KEAM 2015 Physics and Chemistry Paper

Key Concept The ratio of sine of the angle of incidence to sine of angle of refraction (I) is a constant called refractive index.
i.e. ‌

sin‌i

sin‌I

=µ (a constant). For two media, Snell's law can be written as,
‌1µ2=‌

µ2

µ1

=‌

sin‌i

sin‌I

Given, refractive index of a prism
n=1.5=‌

3

2

As µ=‌

1

sin‌θ

⇒‌‌µ=‌

1

sin‌60∘

µ=‌

2

√3

⇒sin‌C=‌

1

n

sin‌C=‌

2

3

‌‌⇒‌‌C=sin−1‌

2

3

C=42∘
Angle of incidence > critical angle
So, total internal reflection takes places at second refracting surface.