If the mirror of a periscope is replaced by lenses then which of the following phenomenon will occur to operate the periscope properly?

Option 3 : Total internal reflection

Concept:

Periscope:  

• An optical instrument which is used for observing through an object which is prevented by direct line of sight is called as a Periscope.
• There are two mirrors in the periscope which are placed at an angle of 45°.
• When the light falls on one of the mirrors then after reflection from first mirror it fall on second mirror which further reflect it and fall on the eye of the observer.

Explanation:

• As due to mirrors there is reflection of light from one mirror to other and finally fall on the eye of the observer
• When we replace it with the lenses then there must be a refraction of light so that then can go to other lens and finally on observer.
• The phenomenon of reflection of light by a lens is called as total internal reflection.  Hence option 3 is correct.