Which quantity is used to compare AC heating to DC heating?

Which quantity is used to compare AC heating to DC heating?

• A. RMS
• B. Peak
• C. Average
• D. Frequency

Answer: (A)

The key idea is that heat in a resistor depends on the square of the current at every moment, so you need a single value that represents that heating effect over time. The root-mean-square (RMS) value does exactly that: it converts a time-varying AC current (or voltage) into an equivalent constant DC value that would produce the same average heating in a resistor. Using the RMS value lets you compare AC heating to DC heating with P = I^2R or P = V^2/R, using the same current or voltage level. Peak describes the maximum instantaneous current, which doesn’t reflect the average heating over a cycle. Average of the current isn't useful here because, for AC, it can be zero even while heating is happening. Frequency doesn’t determine how much heat is produced, only how fast the cycles occur.

The key idea is that heat in a resistor depends on the square of the current at every moment, so you need a single value that represents that heating effect over time. The root-mean-square (RMS) value does exactly that: it converts a time-varying AC current (or voltage) into an equivalent constant DC value that would produce the same average heating in a resistor. Using the RMS value lets you compare AC heating to DC heating with P = I^2R or P = V^2/R, using the same current or voltage level.

Peak describes the maximum instantaneous current, which doesn’t reflect the average heating over a cycle. Average of the current isn't useful here because, for AC, it can be zero even while heating is happening. Frequency doesn’t determine how much heat is produced, only how fast the cycles occur.