MHT-CET : Physics Entrance Exam

### MHT - CET : Physics - Wave Theory of Light Formulae Page 1

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1. Refractive Index

na = R.I. of medium 'a' w.r. to air or vacuum =

 c va

where c = velocity of light in the air or vacuum and va = velocity of light in medium 'a'

2. Snell's Law

Refractive index n =

 sin i sin r

(Snell's law).

 where i = angle of incidence r = angle of refraction

3. Frequency of a Light Wave

frequency v =

 c l

 where c = velocity of wave ( in air) l = wavelength

As the ray of light travels from a rarer medium to a denser medium, its velocity decreases but frequency remains the same.
Frequency of the wave does not depend upon the medium, it depends upon the source.

4. Relation Between ang and gna

ang = R.I. of glass w.r. to air
gna = R.I. of air w.r. to glass

ang =

 1 gna

5. Relation Between Refractive Index, Velocity and Wavelength of a Wave

anb =

 nb na

nb = R. I. medium 'b' w.r. to air or vacuum

na = R. I. medium 'a' w.r. to air or vacuum

=

 va vb

va = velocity of light in medium 'a'

vb= velocity of light in medium 'b'

=

 la lb

la = wave length of light in medium 'a'

lb = wave length of light in medium 'b'

6. Width of Wave Front

Cos i = Width of incident wave front
Cos r = Width of refracted wave front

 where i = angle of incidence r = angle of refraction

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