Here we will discuss why violet is at the bottommost position of the spectrum made by the light emerging out of the prism on a white screen. This post is all about the position of violet color in the spectrum band created by dispersion of light by a prism.
Why is violet at the bottom of the spectrum?
Isaac Newton through his experiment concluded that white light consists of seven prominent colors. White light after suffering dispersion in a prism gets dispersed among its 7 component colors (colored light rays). And when these colored rays come out of the second refracting surface of the prism and fall on a white screen a spectrum of colors (VIBGYOR) is created. The position of violet is at the bottommost of this spectrum.
Now, why does violet come at that bottom position?
Out of these 7 colors, the speed of violet is the least. As we know that the refractive index is inversely proportional to the speed, hence violet has the highest refractive index (RI) among all 7 colors. Refractive Index is an indicator of how much a light ray will refract or bend from its original direction. Violet has the highest refractive index and it refracts the most, making its deviation angle the largest among those of all 7 colors. Hence violet deviates the most from the direction of the incident ray and gets closest to the base of the prism. This is the reason why violet is at the bottom-most position of the spectrum.
Related or reference reading:
Dispersion of white light – what is that & why it happens?