Question 1

Why does a ray bend toward the normal when it enters glass from air?

Accepted Answer

Glass has a higher refractive index than air, so the light travels more slowly in glass and its direction changes at the boundary. The refracted angle r is smaller than the incident angle i when both are measured from the normal.

Question 2

What happens to a ray after passing through a parallel-sided glass slab?

Accepted Answer

The emergent ray is parallel to the incident ray because the two faces of the slab are parallel. The ray is not on exactly the same line, however: it has a lateral displacement, which is why it appears shifted from its original path.

Question 3

What is the angle between the two refracting surfaces of a prism called?

Accepted Answer

It is called the prism angle or refracting angle A. For the internal path through the prism, the geometry gives A = r1 + r2, where r1 and r2 are the refractions at the two surfaces.

Question 4

What is minimum deviation in a prism?

Accepted Answer

Minimum deviation is the symmetric orientation of a prism in which the angle of incidence equals the angle of emergence, i = e. The two internal refraction angles are also equal, so r1 = r2 = A/2 and delta_min = 2i - A.

Question 5

How is the refractive index of a prism calculated at minimum deviation?

Accepted Answer

For a prism in air, the refractive index at minimum deviation is n = sin[(A + delta_min) / 2] / sin(A/2). Here A is the prism angle and delta_min is the smallest total deviation for that prism.

Refraction & Prism Lab — Bending, Shifting and Prism Deviation in 3D

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