A periscope is an instrument which helps in viewing the objects which are not in the line of sight of the observer. It is used by the submarines to look at objects above the water surface.

The principle behind periscope is reflection between two parallel plane mirrors. It consists of long cylindrical hollow tube bent at right angles and two plane mirrors are kept parallel and facing each other. The mirror is fixed at 45 degrees with the framework at the top and the bottom of the tube.

Let see the simple structure of periscope –

We use two mirrors in a simple periscope.