Dispersion of White Light Through a Prism: Understanding the Colors That Emerge First

White light, when passed through a prism, undergoes dispersion—the separation of white light into its constituent colors. This phenomenon is rooted in the principles of refraction and the varying refractive indices of different colors within the visible spectrum. In this article, we delve into the fascinating process of how and why red is the first color to emerge from the prism.

What Happens When White Light Is Dispersion Through a Prism?

When white light passes through a prism, it is broken down into its component colors. This occurs due to the principle of refraction, where light is bent as it moves from one medium to another. Each color of the visible spectrum has a different wavelength, and the angle of refraction depends on the wavelength. Red light has the longest wavelength and travels the least angle of refraction, while violet light has the shortest wavelength and is bent the most.

Red: The First Color to Emerge

Among the visible spectrum, red is the color that emerges first from the prism. This occurs because red light has the lowest refractive index among all the colors, allowing it to pass through the prism with less deviation. Specifically, red light travels through the prism with the highest velocity. For a typical prism made of Borosilicate glass (like BK7), the refractive index for red light is 1.514. In comparison, the refractive index for violet light is 1.528. The refractive index is inversely proportional to the velocity of light, meaning that red light travels faster within the prism. Therefore, red emerges first as it experiences the least bend and has the longest wavelength.

Simultaneous Emergence of Colors

It's important to note that all colors will emerge simultaneously, but the sequencing of their appearance on a screen is determined by their respective wavelengths. When the refracted light is projected onto a screen, red light appears at the top while violet light appears at the bottom. This is due to the varying speeds of each color within the prism. Different colors travel different distances at their respective velocities, resulting in a gradient from red at the top to violet at the bottom.

Principles of Dispersion in the Prism

The dispersion of white light through a prism is governed by the principles of refraction and the material properties of the prism. The prism acts as a dispersive medium, meaning it alters the speed of light passing through it. For a standard prism, the order of colors from top to bottom on the screen when the light exits the prism is:

Red Orange Yellow Green Blue Indigo Violet

However, it's crucial to understand that this order on the screen reflects the sequence of colors as they emerge from the prism, not the order in which they appear to emerge. The reason behind this sequence is the varying velocities and refractive indices of the different colors in the prism, as previously discussed.

Some might wonder if any specific color can be considered to emerge first among all the colors simultaneously. Technically, since all colors are emerging at the same moment but at different angles due to their respective wavelengths and refractive indices, none of the colors can claim to be the first to emerge. They all emerge together, just in different positions on the screen due to the refraction angles.

In conclusion, the first color to emerge from a prism when white light is passed through it is red, primarily because it has the least deviation due to its lower refractive index and longest wavelength. Understanding this phenomenon not only enriches our knowledge of light and optics but also has practical applications in various fields such as photography, spectroscopy, and telecommunications.