$A$ monochromatic beam of light is travelling from medium $A$ of refractive index $n_{1}$ to a medium $B$ of refractive index $n_{2}$. In the medium $A$,there are $x$ number of waves in a certain distance. In the medium $B$,there are $y$ number of waves in the same distance. Then,the refractive index of medium $A$ with respect to medium $B$ is

The phase difference between the incident wave and the reflected wave is $180^o$ when a light ray:

When light is refracted from air into glass,

If $n_{21} > 1$,then write the relation between the angle of incidence and the angle of refraction.

If light passes near a massive object,the gravitational interaction causes a bending of the ray. This can be thought of as happening due to a change in the effective refractive index of the medium given by $n = 1 + \frac{2GM}{rc^2}$,where $r$ is the distance of the point of consideration from the centre of the mass of the massive body,$G$ is the universal gravitational constant,$M$ is the mass of the body,and $c$ is the speed of light in vacuum. Considering a spherical object,find the deviation of the ray from the original path as it grazes the object.

$A$ light ray is incident on a transparent sphere of refractive index $\mu = \sqrt{2}$ at an angle of incidence $i = 45^{\circ}$. What is the total deviation of a ray that enters the sphere,undergoes two internal reflections,and then refracts out into the air (in $^{\circ}$)?