$A$ fish rising vertically up towards the surface of water with speed $3 \; ms^{-1}$ observes a bird diving vertically down towards it with speed $9 \; ms^{-1}$. The actual velocity of the bird is.......$ms^{-1}$ (Assume refractive index of water $\mu = 4/3$).

$A$ magician during a show makes a glass lens with $n = 1.47$ disappear in a trough of liquid. What is the refractive index of the liquid? Could the liquid be water?

Electromagnetic radiation of frequency $n$,wavelength $\lambda$,travelling with velocity $v$ in air,enters a glass slab of refractive index $\mu$. The frequency,wavelength,and velocity of light in the glass slab will be respectively:

The angles of incidence and refraction of a monochromatic ray of light of wavelength $\lambda$ at an air-glass interface are $i$ and $r$,respectively. $A$ parallel beam of light with a small spread $\delta \lambda$ in wavelength about a mean wavelength $\lambda$ is refracted at the same air-glass interface. The refractive index $\mu$ of glass depends on the wavelength $\lambda$ as $\mu(\lambda)=a+b / \lambda^2$,where $a$ and $b$ are constants. Then,the angular spread in the angle of refraction of the beam is

When light enters from air to water,then its

The speed of light is maximum in