Dispersion

Description of the Process Used to Take the Photographs

This photograph was very difficult to take. A triangular prism was set upright on a
cardboard box covered with white paper. The room was darkened and a flash light (white light)
was aimed at the prism until a (small) array of colors appeared on the white paper. The flash was
not used to take this photograph.

Physical Concepts and Principles Involved in the Image

The physical phenomena represented in this photograph is dispersion.
Dispersion is a relatively easy phenomena to explain.Basically, the velocity of light
inside of a material is dependent on the wavelength of that light. The longer wavelength,
the smaller the velocity (and the greater the index of refraction). As well, we previously learned that
the amount of refraction thatlight experiences in any material is dependent on the velocity of the
light ray; wavelengths moving at a faster velocity are refracted the most.

Thus, it seems logical that violet and blue light, with their smaller wavelengths, would be refracted the most, whereas red light with its large wavelength would be refracted the least. This would create a pattern dispersion that is nearly identical to that found in our photograph.

In our photograph, the red light can be seen the most clearly. It has not been refracted by very much and follows a straight line from the center of the prism. Beside the red there appears to be a hint of very pale orange and yellow which is refracted by a slightly greater amount. Finally, the last color to appear is a deep violet which has been refracted the most because of its angle with the crystal.

Historical Background of This Phenomenon

The study of dispersion has a lengthy history, and it is difficult to pinpoint its exact beginnings.

In the sixteenth century the correspondence of Thomas Harriot and Johannes Kepler delved deeply into why light could be dispersed through a rainbow. Other scientists at the time were also conducting similar experiments.

Until the last couple of centuries, Newton used dispersion of light as one of the main proponents to the wave theory. The true nature of this phenomena was not discovered until the wavelenth of light was analyzed more closely.