The speed of light in a medium is $200 \times 10^8 \text{ cm/s}$. The refractive index of the medium is . . . . . . $(c = 3 \times 10^8 \text{ m/s})$.

An electromagnetic wave of wavelength $\lambda_0$ (in vacuum) passes from $P$ towards $Q$ crossing three different media of refractive index $\mu, 2\mu$ and $3\mu$ respectively as shown in the figure. Let $\phi_P$ and $\phi_Q$ be the phase of the wave at points $P$ and $Q$. Find the phase difference $\phi_Q - \phi_P$. [Take: $\mu = 1$]

An observer can see through a small hole on the side of a jar (radius $15\, cm$) at a point at a height of $15\, cm$ from the bottom (see figure). The hole is at a height of $45\, cm$. When the jar is filled with a liquid up to a height of $30\, cm$,the same observer can see the edge at the bottom of the jar. If the refractive index of the liquid is $N/100$,where $N$ is an integer,the value of $N$ is $.....$

$A$ ray of light passes through four transparent media with refractive indices $\mu_1, \mu_2, \mu_3$ and $\mu_4$ as shown in the figure. The surfaces of all media are parallel. If the emergent ray $CD$ is parallel to the incident ray $AB$,we must have

White light consists of wavelengths ranging from $480 \,nm$ to $672 \,nm$. What will be the wavelength range when white light is passed through glass of refractive index $1.6$?

The refractive index of a medium is $\frac{3}{2}$. The speed of light in this medium is . . . . . . $ms^{-1}$. (Speed of light in vacuum is $c = 3 \times 10^{8} \,ms^{-1}$)