To understand the behaviour of light when it isincident on the plane of a prism and passes into the prism, we need to define certain terms associated with prismsYou might have seen a rainbow form in the sky just after a rain shower.It must have fascinated you with spectacular colours appearing as a semicircular band of colours.
• How could the white light of the sun give us various colours of the rainbow?
In previous chapters, you have studied the behaviour of light when it refracts through plane surface and curved surfaces, such as a lens. You also studied the nature, position and relative size of image formed by lenses.
• What happens to a light ray when it passes through a transparent medium bounded by plane surfaces which are inclined to each other?
• What is a prism?
PrismA prism is a transparent medium separated from the surrounding medium by at least two plane surfaces which are inclined at a certain angle in
such a way that, light incident on one of the plane surfaces emerges from the other plane surface.To understand the behaviour of light when it isincident on the plane of a prism and passes into the prism, we need to define certain terms associated with prisms
Consider a triangular glass prism. It contains two triangular bases and three rectangular plane lateral surfaces. These lateral surfaces are inclined to each other
Let us consider that triangle PQR represents outline of the prism where it rests on its triangular base. Let us assume that a light ray is incident on the plane surface PQ of a prism at M as shown in figure 7. Draw a perpendicular to the surface at M. It becomes a normal to that surface. The angle between the incident ray and normal is called angle of incidence (i1). The ray is refracted at M. It moves through prism and meets the other plane surface at N and finally comes out of the prism. The ray which comes out of the surface PR at N is called emergent ra. Draw a perpendicular to PR at point N. The angle between the emergent ray and normal is called angle of emergence (i2 ).The angle between the plane surfaces PQ and PR is called the angle of the prism or refracting angle of prism A and the angle between the incident ray and emergent ray is called angle of deviation(d).