Physics Demo Number: 057

Approximate Run Time: 5 min

Prism Spectrum of White Light and Subsequent Recombination of Colors to White Light with a Second Prism

 

Demo Description

One focuses an image of a slit on a wall.

One then blocks the white-light slit image with a prism.

Appropriate positioning of the prism produces a multi-colored dispersion spectrum.

A second appropriately positioned prism then leads to the disappearance of the colored spectrum and the “magical” reappearance of the mechanically blocked image of the slit on the first wall.

 

Scientific Principles

  • Dispersion of light may be accomplished with prisms and with gratings.

  • Dispersion of white light yields different ordering of its colors for prisms from the ordering  obtained with gratings.

 

Equipment

  • 2 plastic prisms

  • Lab jack prism table with wood base

  • Projector light assemblies

  • Black metal disc / slit sources

  • Transmission diffraction grating

Equipment Location

  • The two plastic prisms, the diffraction grating and the  Lab Jack prism table are in Kit (057) on [C-3-3].

  • A wood base resides on [C-3-3].

  • The first projector light source lives in a Kit on [C-1-4].

  • The second projector source resides  in  Kit (057) on [C-3-3].

  • Black metal disc- slit- source- assemblies live in  35mm slide trays mounted on the projectors.








Instructions

The first photo  above shows the two plastic prisms resting on a vertically suspended black prism table which in turn rests on a wood base.

A black metal disc with a slit (which is mounted in a white 35mm slide card ) acts as the slit source for  each of the respective projectors.

One focuses an image of the slit on a wall in the lecture hall and then blocks the white slit image with the first prism.

Appropriate rotation of the prism then produces the multi-colored dispersion spectrum of the white light on another wall.

Carefully placing the second prism on the black prism table in the correct position and orientation leads to the disappearance of the colored spectrum and the “magical” reappearance of the mechanically blocked image of the slit on the first wall.

The second photo shows alternate apparatus for the second light source ( the projector is considerably lighter to haul around ).

The third photo depicts the high quality transmission diffraction grating used for achieving dispersal of  white light into its spectral colors.

 

  
Writeup created by David A. Burba
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