Hippolyte Marié-Davy first discovered the instrument, the periscope, for naval purposes during the second half of the nineteenth century. The word periscope has arrived from the association of two words, "peri" and "scope", where peri means "around" and scope means "viewing instrument". However, during the 15th century, it is said that Johannes Gutenberg, has invented the periscope in order to look above people's heads during a parade. Later this technique was applied for better navigation in submarines.

Definition of Periscope

A periscope is defined as an optical apparatus that basically follows the shape of a tube, and which has a set of prisms or mirrors. The observers to see behind high obstructions that are faced by the observer use them. In simpler terms, one can use this apparatus to see things that are basically out of sight.

The submarines earlier extensively used this instrument so that they can see things that are out of their vision, which means that they are on the surface of the sea (, 2022). However, this apparatus makes use of the principles of ''Laws of Reflection''.

Parts of Periscope

A periscope is developed by some vital parts that consist of a tube, prisms, a set of mirrors, lenses, and an eyepiece. The tube forms a ''Z'' shape and at one end there lies the eyepiece, through which the observer will look through. Two plane mirrors are used that are placed at an angle of 45o and they are set in a parallel way to the other place of the existing mirror.

Principles followed by periscope


Figure 1: Periscope

The apparatus of the periscope follows the ''Laws of Reflection''. In simpler terms, as the ray of light enters the tube it falls on the mirror that is placed at an angle of 45o .

After which the light is reflected by the other mirror that is placed on the other corner of the tube at 45o angles. Following this, the ray of light enters the sight of the observer. However, the light ray gets reflected two times before reaching the eye of the observer. The working of the periscope is displayed in the above-given image in figure 1.

It is to be noted that the image that is formed in the plane mirror displays the characteristics of an image as ''laterally inverted'' and ''virtual'' in nature (, 2022). When again the image gets reflected in the second mirror then the image does not display lateral inversion.

Three Laws of Reflection

Laws of reflection

Figure 2: Laws of Reflection

''Laws of reflection'' is quite viral when talking about periscopes, but however, one needs to know about the phenomenon of reflection. The phenomenon of reflection is defined when a light ray falls on the mirror, then the light does not get absorbed in the medium of the mirror and radiates the light, which is known as the incident ray. However, the light when reflected back is termed a reflected ray. Regular and irregular reflections are crucial in understanding the idea of the laws of reflections (, 2022).

A regular reflection occur when the light ray falls on a smooth surface and forms a clear image, on the other hand, the irregular reflection is defined as when the light ray falls on a rough surface.

In simple terms, the ''laws of reflection'' states that, when a light ray falls on the plane surface of the mirror, the ''incident ray'', the ''reflected ray'' and the ''normal'' lie on the same plane (, 2022).

This in turn states that the angle of incidence ray to the normal is equal to the angle of the reflected rays with the normal drawn at the point of intersection of reflection.

What is the difference between a periscope and a telescope?

  • There is a vast difference between the telescope and periscope, however, the difference is that a telescope is an optical apparatus that is monocular in nature and supports magnification of the images that lie far from the observer, at a distant place. However, the application telescope is seen in the field of astronomy (, 2022).

  • On the other hand, a periscope is used to see objects at different heights. With the application of the periscope, the observers are allowed to view images that are majorly out of sight. However, periscopes are used in submarines to see the objects present on the surface level of the sea and oceans.

Applications of periscope

  • There are various applications that are found in the usages of periscopes; however, they are majorly used in submarines. In the aspect of threat detection, the application of the periscope is evident, as it helps in determining the distance of the torpedo. It allows one to be out of sight and supports the observers to hide and can be used for military purposes.

  • However, it is also applied in the field of nuclear reactors, which supports observing the chemical reactions. In addition to these, the periscope is also used in armoured vehicles and in tanks in order to inspect the surroundings (, 2022).

  • It can be said that usage s of periscopes is evident in the fields of medicines, military and submarines.

    applications of periscope

Figure 3: Applications of periscope


In this lecture notes, we find an extensive study about the periscopes. Although the periscope was invented long back ago, analyzing the principles that are followed by the periscope is the basic ''Laws of Reflection''. This signifies the basic rule for reflection, where the angle is equal to the angle of reflection and the angle of incidence. This allows the image to reach the viewer easily, however, due to the presence of two plane mirrors, the images change from inversion to the formation of erect images. Several benefits are noticed with the application of periscopes as it is highly used in the battlefield and medicinal fields, as its advanced stage is known as the technology of endoscopy.


Q1. Why is the structure of the periscope ''Z shaped''?

The structure of the periscope is "Z shaped" as it supports seeing the objects that are at a certain height. In addition to this, the light ray that enters needs to get reflected in the other mirror, so that the viewer can see the image. For this reason, only the periscope displays a "Z shaped".

Q2. How in the field of medicine are periscopes used?

The periscopes are used in the medicinal fields, as they assist in several diagnostic techniques. Furthermore, it is used as a part of methods that are less obtrusive in nature.

Q3. What types of mirrors are used in periscopes and floodlights?

The types of mirrors used in periscopes are plane mirrors and the types of mirrors used in floodlights are concave mirrors.

Q4. What property is used in periscopes?

The property that is followed by the periscopes is the phenomenon of reflection. Through the reflection of images, it is quite difficult to get a view that is out of the sight of the observers.


Websites, (2022), Laws Of Reflection, Retrieved from: [Retrieved on: 7th June 2022], (2022), Formation of Periscope, Retrieved from: [Retrieved on: 7th June 2022], (2022), Retrieved from: [Retrieved on, 7th June 2022], (2022), Mirrors used in Periscope, Retrieved from: [Retrieved on: 7th June 2022]


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Updated on: 18-Aug-2023


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