A ray of light strikes a water-glass interface at an angle of incidence of 35º. The angle of refraction is
A) 40.3º
B) 22.1º
C) 30.6º
D) 59.4º
E) 19.7º

Question

A ray of light strikes a water-glass interface at an angle of incidence of 35º. The angle of refraction is
A) 40.3º 
B) 22.1º 
C) 30.6º 
D) 59.4º 
E) 19.7º

Quizplus · Accepted Answer

According to Snell's law, the ratio of the sine of the angle of incidence (i) to the sine of the angle of refraction (r) is a constant value, which is called the refractive index. Mathematically,

sin(i)/sin(r) = constant

For the water-glass interface, the refractive index of glass is greater than the refractive index of water. Therefore, the light ray bends towards the normal (a line perpendicular to the surface of the interface).

Using Snell's law, we can find the angle of refraction as:

sin(i)/sin(r) = n(glass)/n(water)

sin(r) = sin(i)*n(water)/n(glass) = sin(35º)*1.33/1.5 = 0.306

Thus, the angle of refraction is sin^-1(0.306) = 30.6º (choice C).

A Ray of Light Strikes a Water-Glass Interface at an Angle