Laws of Refraction


 
 
Concept Explanation
 

Laws of Refraction

The way a ray of light refracts when it is incident on the surface separating two media depends not only on the refractive indices of the media but also on the angle of incidence.

In the given figure there are two mediums : Air and Water. Let their refractive indices be n _1 and n _2 respectively. The two media can be any pair such as air and water, or air and glass. Suppose a ray of light called as incident ray traveling in medium air,  is incident on the surface of water body . Draw a normal  to the surface at the point of incidence of incident ray.

The angle i formed between the incident ray and the normal is called the angle of incidence(angle i).

The angle r between the refracted ray and the normal is called the angle of refraction(angle r).

The ray of light inside the medium is called as refracted ray.

Laws Of Refraction:

Two laws of refraction governs the refraction that takes place at a surface of separation.

1.  The incident ray, the normal and the refracted ray to the refracting surface at the point of incidence lie in the same plane.

2.  The angle of incidence and the angle of refraction satisfy the equation

frac{sin; i}{sin; r}= frac{n _2}{n_1}

The second law given above is also called Snells law.

Illustration: A ray of light traveling in air falls on the surface of a material. The ray makes an angle of 450 with the normal to the surface. Find the angle made by the refracted ray with the normal in the material. Refractive index of the material is sqrt 2.

Solution: Since the ray makes angle of 450 with the normal, So angle of incidence is

angle i= 45 ^0

The ray is traveling in air and  the refractive index of air is 1

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Sample Questions
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Question : 1

In the speed of light is slower in medium B then in medium A ,Then which of the following statement is true ?

Right Option : B
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Question : 2

The angle of refraction is the angle that the __________makes with me _____

Right Option : D
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Question : 3

Which of the following are correct ?

(a) The way a ray of light refracts when it is incident on the surface separating two media depends not only on the refractive indices of the two media but also on the angle of incidence.

(b) The angle formed between the incident ray and the normal is called the angle of refraction.

(c) The ray of light coming from medium 1 when it is inside the medium it 2 is called as refracted ray .

Right Option : C
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