White light appears to split into seven colors when passed through a prism or when refracted through water droplets, as in a rainbow. This phenomenon is known as dispersion.
White light is not composed of a single wavelength or frequency but is actually a combination of many different wavelengths or frequencies. It consists of a range of colors that span the visible spectrum. When white light encounters a medium such as a prism or water droplets, it interacts with the medium and undergoes refraction, causing the different wavelengths to bend at different angles. This refraction causes the white light to disperse into its constituent colors.
The reason we see seven colors (red, orange, yellow, green, blue, indigo, and violet) is due to human perception and the historical cultural association with these specific colors. In reality, the visible spectrum is a continuous range of colors, with no clear boundaries between them. The division into seven colors is a simplification and a convention rather than a scientifically precise distinction.
So, when white light passes through a prism or encounters water droplets, the different colors comprising the white light are refracted at different angles, resulting in the apparent splitting of white light into a spectrum of colors.