Dispersion of Light — Definition
Definition
Imagine a beam of ordinary white light, like sunlight, traveling through the air. It appears uniform and colorless. Now, picture this beam entering a triangular piece of glass called a prism. What happens next is quite fascinating: the single beam of white light doesn't just bend (refract) once, but it actually spreads out and separates into a beautiful band of colors, much like a rainbow.
This spectacular splitting of white light into its individual color components is what we call the 'dispersion of light'.
Why does this happen? The key lies in understanding that white light isn't a single color; it's a mixture of several colors, specifically the colors of the rainbow: Violet, Indigo, Blue, Green, Yellow, Orange, and Red (VIBGYOR).
Each of these colors corresponds to a different wavelength of light. When light passes from one medium (like air) to another (like glass), it bends. This bending is governed by a property called the refractive index of the medium.
Crucially, for most transparent materials, the refractive index is not the same for all colors of light. It varies slightly with the wavelength of light.
Specifically, for visible light, the refractive index of a medium is generally higher for shorter wavelengths (like violet light) and lower for longer wavelengths (like red light). This means that violet light, having a shorter wavelength, slows down more and bends more significantly when it enters and exits the prism compared to red light, which has a longer wavelength and bends less. The other colors bend by intermediate amounts, in their respective order.
As a result of these differing degrees of bending, or 'deviation', the various colors that were initially combined in the white light beam get separated from each other. Violet light deviates the most, and red light deviates the least.
This angular separation creates the visible spectrum, where we can clearly distinguish the distinct colors. This phenomenon is not just a laboratory curiosity; it's responsible for the vibrant colors of a rainbow after rainfall, where tiny water droplets act like miniature prisms, dispersing sunlight into its constituent hues.