School of Mathematics and Natural Sciences

Color through Absorption of Light



Either Ethanol - DANGER

H225, H319
P210, P240, P305+P351+P338, P403+P233

or Acetone - DANGER

H225, H319, H336, EUH066
P210, P240, P305+P351+P338, P403+P233

A flat cuvette is filled about half with green leaf extract in ethanol or acetone. Dark strips of tape are adhered to the cuvette, leaving just chink of light open (a slit diaphragm in front of the cuvette can be used instead). The flat cuvette is places into the beam path of a projector (a white LED flash light can be used instead). After transitioning through the solution the slip of light is broken up with the help of a prism or a diffraction grating into its spectral colors, which are projected onto a screen. This approach enables the observation of the colors that are absorbed in the solution.

  • The spectrum of the white light emitted by the lamp contains all colors of the rainbow. Contrary to this the spectrum of the light that has transitioned through the solution is missing colors, showing up as dark areas on the screen: One area in the blue-violet range and one in the red range of the visible spectrum.

The following extra experiments can be recommended:

  • The experiment described above can be done with other colored solutions, in order to examine which color ranges of the spectrum will appear as dark areas.
  • Absorption spectra of the solutions can be recorded using a photometer. Through this it can be determined that the dark areas from the spectrums match the maxima in the graph depicting the absorption of the solution.
  • In a slightly darkened room (curtains suffice) objects of various colors are observed in different colored lights from LED flash lights e.g. toy blocks, fabrics of fruits. Objects that colors are known in day light appear inpart in different colors.

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