Question

You are given a disc divided into seven sectors with colors violet, indigo, blue, green, yellow, orange and red in them. What would be its color when it is rotated rapidly?

Answer 1

You know what happens, when a light ray passes through a prism and it gets refracted to produce a sequence of colors. In this scenario, a disc with multiple colors is given and asks what happened when it is combined into one.

Complete step by step solution:
Newton initially used a prism to understand the nature of white light when it passes through 2 different mediums. He later understood that the light ray made up of one color, passes through the second medium, and comes out back dispersing 7 different colors. This is also a similar concept on how the rainbow is formed. The dispersion experiment was easy to perform and understand.
However, Newton wanted to check whether all 7 colors coming out of the prism recombined back as white light or not. For this purpose, he constructed a disc, which was divided into seven segments equally and was painted with the colors he witnessed when the white light is dispersed.
When this disc is rotated at very high speed, the colors begin to combine to produce white screen on the disc. The disc appeared white as the colors began to undergo temporal optical mixing, where light reflected off the color, began to mix in equal proportions, thus producing white light.

Note:
The same experiment can also be performed using another prism. This is called a two prism experiment. The second prism is kept in the opposite orientation as the first one to facilitate the inversion. When the VIBGYOR is passed to the second prism as incident ray of varied angle, the rays of color begin to converge at the point of refraction after undergoing a series of deviations, thus coming out back as white light.