Question

Why do you not see a spectrum of colours when light passes through a flat pane of glass?

Answer 1

When light passes through a flat pane of glass, the refracted light emerges out of the glass pane without any deviation because a glass pane has two sides that are parallel to each other. As the emergent light does not deviate from the original direction by any angle, we do not see the different colours of the light separated out in the form of a spectrum. Therefore, in order to view a spectrum of colours, the incident rays have to fall on an object whose surfaces are not parallel, such as a glass prism (triangular shape).