6F10.30 - Recombining the Spectrum - Prisms

Code Number:
6F10.30
Demo Title:
Recombining the Spectrum - Prisms
Condition:
Excellent
Principle:
Splitting White Light, Recombining the Spectrum
Area of Study:
Optics

Disclaimer

Equipment:
4 prisms, slide projector with slit slide, tracing paper screen.
Procedure:

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.

References:
  • 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.

Disclaimer: These demonstrations are provided only for illustrative use by persons affiliated with The University of Iowa and only under the direction of a trained instructor or physicist.  The University of Iowa is not responsible for demonstrations performed by those using their own equipment or who choose to use this reference material for their own purpose.  The demonstrations included here are within the public domain and can be found in materials contained in libraries, bookstores, and through electronic sources.  Performing all or any portion of any of these demonstrations, with or without revisions not depicted here entails inherent risks.  These risks include, without limitation, bodily injury (and possibly death), including risks to health that may be temporary or permanent and that may exacerbate a pre-existing medical condition; and property loss or damage.  Anyone performing any part of these demonstrations, even with revisions, knowingly and voluntarily assumes all risks associated with them.