A ray of light is incident normally on one face of prism of angle 30 and R.I.=root2. What will be the angle of deviation?

Refractive index = root 2 (given)

sin angle incidence/sine angle refraction = root 2

sin angle 90/sine angle r = root 2 (as ray is incident normally)

sine angle r = 1/root 2

sine angle 45 = 1/root 2

Angle r = 45 degree............1

Now, the sum of two interior opposite angles of a triangle is equal to its exterior angle.

In the case of prism,

Angle of deviation = angle of refraction,r₁ + angle of refraction.r₂

= 2 angle of refraction (As r₁=r₂)

= 2*45 (from 1)

= 90 degree.

that's not the answer