Rayleigh scattering occurs under which condition?

• A. Targets are much smaller than the wavelength
• B. Targets are larger than the wavelength
• C. It occurs only in air
• D. It is a form of refraction

Answer: (A)

Rayleigh scattering happens when the scatterers are much smaller than the wavelength of the light. In this regime, the particles act like tiny dipoles that radiate energy, and the amount of light scattered depends very strongly on wavelength—roughly increasing as the inverse fourth power of the wavelength. That means shorter wavelengths (blue/violet) scatter much more than longer wavelengths (red), which is why the sky looks blue most of the time. If the particles are not much smaller than the wavelength, another scattering regime (Mie scattering) takes over, with a much weaker dependence on wavelength. This is a scattering phenomenon, not refraction, and it can occur in many media, not just air.