A light ray traveling from a higher index of refraction medium into a lower index of refraction medium (for example, from water into air) would bend away from the normal to the medium surface. When the refracted ray is parallel to the boundary of the medium, θ2 = 90°. The incident angle, θ1, becomes θc, called the a. Cauchy angle b. classic angle c. critical angle d. conjugate angle

option C

Explanation:

The correct answer is option C

When the ray of light pass from higher refractive index to lower refractive index then the light bend away from the normal.

when the refracted ray is parallel to the boundary of the medium, θ₂ = 90°

and the incident angle θ₁

so, the angle θc is known as the critical angle.

At critical angle the refracted ray becomes parallel to boundary surface.