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IP An rms voltage of \(22.2 \mathrm{V}\) with a frequency of \(1.00 \mathrm{kHz}\) is applied to a \(0.290-\mathrm{mH}\) inductor. (a) What is the rms current in this circuit? (b) By what factor does the current change if the frequency of the voltage is doubled? (c) Calculate the current for a frequency of \(2.00 \mathrm{kHz}\)

Short Answer

Expert verified
(a) 12.18 A; (b) Current halves; (c) 6.09 A at 2.00 kHz.

Step by step solution

01

Calculate the inductive reactance at 1.00 kHz

The inductive reactance (\(X_L\)) is calculated using the formula \(X_L = 2 \pi f L\). Substituting the given values, \(f = 1.00 \text{kHz} = 1000 \text{Hz}\) and \(L = 0.290 \text{ mH} = 0.290 \times 10^{-3} \text{ H}\), we get: \[ X_L = 2 \pi \times 1000 \times 0.290 \times 10^{-3} = 1.823 \text{ ohms}\]
02

Calculate the rms current at 1.00 kHz

Use Ohm's law for AC circuits, \(I_{rms} = \frac{V_{rms}}{X_L}\). Given \(V_{rms} = 22.2 \text{ V}\) and \(X_L = 1.823 \text{ ohms}\), calculate the current:\[ I_{rms} = \frac{22.2}{1.823} = 12.18 \text{ A} \]
03

Determine the factor change in current when frequency is doubled

Doubling the frequency alters the inductive reactance: \(X_L' = 2 \pi (2f) L = 2 \times X_L = 2 \times 1.823 \text{ ohms} = 3.646 \text{ ohms}\). Using the relation \(I_{rms}' = \frac{V_{rms}}{X_L'}\), we see that the new current is: \[ I_{rms}' = \frac{22.2}{3.646} = 6.09 \text{ A} \]The factor by which the current changes is \( \frac{I_{rms}'}{I_{rms}} = \frac{6.09}{12.18} \approx 0.5\). Thus, the current halves.
04

Calculate the rms current at 2.00 kHz

Using the updated reactance from Step 3, \(X_L' = 3.646 \text{ ohms}\), the current at the new frequency can be calculated with: \[ I_{rms} = \frac{22.2}{3.646} \approx 6.09 \text{ A} \]

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Key Concepts

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

Understanding RMS Current Calculation
RMS, or root mean square, is a statistical measure used in various fields to represent the magnitude of a varying quantity. In electrical circuits, especially AC (Alternating Current) circuits, RMS is crucial in determining the effective value of an alternating voltage or current.
For calculating the RMS current in an AC circuit involving an inductor, you need to use Ohm's law for AC, which states that:
  • Voltage across an inductor: \( V_{rms} \)
  • Inductive reactance: \( X_L = 2\pi f L \)
  • Current: \( I_{rms} = \frac{V_{rms}}{X_L} \)
In the given exercise, the inductive reactance at a specified frequency and inductance is computed, allowing for the determination of the current. Applying the formula at 1 kHz and using the known \( V_{rms} \) value, the current is calculated to be approximately 12.18 A.
Ohm's Law for AC Circuits Explained
Ohm's law is a fundamental principle often used to describe the relationship between voltage, current, and impedance in electrical circuits. For AC circuits, the law adapts to account for the phase difference between voltage and current due to reactance. Instead of resistance, we use impedance, which, in the case of an inductor, manifests as inductive reactance \( X_L \).
The formula used is slightly altered to \( I_{rms} = \frac{V_{rms}}{X_L} \), where \( V_{rms} \) is the RMS voltage across the component, and \( X_L \) represents inductive reactance.
Ohm's law for AC circuits helps us effortlessly calculate either the voltage, current, or reactance, provided we know the other two quantities, demonstrating its pivotal role.
Applying this concept to the exercise, knowing the inductive reactance and \( V_{rms} \), helps find the RMS current in both scenarios of different frequencies.
Exploring Frequency and Current Relationship
In AC circuits involving inductors, the frequency of the applied voltage plays a key role in determining the inductive reactance.The inductive reactance is directly proportional to the frequency, calculated as \( X_L = 2 \pi f L \). Thus, if the frequency increases, the inductive reactance also rises, impacting the current flow.
Increasing frequency results in higher reactance, which reduces the current flow through the inductor. This is why, in our exercise, when the frequency doubles, the reactance doubles, causing the current to half.
Understanding the relationship between frequency and current in AC circuits allows better design and analysis, ensuring components operate within their desired specifications.
If you know the frequency is doubled, for example, you are prepared to adjust your system or expect a change in behavior as you saw in the calculation where the current was reduced to approximately 6.09 A.

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Most popular questions from this chapter

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.

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