$A$ 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

$A$ beaker containing liquid is placed on a table,underneath a microscope which can be moved along a vertical scale. The microscope is focused,through the liquid,onto a mark on the table when the reading on the scale is $a$. It is next focused on the upper surface of the liquid and the reading is $b$. More liquid is added and the observations are repeated; the corresponding readings are $c$ and $d$. The refractive index of the liquid is

$A$ ray of light is incident on a medium of refractive index $\mu$ at an angle of incidence $i$. On refraction in the medium,$\delta$ is the angle of deviation. Then:

The frequency of a light ray is $6 \times 10^{14} \,Hz$. Its frequency when it propagates in a medium of refractive index $1.5$, will be

$A$ medium shows the relation between $\sin i$ and $\sin r$ as shown in the graph. If the speed of light in the medium is $nc$,then the value of $n$ is:

$A$ thin oil layer floats on water. $A$ ray of light making an angle of incidence of $40^o$ shines on the oil layer. The angle of refraction of the light ray in water is......$^o$ $({\mu _{oil}} = 1.45, {\mu _{water}} = 1.33)$