Ans. PRISM
A prism is a transparent body haying three rectangular and two triangular surfaces.
Angle of Prism
The angle of the triangular surface opposite to its base is known as angle of prism.
In case of a triangular prism, the emergent ray is not parallel to the incident ray. It is deviated by the prism from its original path. The incident ray PE makes an angle of incidence i at point E and is refracted towards the normal N as EF. According to the law of refraction n = sin i/sin r.
The refracted ray EF makes an angle r inside the prism and travels to the other end of the prism. : Refraction through This ray emerges out from prism at point F making a triangular glass prfcm an angle e. Hence the emerging ray FS is not parallel to the incident ray EF but is deviated by an angle D which is called angle of deviation.