Question

How many plane mirrors are used in making a periscope? How are they arranged in relation to each other?
A. Two, perpendicular to each other
B. Four, parallel to each other
C. Four, perpendicular to each other
D. Two, parallel to each other

Answer 1

Hint: A periscope is a device used for observing over, around an object or through an obstacle. In short it is making a condition that prevents the direct line-of-sight from the observer's eye position.

Complete step by step solution:

Let us take a wide look at what a periscope is. A periscope is a device which prevents the direct sight of an observing object and makes the vision possible through any obstacle or object. A periscope is an instrument which includes two mirrors or reflecting prisms to vary the direction of the light coming from the sight which is being observed. In this case the first mirror deflects the light down through a vertical tube, the second one diverts it in a horizontal way so that the sight can be viewed more perfectly. The simplest model of periscope is a tube in which at the ends are two mirrors which are parallel to each other but at an angle of 45° with the axis of tube. This device cannot produce any magnification and will not give any crossline image. The vision is limited because of the simple geometry of the tube. So here the two mirrors are getting aligned in a parallel manner.

So the answer is option D.

Note: As the tube of periscope is longer or narrower, field of view will be smaller enough. Periscopes of this model were used in World War II in its armoured vehicles as observation instruments for the commanders.