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\(\bullet \mathrm{A} 4.40-\mu \mathrm{F}\) and an \(8.80-\mu \mathrm{F}\) capacitor are connected in series to a \(60.0-\mathrm{Hz}\) generator operating with an \(\mathrm{rms}\) voltage of \(115 \mathrm{V} .\) What is the rms current supplied by the generator?

Short Answer

Expert verified
The rms current supplied by the generator is approximately 0.127 A.

Step by step solution

01

Understand the Series Connection

When capacitors are connected in series, the equivalent capacitance \( C_{eq} \) can be found using the formula: \( \frac{1}{C_{eq}} = \frac{1}{C_1} + \frac{1}{C_2} \), where \( C_1 = 4.40 \, \mu F \) and \( C_2 = 8.80 \, \mu F \).
02

Calculate Equivalent Capacitance

Substitute the values into the capacitance formula: \( \frac{1}{C_{eq}} = \frac{1}{4.40} + \frac{1}{8.80} \). Calculate each term: \( \frac{1}{4.40} = 0.227 \) \((\mu F)^{-1}\) and \( \frac{1}{8.80} = 0.114 \) \((\mu F)^{-1}\). Summing these gives \( \frac{1}{C_{eq}} = 0.341 \). The equivalent capacitance \( C_{eq} \) is then \( \frac{1}{0.341} \approx 2.93 \, \mu F \).
03

Convert Capacitance to Farads

Convert \( C_{eq} \) to farads for calculations: \( 2.93 \, \mu F = 2.93 \times 10^{-6} \, F \).
04

Determine Capacitive Reactance

The capacitive reactance \( X_c \) is given by \( X_c = \frac{1}{2\pi f C_{eq}} \) where \( f = 60.0 \, Hz \) and \( C_{eq} = 2.93 \times 10^{-6} \, F \). Substituting the values, \( X_c = \frac{1}{2\pi \times 60.0 \times 2.93 \times 10^{-6}} \).
05

Calculate Capacitive Reactance

Calculate the capacitive reactance: \( X_c = \frac{1}{1.106 \times 2.93 \times 10^{-6}} \approx 905 \) ohms.
06

Use Ohm's Law for AC Circuits

In AC circuits, the rms current \( I_{rms} \) equals \( \frac{V_{rms}}{X_c} \), where \( V_{rms} = 115 \, V \) and \( X_c = 905 \, \Omega \). Substituting these values gives: \( I_{rms} = \frac{115}{905} \approx 0.127 \, A \).
07

State the Solution

The rms current supplied by the generator is approximately \( 0.127 \, A \).

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Key Concepts

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

Equivalent Capacitance
When dealing with capacitors in series, it's critical to understand how equivalent capacitance is calculated. Unlike resistors where you simply add up their values for a series connection, capacitors in series behave a bit differently. The formula used for finding the equivalent capacitance \( C_{eq} \) is \( \frac{1}{C_{eq}} = \frac{1}{C_1} + \frac{1}{C_2} + \ldots + \frac{1}{C_n} \). Here, \( C_1 \) and \( C_2 \) are the capacitance values of the capacitors in series.

For our specific problem, we have a \( 4.40-\mu F \) and an \( 8.80-\mu F \) capacitor. Substituting these into the formula gives \( \frac{1}{C_{eq}} = 0.227 + 0.114 = 0.341 \). Thus, \( C_{eq} = \frac{1}{0.341} \approx 2.93 \, \mu F \).

It's essential to convert microfarads to farads since farad is the standard unit of capacitance used in calculations. This means \( 2.93 \, \mu F = 2.93 \times 10^{-6} \, F \). Understanding this process is fundamental to accurately dealing with capacitors in series in any electrical circuit.
Capacitive Reactance
Capacitive reactance plays a crucial role in AC circuits, especially when it comes to determining how much a capacitor opposes the current flow. It is denoted by \( X_c \) and can be computed using the formula \( X_c = \frac{1}{2\pi f C} \), where \( f \) is the frequency and \( C \) is the capacitance.

In our example, with a frequency \( f = 60.0 \, Hz \) and an equivalent capacitance \( C = 2.93 \times 10^{-6} \, F \), the capacitive reactance is calculated as \( X_c = \frac{1}{2 \pi \times 60.0 \times 2.93 \times 10^{-6}} \).

After going through the calculations, we find \( X_c \approx 905 \, \Omega \). This value tells us how much the capacitors are impeding the current flow in the circuit. A higher capacitive reactance means a greater opposition to current flow, which is vital information when analyzing AC circuits.
RMS Current
Root Mean Square (RMS) current is a key factor in AC circuits, especially when we want to find how much current flows through the circuit for real-world AC applications. RMS values provide a meaningful representation of alternating current levels. In this context, the RMS current \( I_{rms} \) can be computed using Ohm’s Law for AC circuits.

The formula is \( I_{rms} = \frac{V_{rms}}{X_c} \), where \( V_{rms} \) is the root mean square voltage and \( X_c \) is the capacitive reactance. Given \( V_{rms} = 115 \, V \) and \( X_c = 905 \, \Omega \), the calculation is \( I_{rms} = \frac{115}{905} \approx 0.127 \, A \).

This value represents how much alternating current (AC) is effectively flowing through the circuit. Understanding RMS current is crucial for grasping the behavior of AC circuits and ensuring their efficient operation.

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Most popular questions from this chapter

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.)

A 9.5-Hz generator is connected to a capacitor. If the current in the generator has its maximum value at \(t=0,\) what is the earliest possible time that the voltage across the capacitor is a maximum?

An inductor has a reactance of \(56.5 \Omega\) at \(75.0 \mathrm{Hz}\). What is its reactance at \(60.0 \mathrm{Hz}\) ?

\(\cdot\) An \(R L C\) circuit has a capacitance of \(0.29 \mu F\), (a) What inductance will produce a resonance frequency of \(95 \mathrm{MHz} ?\) (b) It is desired that the impedance at resonance be one-fifth the impedance at \(11 \mathrm{kHz}\). What value of \(R\) should be used to obtain this result?

IP A circuit is constructed by connecting a \(1.00-\mathrm{k} \Omega\) resistor, a \(252-\mu \mathrm{F}\) capacitor, and a \(515-\mathrm{mH}\) inductor in series. (a) What is the highest frequency at which the impedance of this circuit is equal to \(2.00 \mathrm{k} \Omega ?\) (b) To reduce the impedance of this circuit, should the frequency be increased or decreased from its value in part (a)? Explain.

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