Number of peaks in sinusoidal power curve is, (where f is the frequency of AC).

Explanation

In alternating current (AC), the current and voltage follow a sinusoidal pattern. The power in an AC circuit is proportional to the square of the current (or voltage), resulting in a frequency that is double that of the current or voltage. If the frequency of the AC is 'f', then the power curve will have a frequency of '2f', hence there will be two peaks for each cycle of the AC current or voltage. Therefore, the correct answer is 2f. This understanding helps in recognizing that options 'f' would imply only one peak per cycle, and '3f' or '4f' would suggest an incorrect number of peaks based on the sinusoidal nature of the AC power.