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Back to Practice Questions
ElectricalBasic Electrical
PrevNext

The form factor of sinusoidal alternating current is

A

1

B

0

C

11

D

15

Correct Answer

тЪЩя╕П TE тАв Technical Concept & PrincipleElectricalBasic Electrical
Option C

11

Quick Summary:

The form factor of an alternating current (or voltage) waveform is defined as the ratio of its Root Mean Square (RMS) value to its Average value. For a perfectly sinusoidal waveform, this ratio is a constant value approximately equal to 1.11.

тЪЩя╕ПTETechnical SolutionConcept & Principle
ЁЯТб Explanation

The form factor of an alternating current (or voltage) waveform is defined as the ratio of its Root Mean Square (RMS) value to its Average value. For a perfectly sinusoidal waveform, this ratio is a constant value approximately equal to 1.11.

ЁЯФв Key Formulas

Kf=IrmsIavgK_f = \frac{I_{rms}}{I_{avg}}KfтАЛ=IavgтАЛIrmsтАЛтАЛ тАФ Definition of Form Factor

Kf=╧А22тЙИ1.11K_f = \frac{\pi}{2\sqrt{2}} \approx 1.11KfтАЛ=22тАЛ╧АтАЛтЙИ1.11 тАФ Form factor for pure sine wave

тЪЩя╕П Working Principle

For a sine wave with peak value ImI_mImтАЛ, the RMS value is Irms=Im2тЙИ0.707ImI_{rms} = \frac{I_m}{\sqrt{2}} \approx 0.707 I_mIrmsтАЛ=2тАЛImтАЛтАЛтЙИ0.707ImтАЛ. The average value (over a half-cycle) is Iavg=2Im╧АтЙИ0.637ImI_{avg} = \frac{2 I_m}{\pi} \approx 0.637 I_mIavgтАЛ=╧А2ImтАЛтАЛтЙИ0.637ImтАЛ. Dividing the RMS value by the average value gives Im/22Im/╧А=╧А22тЙИ1.11\frac{I_m / \sqrt{2}}{2 I_m / \pi} = \frac{\pi}{2\sqrt{2}} \approx 1.112ImтАЛ/╧АImтАЛ/2тАЛтАЛ=22тАЛ╧АтАЛтЙИ1.11.

ЁЯУМ Key Points
  • тЦ╕

    Form factor indicates the shape of the waveform relative to its average.

  • тЦ╕

    It is a dimensionless quantity.

  • тЦ╕

    A value of 1.11 is specific only to sinusoidal waves.

  • тЦ╕

    For a square wave, the form factor is 1.0.

тЬЕ Advantages
  • тЦ╕

    Useful for calculating the peak or RMS value from average-reading instruments.

  • тЦ╕

    Serves as an indicator of waveform distortion.

тЭМ Disadvantages / Limitations
  • тЦ╕

    Only applicable to periodic waveforms.

  • тЦ╕

    Does not provide information regarding the frequency of the waveform.

ЁЯЫая╕П Applications / Uses
  • тЦ╕

    Calibration of AC measuring instruments.

  • тЦ╕

    Transformer design and core loss analysis.

ЁЯУД Additional Information
  • тЦ╕

    The form factor is crucial in instrument design because most moving-coil instruments measure the average value, but require scaling to display RMS values.

  • тЦ╕

    Option D (1.15) corresponds to the form factor of a triangular wave.

ЁЯУК Diagram / Illustration
Form Factor (Sinusoid)RMS ValueAverage Value= 1.11
тЬЕ

C is correct тАФ The form factor of a sinusoidal AC waveform is mathematically derived as ╧А22\frac{\pi}{2\sqrt{2}}22тАЛ╧АтАЛ, which evaluates to approximately 1.11.

Core Concepts Used
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Root Mean Square Value Average Value Waveform Analysis
ЁЯТб EXAM TIP

Remember: 1.11 for Sine waves, 1.0 for Square waves, and 1.15 for Triangular waves. This pattern is a frequent target for memory-based questions in electrical engineering exams.

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