Question

When a ray of light travels a distance d in a medium of refractive index n, then the
optical path in the medium is
(A) n+d
(B) n-d
(C) nd
Đ) n/d​

Answer 1

Explanation:

Two light rays having the same wavelength λ in vacuum are in phase initially. Then the first ray travels a path L1 through a medium of refractive index n1 while the second ray travels a path of length L2 through a medium of refractive index n2. The two waves are then combined to produce interference. The phase difference between the two waves is:

Answer 2

(C)  nd .

• Refractive index, also called index of the  refraction, measure of bending of a ray of light when  the  passing from one medium into  the  another.

• When a ray of light travels from the  optically denser medium to the  optically rarer medium, it always bends away from normal.

• According to Snell's Law:  

                  n2 / n 1 = sinr/sini

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• For optically denser the  medium, refractive index n 1 is greater than  the of rarer medium n 2 .

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• Thus, the angle of refraction has to be greater than the  angle of incidence i.e. it bends away from the normal.

• medium 1 is optically denser because when light travels from denser to rarer medium light bends away from normal.

Hence the answer is Option (C)  nd .

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