Question

Diagrams (a) and (b) in figure below show the refraction of a ray of light of single colour through a prism and a parallel sided glass slab respectively.

1. In each diagram, label the incident, refracted, emergent rays and the angle of deviation.
2. In what way the direction of emergent ray in the two cases differ with respect to the incident ray? Explain your answer.

Answer 1

1. 1. AB stands for the incident ray. BC stands for a refracted ray. CD stands for emergent radiation. The angle of deviation is ∠EOD, where the incident ray produced forward meets the emerging ray produced backward.

   2. AO stands for incident radiation. OB stands for a refracted ray. BC stands for the emerging ray. There is no angle of deviation, since the incident ray in a glass block is parallel to the emergent ray.
      

2. In the glass prism, the incident beam AB would have gone along ABEF in the absence of the prism. It seems that the emergent ray CD is progressing ECD. Thus, the ray AB has been deviated through ∠FED = δ along CD.

   In the slab of glass, emergent ray CD emerges in a rare medium, deviates from the normal, and is parallel to incident ray AB.