What does frequency refer to?

• A. The distance between successive peaks in a wave.
• B. The number of cycles per unit time of a wave, measured in hertz.
• C. The energy per photon.
• D. The amplitude of the oscillation.

Answer: (B)

Frequency tells you how often a wave repeats its pattern in one second. It’s the number of cycles per unit time and is measured in hertz (Hz). If you observe a fixed point and count how many peaks pass by each second, that count is the frequency. This is related to the wave’s period by f = 1/T, where T is the time for one complete cycle. It’s different from the distance between peaks, which is the wavelength, and from the amplitude, which describes how tall the wave is. In electromagnetic waves, higher frequency also means higher energy per photon (E = h f), tying frequency to energy even though frequency itself is simply about how often the wave repeats.