A thin flashlight beam traveling in air strikes a glass plate at an angle of 52° with the plane of the surface of the plate.If the index of refraction of the glass is 1.4,what angle will the beam make with the normal in the glass?
A)34°
B)64°
C)26°
D)56°
E)38°

Question

Quizplus · Accepted Answer

Using Snell's law, we can relate the angle of incidence in air (θ₁) to the angle of refraction in the glass (θ₂):

n₁ sin θ₁ = n₂ sin θ₂

where n₁ = 1 (refractive index of air) and n₂ = 1.4 (refractive index of glass).

Rearranging, we get:

sin θ₂ = (n₁/n₂) sin θ₁
sin θ₂ = (1/1.4) sin 52°
θ₂ = sin⁻¹ (0.737) = 47.8°

Now, the angle we want is the angle between the refracted ray and the normal in the glass, which is simply:

θ = 90° - θ₂
θ = 90° - 47.8° = 42.2°

This is closest to choice C) 26°, which is the answer if we had mistakenly used the angle of incidence (52°) instead of the angle of refraction.

A Thin Flashlight Beam Traveling in Air Strikes a Glass