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Refraction of Light Through a Glass Prism
A glass prism has two triangular bases and three rectangular lateral surfaces inclined to each other at an angle called the angle of the prism ($A$). When a ray of light enters the prism from air, it goes from a rarer medium to a denser medium and bends towards the normal. Path of Light: The incident ray $PE$ strikes the surface $AB$ of the prism and bends towards the normal as refracted ray $EF$. Inside the prism, it travels to surface $AC$ and emerges out into the air (denser to rarer medium), bending away from the normal along the path $FS$. Here, $PE$ is the incident ray, $EF$ is the refracted ray, and $FS$ is the emergent ray. Angle of Deviation Definition: The angle between the direction of the incident ray and the emergent ray is called the Angle of Deviation ($\angle D$ or $\delta$). Explanation: Because of the two refractions at the surfaces of the prism, the emergent ray is bent at an angle to the direction of the incident ray. The magnitude of this deviation depends on the angle of the prism, the angle of incidence, and the refractive index of the prism material. Dispersion of White Light Definition: The splitting of white light into its component seven colours when passing through a transparent medium like a glass prism is called dispersion. Spectrum: The band of the coloured components of a light beam is called a spectrum (VIBGYOR: Violet, Indigo, Blue, Green, Yellow, Orange, Red). Cause of Dispersion: White light consists of seven different colours, each having a different wavelength and frequency. Light of different colours travels at different speeds through a glass prism. According to Snell's law, the refractive index of a medium depends on the wavelength of light. Violet light has the shortest wavelength and experiences the maximum refractive index and hence maximum deviation, whereas red light has the longest wavelength, experiencing minimum deviation and bending the least. Consequently, each colour emerges along a slightly different path, resulting in the distinct band of colours known as a spectrum.