In a prism, why does the emergent ray always bends towards the base of the prism???
When a ray of light passing through a rarer to a denser medium the refracted ray bends towards the normal,the the angle of refraction will be less than the angle of incidence.But when a ray light passing through a denser to a rarer medium( from glass to air) the refracted ray bends away from the normal,then the angle of emergence will be greater than the angle of incidence in the second face of the prism
In the prism the ray of light is emerging out through the second face that is from glass to air.Hence the emergent ray bends away from the normal -that is bends towards the base of the prism.
When they?re parallel, as with a plane sheet of glass, the emergent ray is bent back to be parallel to the incident ray. When they?re not parallel however, consider an emergent ray orthogonal to the exit interface. It cannot also be orthogonal to the entry interface, and therefore the incident ray will be bent away from the internal ray, i.e. towards the base, assuming as usual that the refractive index is higher inside the prism than outside.
So, it needs more space to scatter itself and if another prism kept upside down those seven colours meet the base of first prism and again emerges to single light (white light) and continues its path