Omega \): \[ I = \frac{115}{11.93 \times 10^{3}} \approx 9.64 \times 10^{-3} \text{ A} \].
05

Calculate rms voltage across R

The rms voltage across the resistor \( V_R \) is given by \( V_R = I \times R \). Substitute \( R = 9.9 \times 10^3 \Omega \): \[ V_R = 9.64 \times 10^{-3} \times 9.9 \times 10^{3} \approx 95.46 \text{ V} \].
06

Calculate rms voltage across L

The rms voltage across the inductor \( V_L \) is \( V_L = I \times Xl \). Substitute \( Xl = 9.42 \times 10^{3} \Omega \): \[ V_L = 9.64 \times 10^{-3} \times 9.42 \times 10^{3} \approx 90.76 \text{ V} \].
07

Calculate rms voltage across C

The rms voltage across the capacitor \( V_C \) is \( V_C = I \times Xc \). Substitute \( Xc \approx 17.691 \times 10^{3} \Omega \): \[ V_C = 9.64 \times 10^{-3} \times 17.691 \times 10^{3} \approx 170.47 \text{ V} \].

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Capacitive Reactance
Understanding capacitive reactance is crucial when analyzing RLC circuits. Capacitive reactance, denoted as \( X_c \), represents the opposition to the flow of alternating current (AC) due to the presence of a capacitor. It is calculated using the formula \( X_c = \frac{1}{2 \pi f C} \), where \( f \) is the frequency of the AC source, and \( C \) is the capacitance. Essentially, as frequency or capacitance increases, the capacitive reactance decreases.

In our exercise, using a frequency of 60 Hz and a capacitance of 0.15 \( \mu \text{F} \), the capacitive reactance is approximately 17691 \( \Omega \). This high value indicates a strong opposition to the current, meaning that capacitors are less effective at conducting current at lower frequencies.
Inductive Reactance
Inductive reactance measures how much the inductor resists the change of current in an AC circuit. It is denoted as \( X_l \) and can be calculated using the formula \( X_l = 2 \pi f L \), where \( L \) represents inductance. As the frequency or inductance increases, so does the inductive reactance.

In the example provided, with 60 Hz as the frequency and an inductance of 25 mH, the inductive reactance is roughly \( 9.42 \times 10^{3} \Omega \). This value tells us how much the inductor opposes the current flow. Unlike capacitors, inductors are more resistive at higher frequencies, where they significantly impedes current flow.
Ohm's Law
Ohm's Law forms the backbone of electrical circuit analysis, particularly in RLC circuits. This law states that the current through a conductor between two points is directly proportional to the voltage across the two points. It is summed up by the equation \( I = \frac{V}{Z} \), where \( I \) is the current, \( V \) is the voltage, and \( Z \) is the impedance.
  • Ohm's Law helps us determine the current flowing through the circuit that is subject to a total impedance.
  • We can also use it in a rearranged form to solve for voltage or impedance when the other variables are known.
In the context of our exercise, using a supplied rms voltage of 115 V and a calculated total impedance \( Z \) around 11.93 k\( \Omega \), the current in the circuit is approximately \( 9.64 \times 10^{-3} \) A.
Total Impedance
The total impedance \( Z \) in an RLC circuit combines resistance, capacitive reactance, and inductive reactance. Impedance is the effective resistance in AC circuits, and it is a vector sum calculated using the formula \( Z = \sqrt{R^2 + (X_l - X_c)^2} \).

This shows how resistance \( R \), and the difference between inductive \( X_l \) and capacitive \( X_c \) reactance, affect the overall opposition to the current. In our scenario, with resistance 9.9 k\( \Omega \), inductive reactance 9.42 k\( \Omega \), and capacitive reactance approximately 17.691 k\( \Omega \), the total impedance is found to be about 11.93 k\( \Omega \).
  • This impedance affects the current that can flow through the circuit under a given voltage.
  • Understanding total impedance is vital for analyzing power consumption and signal behavior in AC circuits.
RMS Voltage
Root Mean Square (RMS) voltage is a critical concept in AC circuits. It refers to the effective value of varying voltage and is comparable to a constant DC voltage when it comes to power delivery.

RMS voltage is essential for calculating current and power values in AC circuits, using the root mean square form: \( V_{rms} = \frac{V_{peak}}{\sqrt{2}} \).
  • For our circuit, the RMS voltage across the generator is 115 V, used to calculate currents and voltages across different components in the circuit.
  • RMS values give us a straightforward understanding of how much true voltage or current is present effectively, for both resistive and reactive components.
The voltage across individual components can be found by multiplying RMS current with their respective impedance, making it very relevant when performing complex RLC circuit analysis.

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Most popular questions from this chapter

\- An rms voltage of \(120 \mathrm{V}\) produces a maximum current of \(2.1 \mathrm{A}\) in a certain resistor. Find the resistance of this resistor.

European Electricity In many European homes the rms voltage available from a wall socket is 240 V . What is the maximum voltage in this case?

Manufacturing Plant Power A manufacturing plant uses \(2.22 \mathrm{kW}\) of electric power provided by a \(60.0-\mathrm{Hz}\) ac generator with an rms voltage of 485 V. The plant uses this power to run a number of high-inductance electric motors. The plant's total resistance is \(R=25.0 \Omega\) and its inductive reactance is \(X_{L}=45.0 \Omega .\) (a) What is the total impedance of the plant? (b) What is the plant's power factor? (c) What is the rms current used by the plant? (d) What capacitance, connected in series with the power line, will increase the plant's power factor to unity? (e) If the power factor is unity, how much current is needed to provide the \(2.22 \mathrm{kW}\) of power needed by the plant? Compare your answer with the current found in part (c). (Because power- line losses are proportional to the square of the current, a utility company will charge an industrial user with a low power factor a higher rate per \(\mathrm{kWh}\) than a company with a power factor close to unity.)

The rms current in an \(R L\) circuit is \(0.26 \mathrm{A}\) when it is connected to an ac generator with a frequency of \(60.0 \mathrm{Hz}\) and an (a) Given that the inductor has an inducrms voltage of 25 V. tance of \(145 \mathrm{mH},\) what is the resistance of the resistor? (b) Find the rms voltage across the resistor. (c) Find the rms voltage across the inductor. (d) Use your results from parts (b) and (c) to show that \(\sqrt{V_{\mathrm{rms}, R}^{2}+V_{\mathrm{rms}, l}^{2}}\) is equal to 25 V.

\(\mathrm{CE}\) An inductor in an \(L C\) circuit has a maximum current of \(2.4 \mathrm{A}\) and a maximum energy of \(36 \mathrm{mJ}\). When the current in the inductor is \(1.2 \mathrm{A},\) what is the energy stored in the capacitor?

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