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

$A$ girl standing at point $P$ on a beach wishes to reach a point $Q$ in the sea as quickly as possible. She can run at $6 \, kmh^{-1}$ on the beach and swim at $4 \, kmh^{-1}$ in the sea. She should take the path

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:

$A$ ray of light travels from air to water to glass and again from glass to air. The refractive index of water with respect to air is '$X$', glass with respect to water is '$Y$', and air with respect to glass is '$Z$'. Which one of the following is correct?

$A$ ray of light is incident at an angle of $75^{\circ}$ into a medium having refractive index $\mu$. The reflected and the refracted rays are found to suffer equal deviations in opposite directions. The value of $\mu$ is:

$A$ ray of light is incident at the glass-water interface at an angle $i$. It emerges finally parallel to the surface of water. Then the value of refractive index of glass,${\mu _g}$,is: