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In a certain \(L R C\) series circuit, when the ac voltage source has a particular frequency \(f,\) the peak voltage across the inductor is 6.0 times greater than the peak voltage across the capacitor. Determine \(f\) in terms of the resonant frequency \(f_{0}\) of this circuit.

Short Answer

Expert verified
The frequency \( f \) is \( \sqrt{6} \cdot f_0 \).

Step by step solution

01

Understand the Given Information

In a series LRC circuit, it's given that the peak voltage across the inductor is 6.0 times the peak voltage across the capacitor at a certain frequency \( f \). We need to find \( f \) in terms of the resonant frequency \( f_0 \).
02

Recall the Relationship Between Inductor and Capacitor Voltages

In a resonant LRC circuit, the impedance of the inductor \( Z_L = j\omega L \) and the capacitor \( Z_C = \frac{-j}{\omega C} \), where \( \omega = 2\pi f \) is the angular frequency. At resonance, \( \omega = \omega_0 \) and \( \omega_0 = \frac{1}{\sqrt{LC}} \).
03

Use the Voltage Ratio Condition

Given \( V_L = 6V_C \), where \( V_L = I \cdot Z_L \) and \( V_C = I \cdot Z_C \). Thus, \( \omega L = 6 \cdot \frac{1}{\omega C} \). Solve this equation: \( \omega^2 = \frac{6}{LC} \).
04

Relate Omega and Frequency

The resonant frequency \( \omega_0 \) is given by \( \omega_0 = \frac{1}{\sqrt{LC}} \). Therefore, \( \omega^2 = 6 \cdot \omega_0^2 \). By taking the square root on both sides, \( \omega = \sqrt{6} \cdot \omega_0 \).
05

Convert to Frequency

Since \( \omega = 2\pi f \), we have \( 2\pi f = \sqrt{6} \cdot 2\pi f_0 \). Thus, \( f = \sqrt{6} \cdot f_0 \).
06

Statement of the Result

The frequency \( f \) in terms of the resonant frequency \( f_0 \) is \( f = \sqrt{6} \cdot f_0 \).

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Key Concepts

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

Resonant Frequency
The concept of resonant frequency is crucial in understanding LRC circuits. It refers to the particular frequency at which the impedances of the inductor and capacitor, which have opposite reactive behaviors, cancel each other out. This cancellation leads to a circuit that is purely resistive, with zero reactive impedance, making the current and voltage in phase.

In mathematical terms, the resonant frequency \( f_0 \) is determined by the formula:\[\omega_0 = \frac{1}{\sqrt{LC}}\]where \( \omega_0 = 2\pi f_0 \), \( L \) is the inductance, and \( C \) is the capacitance. The resonant frequency depends solely on these two factors, indicating the ideal frequency for energy transfer in an LRC circuit.

At this frequency, the power factor hits its peak, and the circuit has minimum impedance. This is immensely useful in applications like tuning radios to the desired frequency or designing filters and oscillators, as it optimizes the circuit's performance.
Inductance and Capacitance Relationship
In an LRC circuit, inductance \( L \) and capacitance \( C \) are key elements that determine the overall behavior of the circuit. Inductors and capacitors store energy, with inductors storing it in a magnetic field and capacitors in an electric field. Their relationship is fundamental to deriving the resonant frequency and understanding the dynamic behavior of the circuit.

**Key Points:**
  • The impedance of an inductor \( Z_L = j \omega L \) is directly proportional to frequency (\( \omega \)).
  • The impedance of a capacitor \( Z_C = \frac{-j}{\omega C} \) is inversely proportional to frequency.
When analyzing the condition \( V_L = 6V_C \) in the exercise, we equate current expressions to find:\[\omega L = 6 \times \left(\frac{1}{\omega C}\right)\]Solving this gives \( \omega^2 = \frac{6}{LC} \), illustrating how these two components interact in driving circuit behavior under certain conditions.
Angular Frequency
Angular frequency \( \omega \) represents how often an object rotates through a complete cycle. It is directly related to the frequency of the oscillations in the circuit, and in LRC circuits, it ties the resonant frequency with the normal operating frequency. This is because \( \omega = 2\pi f \), where \( f \) is the frequency in hertz (Hz), representing cycles per second.

In the context of the given problem, we explore how angular frequency defines the voltage relationship between components at a specified condition. We use the voltage ratio expression to derive:\[\omega^2 = 6 \times \omega_0^2\]Taking the square root, we find that \( \omega = \sqrt{6} \times \omega_0 \), showing that the angular frequency at which the condition \( V_L = 6V_C \) holds, is directly connected through a factor of \( \sqrt{6} \) to the resonant frequency.

This concept is crucial as it helps determine how a circuit behaves at different frequencies, allowing for strategic adjustments in real-world applications.

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Most popular questions from this chapter

Calculate the reactance of, and rms current in, a \(36.0-\mathrm{mH}\) radio coil connected to a \(250-\mathrm{V}(\mathrm{rms}) 33.3-\mathrm{kHz}\) ac line. Ignore resistance.

(II) ( \(a\) ) Determine a formula for the average power \(\bar{P}\) dissipated in an \(L R C\) circuit in terms of \(L, R, C, \omega,\) and \(V_{0}\) (b) At what frequency is the power a maximum? (c) Find an approximate formula for the width of the resonance peak in average power, \(\Delta \omega\), which is the difference in the two (angular) frequencies where \(\bar{P}\) has half its maximum value. Assume a sharp peak.

An \(L R\) circuit can be used as a "phase shifter." Assume that an "input" source voltage \(V=V_{0} \sin (2 \pi f t+\phi)\) is connected across a series combination of an inductor \(L=55 \mathrm{mH}\) and resistor \(R .\) The "output" of this circuit is taken across the resistor. If \(V_{0}=24 \mathrm{~V}\) and \(f=175 \mathrm{~Hz}\) determine the value of \(R\) so that the output voltage \(V_{R}\) lags the input voltage \(V\) by \(25^{\circ} .\) Compare (as a ratio) the peak output voltage with \(V_{0}\).

A \(10.0-\mathrm{k} \Omega\) resistor is in series with a \(26.0-\mathrm{mH}\) inductor and an ac source. Calculate the impedance of the circuit if the source frequency is (a) \(55.0 \mathrm{~Hz}\); (b) \(55,000 \mathrm{~Hz}\).

(II) Capacitors made from piezoelectric materials are commonly used as sound transducers ("speakers"). They often require a large operating voltage. One method for providing the required voltage is to include the speaker as part of an \(L R C\) circuit as shown in Fig. \(29 ,\) where the speaker is modeled electrically as the capacitance \(C = 1.0 \mathrm { nF } .\) Take \(R = 35 \Omega\) and \(L = 55 \mathrm { mH } .\) (a) What is the resonant frequency \(f _ { 0 }\) for this circuit? (b) If the voltage source has peak amplitude \(V _ { 0 } = 2.0 \mathrm { V }\) at frequency \(f = f _ { 0 } ,\) find the peak voltage \(V _ { c 0 }\) across the speaker (i.e., the capacitor \(C\) ). (c) Determine the ratio \(V _ { C 0 } / V _ { 0 . }\)

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