Which electromagnetic waves have the longest wavelengths?

• A. Gamma rays
• B. X-rays
• C. Infrared waves
• D. Radio waves

Answer: (D)

Radio waves have the longest wavelengths in the electromagnetic spectrum. Wavelength is a key property of electromagnetic waves and is inversely related to frequency; that is, as the wavelength increases, the frequency decreases. Radio waves can have wavelengths that range from about one millimeter to several kilometers, which is much longer than that of gamma rays, X-rays, or infrared waves.

Gamma rays have very short wavelengths, typically less than 0.01 nanometers, while X-rays range from about 0.01 to 10 nanometers. Infrared waves, which sit just beyond the visible spectrum, have wavelengths ranging from about 700 nanometers to 1 millimeter. In contrast, radio waves, being at the lower end of the electromagnetic spectrum, encompass a much broader range of longer wavelengths, making them ideal for applications like communication and broadcasting. Thus, among the options provided, radio waves clearly exhibit the longest wavelengths.