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Circuit and electromagnetism basics

Which is closest to the peak value (amplitude) of a sinusoidal AC voltage with an RMS value of 100 V?

  1. AAbout 141 V
  2. B100 V
  3. CAbout 71 V
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Answer: A. About 141 V

For a sine wave the RMS value is 1/√2 times the peak, so the peak is √2 times the RMS value: 100 V × √2 ≈ 141 V (141.4 V). The RMS value is the DC voltage that would dissipate the same power in the same resistor; AC voltmeter readings and nominal mains voltages (such as 100 V) are RMS values. The peak-to-peak value is about 283 V, so component voltage ratings must be judged against the peak, not the RMS value.

  • A. Correct. 100 V × √2 ≈ 141 V.
  • B. 100 V is the RMS value itself, not the peak.
  • C. About 71 V is the RMS value divided by √2—the conversion in the wrong direction.
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