Question

Why does light refracting from water to air not follow Snell's law?

Answer 1

It does follow Snell's Law (

n

1

sin

θ

1

=

n

2

sin

θ

2

) for small angles of incidence

θ

1

.

However, as the angle of incidence becomes bigger, so does the angle of refraction

θ

2

until eventually the angle of refraction is

90

∘

.

At this stage, the angle of incidence is called the critical angle

θ

c

for that interface for light passing from an optically more dense to less dense medium. (

n

1

>

n

2

)

As soon as the angle of incidence exceeds the critical angle, (

θ

1

>

θ

c

) then total internal reflection occurs and obeys the Law of Reflection. (

θ

1

=

θ

2

).