Question

3. If the prism angle is 60°, refractive index
is 2. So what is the minimum deviation
angle ?
A) 30° B) 45° C) 60° D) 90°​

Answer 1

Explanation:

Given: A prism of refractive index

2

has refracting angle 60

∘

.

To find the angle of incidence in order that a ray suffers minimum deviation

Solution:

As per the given criteria,

refractive index of the prism, μ=

2

Angle of the prism, A=60

∘

For minimum angle of deviation we have angle of incidence is equal to angle of emergence, i.e., i=e

Hence, i=

2

A+δ

m

, where δ

m

is the minimum deviation angle.

We know,

μ=

sin

2

A

sin(

2

A+δ

m

)

⟹

2

=

sin

2

60

sini

⟹sini=

2

×sin(30)

⟹sini=

2

×

2

1

Multiply and divide by

2

, we get

sini=

2

1

⟹i=45

∘

In order that a ray suffers minimum deviation it should be incident at an angle 45

∘

is the ans..