Ham Radio General Class Practice Test

Which value of an AC signal results in the same power dissipation as a DC voltage of the same value?

1. The peak-to-peak value

2. The peak value

3. The RMS value

4. The reciprocal of the RMS value

The correct answer is: The RMS value

The RMS (Root Mean Square) value of an AC signal is the correct answer because it represents the effective value of an alternating current that produces the same amount of heat (or power dissipation) in a resistor as a corresponding DC voltage of the same value. When evaluating AC signals, the RMS value is particularly significant because it accounts for the varying nature of AC voltages over time. Unlike DC voltage, which maintains a constant level, AC voltage fluctuates between positive and negative values. The RMS calculation takes this fluctuation into consideration by averaging the power delivered efficiently over time. For example, for a sinusoidal AC voltage, the RMS value is approximately 0.707 times the peak value. This is important because if you were to use the peak value of an AC signal to compare to a DC signal, you would not get an accurate representation of how much power is dissipated in a resistive load. In contrast, peak-to-peak values represent the total swing of the waveform and do not provide a meaningful correlation to the average power usage, while the reciprocal of the RMS value lacks a direct relationship to actual power dissipation. Therefore, the RMS value is crucial for ensuring that power comparisons between AC and DC systems are valid and meaningful.