A student studies that speed of light in air is 300000 kms/ sec where that of speed in a
glass slab is about 197000 kms/ sec. What causes the difference in speed of light in these
two media?
a) difference in density
b) difference in temperature
c) difference in amount of light
d) difference in direction of wind flow.
Answers
Answer:
The following question is important.
Explanation:
(a) Difference in density
Density here refers to optical density of a medium.
Option (a) difference in density causes the difference in speed of light in the two media.
Given: A student studies that speed of light in air is 300000 kms/ sec where that of speed in a glass slab is about 197000 kms/ sec.
To find: Cause of difference of speed of light in the two media
Solution: Speed of light in air =300000 km/s
Speed of light in glass slab= 197000 km/s
Optical density of the material is the measure of the speed of light through the material with respect to vacuum.
The material can be optically denser(light speed decreases when material is optically dense) or optically rarer(light speed increases when material is optically rare) with respect to any given material.
It is different from the mass density of the material.
Optical density of vacuum is 1 ,air is 1.003 while the optical density of glass is 1.52 .
Since the optical density of air is just greater than vacuum, the light does not undergo any speed difference.
But the optical density of glass is significantly greater than vacuum, which is the reason why speed decreases to a large extent in glass slab.