When a ray of light enters from medium A to medium B, its speed decreases and on further entering into medium C, its speed increases.

Which of the following conclusions can be drawn from this ?

Correct Option: Refractive index of A and C are less than B

Step-by-Step Explanation:

1. Understanding Refractive Index and Speed of Light:
The absolute refractive index ($n$) of a medium is inversely proportional to the speed of light ($v$) in that medium. This relationship is given by the formula:

$n=\frac{c}{v}$

where $c$ is the speed of light in a vacuum.
Therefore, a medium in which light travels slower has a higher (optically denser) refractive index, while a medium in which light travels faster has a lower (optically rarer) refractive index.

2. Analyzing the Given Transitions:
- Transition from Medium A to Medium B:
The problem states that when light enters medium B from medium A, its speed decreases ($v_B<v_A$). Since refractive index is inversely proportional to speed, medium B has a higher refractive index than medium A:

$n_B>n_A$

- Transition from Medium B to Medium C:
On further entering medium C from medium B, the speed of light increases ($v_C>v_B$). This implies that medium B has a higher refractive index than medium C:

$n_B>n_C$

3. Combining the Conclusions:
From both observations, we can conclude that the refractive index of medium B is greater than that of medium A and also greater than that of medium C ($n_A<n_B$ and $n_C<n_B$).

Thus, the refractive index of both A and C are less than that of B.