Question

Name the instrument where this action of prism is put into use.

Answer 1

Hint: Here to find the use of the instrument as mentioned in the diagram you should look for the deviation and property of the ray after a ray passes through the prism and it’s possible geometry to speculate about its uses.

Complete step by step answer:
As we can see from the diagram given in the question incident ray is deviated by right angle now if we put another prism beside surface BC then it will again be deviated by right angle
So total deviation by both prisms will be 180 degrees which is identical to plane mirrors which we use in everyday life .So this action of prisms can be used in all places where we use plane mirrors but due to other factors like cost of production, ease of use we don’t use it everywhere.

Mostly it is used in devices like periscope.

The major advantage of using prisms in periscope rather than plane mirror is
1. It does not require silvering.
2. The reflection of light is 100% it means no energy is lost in reflection which is of great use when we try to see objects where there is a low availability of light. If we use mirrors in such places a large part of energy will be lost which will give us a low quality image.
3. Multiple reflections do not take place in a reflecting prism as compared to plane mirrors. Due to this, only one image is formed, which is very bright and clear.
4. A reflecting prism is free from the trouble arising out of vanishing of the silvering of mirrors with the passage of time.

Note: One prism deviates the light ray by right angel so if we add another prism in the path of the deviated ray it will again be deviated by the right angle and the total deviation will be equal to the linear angle which is same as angle deviated by a plane mirror so this prism can be put into use wherever we need a plane mirror.