Final answer:
In the SI system, the frequency of electromagnetic radiation is measured in hertz (Hz).
Step-by-step explanation:
In the SI system, the frequency of electromagnetic radiation is measured in hertz (Hz). The frequency of a wave represents how many wave cycles pass a point in one second. It is important to note that the frequency and wavelength of electromagnetic radiation are inversely proportional, meaning that as the frequency increases, the wavelength decreases.