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In an oscillating \(L C\) circuit with \(L=50 \mathrm{mH}\) and \(C=4.0 \mu \mathrm{F},\) the current is initially a maximum. How long will it take before the capacitor is fully charged for the first time?

Short Answer

Expert verified
The capacitor will be fully charged for the first time in approximately 222 microseconds.

Step by step solution

01

Formula for the Resonant Frequency

The resonant angular frequency \( \omega \) of an LC circuit is given by the formula: \[ \omega = \frac{1}{\sqrt{LC}} \] This formula allows us to determine how quickly the circuit oscillates.
02

Substitute the Given Values

We have \( L = 50 \text{ mH} = 50 \times 10^{-3} \text{ H}\) and \( C = 4.0 \mu\text{F} = 4.0 \times 10^{-6} \text{ F} \). Substitute these values into the formula:\[ \omega = \frac{1}{\sqrt{(50 \times 10^{-3})(4.0 \times 10^{-6})}} \]
03

Calculate the Resonant Angular Frequency

Perform the calculation to find \( \omega \):\[ \omega = \frac{1}{\sqrt{(50 \times 10^{-3})(4.0 \times 10^{-6})}} = \frac{1}{\sqrt{200 \times 10^{-9}}} = \frac{1}{\sqrt{2 \times 10^{-7}}} \approx 7071 \text{ rad/s} \]
04

Determine the Time for Maximum Charge

The charge in the LC circuit will be maximum at a quarter of the oscillation period, \( T \). The period \( T \) is calculated using:\[ T = \frac{2\pi}{\omega} \]Thus, the time for the capacitor to be fully charged for the first time \( t = \frac{T}{4} \).
05

Calculate the Oscillation Period

Substitute \( \omega \) into the period formula:\[ T = \frac{2\pi}{7071} \approx 0.000888 \text{ s} \]
06

Calculate the Time for First Full Charge

Now divide \( T \) by 4 to find the time for the capacitor to be fully charged:\[ t = \frac{0.000888}{4} \approx 0.000222 \text{ s} = 222 \mu \text{s} \]

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Key Concepts

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

Resonant Frequency
In an LC circuit, the "resonant frequency" is one of the most important characteristics. The resonant frequency determines how fast the circuit can oscillate. It is defined by the formula: \[ \omega = \frac{1}{\sqrt{LC}} \] This formula uses the inductance \( L \) and capacitance \( C \) to set the stage for the circuit's behavior.

When the circuit reaches its resonant frequency, energy moves back and forth between the inductor and the capacitor at its most efficient rate. In our solution, the inductor \( L \) was 50 mH and the capacitor \( C \) was 4.0 μF. By plugging these values into the formula, we calculated the resonant angular frequency \( \omega \) to be approximately 7071 rad/s.

Understanding the resonant frequency helps in anticipating the circuit's dynamic response, especially when it oscillates without any external influence. This concept is fundamental in tuning circuits to desired frequencies and ensuring minimal energy loss during oscillations.
Oscillation Period
An "oscillation period" in an LC circuit is essentially the time it takes for the system to complete one full cycle of charge and discharge. The period \( T \) can be determined using the formula based on the resonant frequency:\[ T = \frac{2\pi}{\omega} \] This gives us a clear idea of how quickly or slowly the current and voltage waveforms repeat themselves in the circuit.

In the given exercise, after determining \( \omega \approx 7071 \text{ rad/s} \), we calculated the oscillation period \( T \) to be approximately 0.000888 seconds. This value informs us that the LC circuit oscillates rapidly, completing almost a full cycle in less than a millisecond.

An understanding of the oscillation period is crucial, especially when designing circuits that must synchronize or work well with other timed processes. It also helps in predicting when certain values, like maximum voltage or current, will occur constantly within each cycle.
Capacitor Charge Time
The "capacitor charge time" is a key concept when analyzing the dynamics of an LC circuit. It refers to the moment when the capacitor reaches its maximum charge, which occurs at specific intervals.

In an LC circuit starting at maximum current, the capacitor becomes fully charged for the first time at one-quarter of the oscillation period \( T \). This is because during the first quarter of the period, the energy stored in the inductor transfers fully to the capacitor until it's maximally charged.

The calculation for the charge time is straightforward:\[ t = \frac{T}{4} \] Using the previously calculated period \( T = 0.000888 \text{ s} \), the time taken for the first maximum charge is about 222 microseconds.

Knowing the time it takes for a capacitor to fully charge is essential, especially in applications where timing and synchronization are crucial. It helps engineers and physicists to design better timing systems and workers in planning effective power distribution within a circuit.

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Most popular questions from this chapter

An alternating source drives a series \(R L C\) circuit with an emf amplitude of \(6.00 \mathrm{~V},\) at a phase angle of \(+30.0^{\circ} .\) When the potential difference across the capacitor reaches its maximum positive value of \(+5.00 \mathrm{~V},\) what is the potential difference across the inductor (sign included)?

A series \(R L C\) circuit is driven by a generator at a frequency of \(2000 \mathrm{~Hz}\) and an emf amplitude of \(170 \mathrm{~V}\). The inductance is \(60.0 \mathrm{mH},\) the capacitance is \(0.400 \mu \mathrm{F},\) and the resistance is \(200 \Omega .\) (a) What is the phase constant in radians? (b) What is the current amplitude?

A variable capacitor with a range from 10 to \(365 \mathrm{pF}\) is used with a coil to form a variable-frequency \(L C\) circuit to tune the input to a radio. (a) What is the ratio of maximum frequency to minimum frequency that can be obtained with such a capacitor? If this circuit is to obtain frequencies from \(0.54 \mathrm{MHz}\) to \(1.60 \mathrm{MHz}\), the ratio computed in (a) is too large. By adding a capacitor in parallel to the variable capacitor, this range can be adjusted. To obtain the desired frequency range, (b) what capacitance should be added and (c) what inductance should the coil have?

What resistance \(R\) should be connected in series with an inductance \(L=220 \mathrm{mH}\) and capacitance \(C=12.0 \mu \mathrm{F}\) for the maximum charge on the capacitor to decay to \(99.0 \%\) of its initial value in 50.0 cycles? (Assume \(\left.\omega^{\prime} \approx \omega .\right)\)

A generator supplies \(100 \mathrm{~V}\) to a transformer's primary coil, which has 50 turns. If the secondary coil has 500 turns, what is the secondary voltage?

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