Light propagates faster through a medium “a” than medium “b”

1. which of these medium has a higher optical density ?
2. state the condition under which no change in direction of propagation of a light ray would take place when it passes through medium “a” to medium “b”

1) The medium b has higher optical density.

2) If the optical densities of both A and B are same.

Explanation:

The refractive index of a material determines the number of times the velocity of light in that material is slower than the velocity of light in a vacuum. The higher refractive index means slower propagation of the light in that medium. The refractive index of the medium determines the optical density of the medium. If the material has a higher refractive index, then its optical density is high. If the material has a low refractive index, then its optical density is low. The light bends towards the normal while refracting through the medium from a lower optical density medium to the higher optical density medium. If both the mediums has the same optical density, the direction of propagation doesn't change.