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\( \quad L C\) oscillators have been used in circuits connected to loudspeakers to create some of the sounds of electronic music. What inductance must be used with a \(3.4 \mu \mathrm{F}\) capacitor to produce a frequency of \(10 \mathrm{kHz}\), which is near the middle of the audible range of frequencies?

Short Answer

Expert verified
The required inductance is approximately 7.0 mH.

Step by step solution

01

Understand the Formula

The frequency of an LC oscillator is given by the formula: \[ f = \frac{1}{2\pi\sqrt{LC}} \]where \(f\) is the frequency, \(L\) is the inductance, and \(C\) is the capacitance.
02

Rearrange the Formula for L

To find the inductance \( L \), rearrange the formula:\[ L = \frac{1}{(2\pi f)^2 C} \]
03

Insert Known Values

Substitute the known values into the formula:- Frequency \(f = 10^4 \text{ Hz}\)- Capacitance \(C = 3.4 \times 10^{-6} \text{ F}\)\[ L = \frac{1}{(2\pi \times 10^4)^2 \times 3.4 \times 10^{-6}} \]
04

Calculate the Inductance

Calculate the numerical value of \(L\): \[ L = \frac{1}{(2 \times 3.1416 \times 10^4)^2 \times 3.4 \times 10^{-6}} \] \[ L \approx 7.0 \times 10^{-3} \text{ H} \] Convert to millihenries: \[ L \approx 7.0 \text{ mH} \]

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Key Concepts

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

Inductance Calculation
Inductance, denoted by \( L \), is a fundamental property of an LC oscillator circuit, determining how much an inductor resists changes in current. Calculating the inductance required to achieve a desired frequency involves rearranging the oscillator frequency formula \( f = \frac{1}{2\pi\sqrt{LC}} \). This formula shows how the frequency \( f \), capacitance \( C \), and inductance \( L \) are related.

To find \( L \), we rearrange the formula to solve for inductance:
  • First, square both sides: \( f^2 = \frac{1}{(2\pi)^2 LC} \)
  • Next, isolate \( L \): \( L = \frac{1}{(2\pi f)^2 C} \)
This equation shows that when you know the frequency of the circuit and the capacitance, you can calculate the necessary inductance by plugging the values into this formula. In the example, using a frequency of \( 10 \text{ kHz} \) and a capacitance of \( 3.4 \mu \text{F} \) results in an inductance \( L \) of approximately \( 7.0 \text{ mH} \). This calculation is essential in the design and tuning of oscillators where specific frequencies are needed.
Frequency of LC Circuit
The frequency of an LC circuit, formed by inductors and capacitors, is important in various electronic applications, including those in audio and radio frequency domains. The frequency at which an LC circuit oscillates is primarily determined by its inductance and capacitance.

The basic formula for determining this frequency is:
  • \( f = \frac{1}{2\pi\sqrt{LC}} \)
Here, \( f \) represents the frequency in Hertz (Hz), \( L \) is the inductance in Henrys (H), and \( C \) is the capacitance in Farads (F). This relationship shows that frequency is inversely proportional to the square root of the product of \( L \) and \( C \).

Adjusting either the inductance or capacitance in the circuit directly changes the oscillation frequency. This is why inductors and capacitors are often used together to create tuning circuits, allowing precise control over the frequency of oscillation.
Capacitance
Capacitance is a measure of a capacitor's ability to store charge and is a key component in an LC circuit, influencing the frequency of oscillation. Represented by \( C \) and measured in Farads (F), capacitance interacts with inductance to determine the behavior of an LC oscillator.

In the context of LC circuits:
  • Capacitors store electrical energy as an electric field, which contributes to the total energy stored in the circuit.
  • The energy alternates back and forth between electric and magnetic fields, creating characteristic oscillations at the resonant frequency \( f \) given by \( \frac{1}{2\pi\sqrt{LC}} \).
The precise value of capacitance in a circuit helps set its oscillation frequency. For example, in the problem statement, a capacitance of \( 3.4 \mu \text{F} \) is used. When paired with an appropriate inductor, it ensures that the circuit oscillates at the desired \( 10 \text{ kHz} \) frequency. Understanding and choosing the correct capacitance is vital for achieving the desired frequency response in an LC oscillator.

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Most popular questions from this chapter

In an oscillating \(L C\) circuit, \(L=3.00 \mathrm{mH}\) and \(C=3.90 \mu \mathrm{F}\). At \(t=0\) the charge on the capacitor is zero and the current is \(1.75 \mathrm{~A}\). (a) What is the maximum charge that will appear on the capacitor? (b) At what earliest time \(t>0\) is the rate at which energy is stored in the capacitor greatest, and (c) what is that greatest rate?

A generator supplies \(100 \mathrm{~V}\) to a transformer's primary coil, which has 100 turns. If the secondary coil has 500 turns, what is the secondary voltage?

In an oscillating \(L C\) circuit in which \(C=6.00 \mu \mathrm{F}\), the maximum potential difference across the capacitor during the oscillations is \(1.50 \mathrm{~V}\) and the maximum current through the inductor is \(50.0 \mathrm{~mA}\). What are (a) the inductance \(L\) and (b) the frequency of the oscillations? (c) How much time is required for the charge on the capacitor to rise from zero to its maximum value?

(a) At what frequency would a \(12 \mathrm{mH}\) inductor and a \(10 \mu \mathrm{F}\) capacitor have the same reactance? (b) What would the reactance be? (c) Show that this frequency would be the natural frequency of an oscillating circuit with the same \(L\) and \(C\).

An alternating emf source with a variable frequency \(f_{d}\) is connected in series with a \(50.0 \Omega\) resistor and a \(28.0 \mu \mathrm{F}\) capacitor. The emf amplitude is \(12.0 \mathrm{~V}_{-}\)(a) Draw a phasor diagram for phasor \(V_{R}\) (the potential across the resistor) and phaser \(V_{C}\) (the potential across the capacitor). (b) At what driving frequency \(f_{d}\) do the two phasors have the same length? At that driving frequency, what are (c) the phase angle in degrees, (d) the angular speed at which the phasors rotate, and (e) the current amplitude?

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