Total Internal Reflection Formula and Example Problems

Total Internal Reflection Formula :

Total internal Reflection formula is the refractive index in medium  n1  and divided by the refractive index in medium 2 n2 is equal to the  angle of refraction sin r and divided by the angle of incidence sin i. Hence the Total internal Reflection formula can be written as

Total internal reflection n1/n2 =sin r / sin i

Critical angle θ =Sinθ =n2 /n1

R → angle of refraction

I→ angle of incidence

n1 → refractive index in medium 1

n2→ refractive index in medium 2

θ→ critical angle



An optical fiber made up the glass with refractive index n1=2.5 which is surrounded by another glass of refractive index n2 of the cladding such that the critical angle between the two cladding is  900


Ciritical angle θ =900

Refractive index n1=2.5

Refractive index n2=?

Using the below formula we can calculate n2

Sin θ =n2 /n1

Sin 900 =n2/ 2.5

N2=2.5* sin 900



Calculate the refractive index of the medium whose critical angle 300 ?


Critical angle θ=300

Refractive index of the medium μ=?

μ =1/ sin θ

μ =1/ sin 400



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