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Question

An alternating voltage has the equation V(t) = 200 sin 377t V. What is the value of r.m.s. voltage and frequency?

The correct answer is
\(\frac{200}{\sqrt{2}}\) V, 60 Hz

Alternating Voltage Equation Analysis

The given equation for the alternating voltage is V(t) = 200 sin 377t V.

This equation is in the standard form of an alternating voltage:

\[ V(t) = V_0 \sin(\omega t) \]

Where:

  • \(V_0\) is the peak voltage or maximum voltage.
  • \(\omega\) is the angular frequency in radians per second.
  • t is the time in seconds.

Identifying Peak Voltage and Angular Frequency

Comparing the given equation V(t) = 200 sin 377t V with the standard form \(V(t) = V_0 \sin(\omega t)\), we can identify the values:

  • Peak voltage, \(V_0 = 200\) V
  • Angular frequency, \(\omega = 377\) rad/s

Calculating RMS Voltage

The root mean square (r.m.s.) voltage for a sinusoidal alternating voltage is related to the peak voltage by the formula:

\[ V_{rms} = \frac{V_0}{\sqrt{2}} \]

Substitute the peak voltage \(V_0 = 200\) V into the formula:

\[ V_{rms} = \frac{200}{\sqrt{2}} \text{ V} \]

Calculating Frequency

The angular frequency (\(\omega\)) is related to the frequency (f) in Hertz (Hz) by the formula:

\[ \omega = 2\pi f \]

We have \(\omega = 377\) rad/s. We can rearrange the formula to solve for the frequency f:

\[ f = \frac{\omega}{2\pi} \]

Substitute the value of \(\omega\):

\[ f = \frac{377}{2\pi} \text{ Hz} \]

To find the numerical value, we can approximate \(2\pi \approx 2 \times 3.14159 = 6.28318\).

\[ f \approx \frac{377}{6.28318} \approx 59.99 \text{ Hz} \]

This value is very close to 60 Hz. In electrical engineering contexts, 377 rad/s is commonly used as an approximation for \(120\pi\) rad/s, which corresponds exactly to 60 Hz (\(120\pi \approx 376.99\)).

Therefore, the frequency is 60 Hz.

Summary of Results

Based on the calculations:

  • R.M.S. voltage = \(\frac{200}{\sqrt{2}}\) V
  • Frequency = 60 Hz

These values correspond to one of the given options.

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Important Questions from RMS Value of Time Varying Waveforms

  1. RMS value is defined based on which of the following?

  2. Which of the following methods used for average value determination is convenient for non-sinusoidal waves?

  3. For a sinusoidal waveform, the RMS value of current will be _______ times the maximum value of current.

  4. Which of the following factor have value of 1.1 for sinusoidal alternating current only?

  5. Which of the following factors indicates that wave departs from a sinusoidal condition?

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