Which type of radiation has the longest wavelengths and lowest energies?

• A. Ultraviolet
• B. Gamma rays
• C. Radio waves and microwaves
• D. Visible light

Answer: (C)

Long wavelengths mean low energy per photon. In electromagnetic radiation, energy depends on frequency (E = h f), and frequency is inversely related to wavelength (f = c/λ). So longer wavelength gives smaller energy per photon (E = h c / λ).

Among common types listed, radio waves have the longest wavelengths, with microwaves also having very long wavelengths. This combination results in the lowest photon energies compared with visible light, ultraviolet, infrared, X-rays, and gamma rays. Gamma rays and ultraviolet have much shorter wavelengths and higher energies, while visible light is in between.

So radio waves and microwaves are the ones with the longest wavelengths and the lowest energies among the options.