QQuestion
Write down the relationship between relative refractive index and absolute refractive index. On which factors does the relative refractive index of a medium depend? [1 + 2]
OR
Show that if a monochromatic light ray passes symmetrically through an equilateral prism then the angle of deviation of that ray will be minimum
✓Answer
Relative refractive index of medium 2 with respect to medium 1:
1μ2 = μ2 / μ1
where μ2 and μ1 are absolute refractive indices of medium 2 and medium 1.
Factors on which relative refractive index depends:
- Nature of the two media.
- Wavelength (or colour) of the light.
OR
Let the angle of prism A = 60°.
For minimum deviation, the light ray passes symmetrically, i.e. angle
of incidence i = angle of emergence e.
So, angle of refraction r = A/2 = 30°.
Relation:
δmin = 2i – A
Since i = r when symmetrical,
i = A/2 + δmin/2.
Thus, δmin occurs when the ray passes symmetrically through the prism.
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