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Circuit and electromagnetism basics

When a sinusoidal AC voltage of 100 V RMS is applied to a 50 Ω resistor, what is the average power dissipated?

  1. A100 W
  2. B400 W
  3. C200 W
Show answer and explanation

Answer: C. 200 W

Using RMS values, average AC power is calculated with the same formulas as DC: P = V²/R = 100²/50 = 10000/50 = 200 W. Using the peak value (about 141 V) instead gives 141²/50 ≈ 400 W, twice the correct value. The instantaneous power swings between 0 and a maximum of 400 W at twice the supply frequency, averaging 200 W.

  • A. 100 W uses about 70.7 V, the RMS value divided by √2 once more.
  • B. 400 W uses the peak value and equals the maximum instantaneous power.
  • C. Correct. 100²/50 = 200 W.
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