Question

The working principle of a periscope is ________

Answer 1

Hint: A simple periscope is an optical device that is used to see objects at a different height level that may not be possible to observe due to obstacles in the way. It works on the principle of simple reflection. Light from the object is reflected by a series of mirrors inclined at a certain angle which allows it to reach the observer bypassing obstacles that may have been present in a straight line path from the object to the observer.

Complete step by step answer:
A simple periscope is an optical device that is used to observe objects that may be at a different height level or have obstacles in the straight line sight of the observer and the object.
A simple periscope works upon the principle of reflection by a mirror. Mirrors are set up such that the angle of incidence of the light ray is ${45}^0$. Now since, according to the laws of reflection, the angle of incidence is equal to the angle of reflection, the angle of reflection will also be ${45}^0$. Hence, the light ray will effectively be turned by $({45}^0+{45}^0={90}^0)$. Hence, by a series of such ${90}^0$ turns of light with the help of properly oriented mirrors, the object can be observed by the observer.
This will be clear with the help of the following diagram.

In the above figure, light rays from the object enter the periscope and are turned by ${90}^0$ by a mirror. A second mirror again turns it back by ${90}^0$ and the light ray reaches the eye of the observer and hence, the observer is able to observe the object at a different height level.
This concept is used especially in submarines, where periscopes are used to observe objects above the sea level while the submarine itself remains below the water.

Note: Simple periscopes work upon the principle of reflection. However there are some modern complex periscopes that have been developed that use total reflecting or refracting prisms instead of mirrors. Hence, some complex periscopes also rely upon the principle of refraction for their functioning. Other complex periscopes also employ optical fibres that function and carry light using the principle of total internal reflection of light inside a fibre.
Therefore, students must know of these periscopes also. However, in essence, all of them, like simple periscopes, have an element of reflection and are dependent on the principle of reflection for their functioning.