6F10.30 - Recombining the Spectrum - Prisms

Code Number:
Demo Title:
Recombining the Spectrum - Prisms
Splitting White Light, Recombining the Spectrum
Area of Study:
4 prisms, slide projector with slit slide, tracing paper screen.

Place the slit slide into the slide projector. Direct the light from the projector into a prism and observe the spectrum on the screen.  Use three other prisms in the configuration shown to recombine the spectrum.

A common fallacy is that it only take two prisms to do the recombination experiment.  However, if you do this and look closely at the recombined light bar you will see that the edges are red on one side and blue on the other.  This is due to the fact that the light rays coming out of the first prism are spreading out, and therefore the second prism is only able to recombine the central portions of the spectrum.  The two extra prisms are essentially used to take the spreading rays and make them parallel, and then take the parallel rays and refocus them before going into the final prism.

  • Tommaso Rosi, Pasquale Onorato, Luigi Gratton, and Stefano Oss, "Color Mixing with Four Prisms Redux", TPT, Vol. 56, #7, Oct. 2018, p. 421. 
  • Kirk McDonald, "Recombining Rainbows", TPT, Vol. 56, #4, Apr. 2018, p. 196. 
  • Rafael Garcia-Molina, Lejandro Mazo, and Santiago Velasco, "A Simple Experiment Setup to Clearly Show thatLight Does Not Recombine After Passing Through Two Prisms", TPT, Vol. 56, #1, Jan. 2018, p.14.
  • Jukka O. Mattila, "Spectral Experiments with White Light", TPT, Vol. 32, #6, Sept. 1994, p. 338.
  • Thomas B. Greenslade, Jr., "Spectrum Recombination", TPT, Vol. 22, #2, Feb. 1984, p. 105.
  • Fred T. Pregger, "Recombination of Spectral Colors", TPT, Vol. 20, #6, Sept. 1982, p. 403.
  • Dudley H. Towne, "Teaching Newton's Color Theory Firsthand", AJP, Vol. 61, #2, Feb. 1993, p. 113.
  • Frank S. Crawford, "Variations on a Famous White-Light Experiment of Isaac Newton", AJP, Vol. 39, #12, Dec. 1971, p. 1538.
  • T. D. Rossing and C. J. Chiaverina, "4.3, Dispersion", Light Science - Physics and the Visual Arts, p. 82.
  • C. P. Jargodzki, Franklin Potter, "58, Prisms", Mad About Physics - Braintwisters, Paradoxes, and Curiosities", p. 19.
  • Robert L. Wild, "164, Grating Recombination of an Image", Low-Cost Physics Demonstrations, p. 94.
  • "#12, Combination of Colors to Form White Light", Experiments in Optics, J. Klinger Scientific Apparatus, Bulletin 101, p. 14.

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