Identical rays of light in air are refracted upon entering three transparent materials:
A) water, (where the speed of light is 0.75c);
B) ethyl alcohol (speed 0.7c); and
C) crown glass (speed 0.6c).
Rank the materials according to how much the light ray bends toward the normal, from most bending to least bending.

Explanation:

for us to rank them we need to calculate the angle of refraction for the various materials. The angle of refraction is the angle between the refracted ray and the normal.

refractive index(n) = velocity of light in air/ velocity of light in medium

refractive index (n) = sini/sinr

lets equate the right side of both equations.

we will assume 30 degree as the angle of incidence for all materials.

(a) water

sinr = 0.75c/c *sin30

sinr = 0.375

r= arcsin0.375

r=22.02°

(b) ethyl alcohol

sinr = 0.7c/c *sin30

sinr = 0.35

r= arcsin0.35

r=20.49°

(c) crown glass

sinr = 0.6c/c *sin30

sinr = 0.3

r= arcsin0.35

r=17.46°

it is observed that the angle of refraction decreases as the velocity of light in glass decreases.

ranking the materials  according to how much the light ray bends toward the normal, from most bending to least bending we have;

Crown glass > ethyl alcohol> water

speed of light in vacuum is 300,000 km/s

speed of light in other mediums is given by the expression v = c/n, where c is the speed of light in vacuum and n is the refractive index of medium.

for the first medium v = 200,000 km/s

  so, refractive index of medium = 300000/200000 = 1.5

    1.5 refractive index is usually for glass. so first medium is glass.

for the second medium v = 250,00 km/s

so, refractive index of medium = 300000/250000 = 1.2

    1.2 refractive index is usually for water. so second medium is water.

for the third medium v = 0 km/s

so, refractive index of medium = 300000/0 = ∞

    ∞ refractive index is usually for opaque mediums. so third medium is opaque medium.