Question

The figure shows a surface $X Y$ separating two transparent media, medium-$1$ and medium-$2$. The lines $ab$ and $cd$ represent wave fronts of a light wave traveling in medium-$1$ and incident on $X Y$. The lines $ef$ and $gh$ represent wave fronts of the light wave in medium-$2$ after refraction.

Speed of light is

• A. the same in medium-1 and medium-2
• B. larger in medium-1 than in medium-2
• C. larger in medium-2 than in medium-1
• D. different at b and d

Answer 1

Answer: (B)

Incident and refracted rays are normal to their respective wave fronts, as shown in the figure:

We know that $v_{\text {relative }}=v_{1}-v_{2}$
That is, $\frac{v_{1}}{v_{2}}=\frac{\sin r}{\sin i}$
and $\angle i >\angle r \Rightarrow v_{1} > v_{2}$.
Since $\angle r < \angle i$, medium $2$ is denser than medium $1$ .
Therefore, $v_{2} < v_{1}$