Absorption

When light strikes an opaque material the wavelengths that are not reflected are absorbed and their energy is converted to heat (notice that absorption has a ‘p’).

  • When sunlight strikes an opaque object or material, it can be reflected or absorbed.
  • If light is reflected it bounces off at the same wavelength.
  • If light is absorbed, the short wavelength energy is changed to long wavelength (heat).
  • Of the light that reaches Earth’s surface from the sun:
    • 54% is already heat (infrared) before it reaches the earth’s atmosphere.
    • 45% is visible light.
    • 1% is shorter wavelengths (ultraviolet).
  • Absorption of a particular wavelength of light into a material takes place when the frequency of the wave matches the frequency at which electrons in the atoms of that material vibrate.
  • Because the electrons in different atoms and molecules have different frequencies they selectively absorb different frequencies of visible light.