Question

A student studies that the speed of light in air is 300000km/s . where that of speed in a glass stab
is about 197000 km/s. What causes the diffeence in speed of light in these two media ?

Answer 1

Given : Speed of light in air is 300000km/s ,where that of speed in a glass slab is about 197000 km/s.

To Find : Causes the difference in speed of light in these two media.

Explanation:

Speed of light in any medium of refractive index η that is  $\[V = \frac{c}{n}\]$

where c is the speed of light. Use the refractive index of air as 1 and that of glass slab as 1.5.

As we know when the medium changes the speed of the light also changes as the refractive index of different mediums is different.

So the speed of the light depends on the refractive index of the medium.

Let c be the speed of light = $\[3 \times {10^8}m/s\]$

And V be the speed of light in the medium.

So  $\[V = \frac{c}{n}\]$ where n = refractive index.

As we know that the value of the refractive index is 1 for air and 1.5 for glass.

So the speed of light in air = $\[{V_{air}} = \frac{{3 \times {{10}^8}}}{1} = 3 \times {10^8}\]$

And the speed of light in glass slab = $\[{V_{glass}} = \frac{{3 \times {{10}^8}}}{{1.5}} = 2 \times {10^8}\]$

So as we see that the speed of light in glass slab is smaller compared to that in air.

Hence, Due to medium changes the speed of the light also changes as the refractive index of different mediums is different is the reason due to difference in speed of light in these two medium.