The wavelength of light in air and some other medium are respectively ${\lambda_a}$ and ${\lambda_m}$. The refractive index of the medium is:

An object is immersed in a fluid of refractive index $\mu$. In order that the object becomes invisible when observed from outside,it should

When an object is moved along the principal axis of a concave mirror placed in air,the image coincides with the object if the object is $50 \ cm$ from the mirror. If the mirror is placed at a depth of $20 \ cm$ in a transparent medium,the image coincides with the object when the object is $40 \ cm$ from the mirror. The refractive index of the liquid is

$A$ light ray enters a solid glass sphere of refractive index $\mu=\sqrt{3}$ at an angle of incidence $60^{\circ}$. The ray is both reflected and refracted at the farther surface of the sphere. The angle (in degrees) between the reflected and refracted rays at this surface is......

$A$ light of wavelength $600 \ nm$ in air enters a medium of refractive index $1.5$. Inside the medium :

On a glass plate,a light wave is incident at an angle of $60^o$. If the reflected and the refracted waves are mutually perpendicular,the refractive index of the material is: