Visible light, which is also known as white light, travels in straight lines at a tremendous speed through the air. Though we don't always see them, it is made up of different colors. When it passes through a prism it slows down and bends or refracts. The colors then separate and can be seen; this is called dispersion.
A prism has a greater density than air. When a light wave hits a prism the optical density changes. The optical density is the measure of the speed of the light wave as it moves through different materials. A prism slows the light down. This exposes what white light is made of: the different colors.
When white light enters and leaves a prism its wavelength changes. Within white light there are seven colors and each color has a different wavelength. The angles of the refracted beams of light depend on the angle of the initial light wave entering the prism and the color's wavelength. The prism disperses the light into seven colors: red, orange, yellow, green, blue, indigo and violet. This is known as "ROYGBIV."
Color and Wavelengths
The violet beam has a lower wavelength than the red beam and this affects the angle of refraction. The violet beam will be furthest away from the red beam and the other colors will be in-between according to their wavelength. The violet beam will therefore bend the most and the red beam will bend the least.
Angle of Deviation
The difference in how much the angle of the beam has changed upon entering and leaving the prism is called the "angle of deviation." The dispersion of light is more apparent with a triangular prism. This is because the surfaces of the triangular prism are slanted allowing for the different wavelengths to hit the prism and leave the prism at different speeds.