Skip to main content

WHAT IS DOUBLE REFRACTION ? WHAT IS NICOL PRISM? WHAT IS THE FUNCTION OF NICOL PRISM? WHAT IS THE CONSTRUCTION OF IT?

 Before knowing about double refraction, we need to understand refraction. So, refraction is the bending of light rays when it passes from one medium to another medium due to the different optical densities of the medium.

   To measure the optical density, a refractive index is used. The Refractive index of a medium may be defined as the ratio of the speed of light in a vacuum or air to the speed of light in that medium.

There are two cases obtained: 

1) if the incident angle and the angle refraction are zero and the refractive index of the first medium is not equal to the refractive index of the second medium, then the lights are not refracted.

2) If the refractive index of the first medium is equal to the refractive index of the second medium, then also the lights are not refracted.

Refraction follows some rules: 

1) The incident ray, refracted ray, and the normal at the point of incidence all lie in the same plane. 

2) The relation between the incident and refraction angle and the refractive indices of the medium, which is known as snell's law.

   It states that the ratio of the sine of the angle of incidence to the sine of the angle of refraction is equal to the refractive index of the second medium with respect to the first medium.



When an unpolarized light (vibrates all directions) strikes on a doubly refracting crystal-like calcite, quartz, etc. the unpolarized light splits into two refracted rays. One ray is called the “O” ray and the other is the “E” ray and this phenomenon is called double refraction. Both “O” and “E” rays are plane-polarized lights but, their direction of vibration of the electric field is different. The electric field of the “E” ray vibrates in the direction of the plane of the paper and the electric field of the “O” ray vibrates in the perpendicular direction of the plane of the paper.

NICOL PRISM

Nicol's prism is invented by William Nicol in the year 1828. It is an optical device, which is made from calcite crystal and is used in many optical instruments for producing and analyzing plane-polarized light.

      It is worked in the principle of double refraction.

After the phenomena of double refraction, the two refracted rays produce under the Nicol Prism one is the “O” ray, and another one is the “E” ray. The “O” rays obey the laws of refraction as well as laws of reflection but “E” rays do not follow any laws. Hence, the “O” rays are eliminated from the Nicol Prism due to total internal reflection phenomena and only “E” rays come out from the Nicol Prism. In this way, plane-polarized light in the direction of the plane of paper is produced from the Nicol Prism. 


Construction of Nicol Prism: 



It is constructed from the calcite crystal. At first, calcite crystal cuts into two prism shapes and connected them together with the help of a special type of cement, which is known as Canada balsam. It is a transparent material, which has a refractive index is about 1.55. Finally, the shape of the calcite crystal is Rhombohedral that means the angles P, Q, R, S are 112, 68, 112, and 68 degrees respectively as shown in the figure. The length of the Nicol prism is 3 times greater than its thickness.

   When unpolarized lights come and hit the Nicol prism, the lights split into two refracted rays. One ray is known as the “O” ray and the other is the “E” ray and this phenomenon is called double refraction. Both “O” and “E” rays are plane-polarized lights but, their direction of vibration of the electric field is different.

Comments

Post a Comment

Popular posts from this blog

What are the tectonic plates? How they are formed?

 Before knowing about the plate tectonic theory, we need to know the meaning of the plate and tectonic. So, the plates are the parts of the lithosphere and they are formed due to Exogenetic force and Endogenetic force. These forces were acting on the lithosphere continuously and broke it into 27 parts ( 7 are major and 20 are minor ) and each part of the lithosphere is known as a plate. The major seven plates are as follows- 1)        African plate 2)        Antarctica plate 3)        Indo-Australian plate 4)        North American plate 5)        South American plate 6)        Pacific plate 7)        Eurasian plate The term tectonic represents the movement of plates. There are three types of plate tectonics or plate movements- 1)         Convergent plate t...
Post a Comment
Read more

What is Diastrophic and Non-diastrophic structure? What is the concept of Diastrophism?

 Before Know about the Diastrophic structure and non-Diastrophic structure we need to comprehend the Diastrophism interaction.  The Concept Of Diastrophism Diastrophism, likewise called tectonism, is the enormous scope misshapen of Earth's outside layer by regular cycles, which prompts the development of landmasses and sea bowls, mountain frameworks, levels, crack valleys, and different provisions by components, for example, lithospheric plate development (that is, plate tectonics), volcanic stacking, or collapsing.     The investigation of diastrophism incorporates the differing reactions of the covering to structural burdens. These reactions incorporate direct or torsional level developments (like mainland float) and vertical subsidence and elevate of the lithosphere (strain) because of normal weights on Earth's surface like the heaviness of mountains, lakes, and icy masses or glaciers.  Diastrophic Structure Any kind of movement of the Earth's crust, gen...
Post a Comment
Read more

What are the importance of Earth's Layers (Crust, Mantle and Core)

  The  seismic waves are the waves of energy that moves through the earth’s layer as a result of forming earthquakes, volcanic eruptions, magma movement, and landslide, etc.  seismic waves are primarily of two types: 1) Body waves:   A body wave is a seismic wave that moves through the interior of the earth. Body waves arrive before the surface wave emitted by an earthquake, these waves are of higher frequency than the surface wave. 2) Surface wave:  The seismic wave that travels through the crust or along the earth's surface, such seismic waves are called surface waves. they  have low frequency and are the most destructive wave. 2)                  The study of seismic waves,  which travel through below the earth’s surface gives a basic idea about the structure of the earth’s interior and the physical properties of its various layers. The seismic waves travel with different velocities in different layers de...
Post a Comment
Read more