When a ray of light is incident normal to the surface separating two different media then refracted ray?

Edited by Sim, Jen Moreau

When a beam of light strikes the boundary separating two transparent media such as air and water or glass, some of the light is reflected whereas the remaining portion enters the second medium and undergoes a change in direction as well as in velocity. This change of direction and velocity of light is called refraction of light.

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Consider a surface A'B' which separates two media. When a ray of light AO passes from one medium to the other, its direction changes along OC instead of straight line AB. Point 'O' is the point of incidence, NO'N is the normal to the surface A'B'. OA is the incident ray and OC is the refracted ray. The angle AON = Li and the angle CON' =Lr. From this discussion and experiment, it is clear that "when a light passes from a rare to a dense medium, the refracted ray bends towards the normal and when a ray of light passes from dense to a rare medium, the refracted ray bends away from normal as shown below (Note: glass is denser than water and water is denser than air).

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Laws of Refraction:

There are two laws of refraction.

Mathematically, n= SinLi/SinLr

Index of Refraction:

When light passes from one medium into another, it is refracted, because the speed of light is different in different media. In general, the speed of light in any medium is less than the speed of light in vacuum. It is, therefore, convenient to define the index of refraction "n" as the ratio of the velocities of light in vacuum or air to the velocity of light in the given medium.

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n= velocity of light in air or vacuum/ velocity of light in medium

n= C/V, where C= 3x108m/s

Note: Since the speed of light in the vacuum is almost equal to the speed of light in air, we use the speed of light in the air instead of vacuum. The refractive index is a ratio of two similar quantities, therefore, having no unit. It only shows the ability of a substance to bend light rays. The refractive index of a substance depends only on the nature of the medium and wavelength and does not depend on the angle of incidence. Moreover, as the apparent depth of water pond seems less than its real depth, we can calculate the refractive index of water as,

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n= Real depth/ apparent depth

Ref: nwater=1.33 and nair= 1.0003

Total Internal Reflection:

When a beam of light passes through an optically denser medium to a rarer medium, i.e. from water to air, the refracted ray bends away from the normal, and the angle of refraction "Lr" is always greater than the corresponding angle of incidence. "Li"

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It should be noted that as the angle of incidence increases, the angle of refraction also increases until a certain value where the corresponding angle of refraction becomes 90º and the refracted ray runs along the surface (separating the two media). When the value of the angle of incidence becomes greater than the critical angle, there is no refraction and the whole ray is internally reflected in the medium, such a process is called total internal reflection.

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Critical Angle:

When the light enters from a denser medium to rarer medium, the value of the angle of incidence for which its corresponding angle of refraction is 90º is called critical angle. Li=Lie, when r= 90º

Conditions for Total Internal Reflection:

The following two conditions are necessary for total internal reflection.

If the critical angle for a specific medium is known, then the refractive index "n" can be found as n= 1/ sin ic

Proof:

The following are applications or examples of total internal reflection.

1. 1

2. 2

3. 3

4. 4

5. 5

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APA (American Psychological Association)
Refraction of Light. (2017). In ScienceAid. Retrieved Oct 19, 2022, from https://scienceaid.net/Refraction_of_Light

MLA (Modern Language Association) "Refraction of Light." ScienceAid, scienceaid.net/Refraction_of_Light Accessed 19 Oct 2022.

Chicago / Turabian ScienceAid.net. "Refraction of Light." Accessed Oct 19, 2022. https://scienceaid.net/Refraction_of_Light.

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