$A$ 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:

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

Refractive index of a medium is $\mu$. If the angle of incidence is twice that of the angle of refraction,then the angle of incidence is

$A$ beam of light has a small wavelength spread $\delta \lambda$ about a central wavelength $\lambda$. The beam travels in vacuum until it enters a glass plate at an angle $\theta$ relative to the normal to the plate,as shown in the figure. The index of refraction of the glass is given by $n(\lambda)$. The angular spread $\delta \theta'$ of the refracted beam is given by

An observer can see through a pin-hole the top end of a thin rod of height $h$,placed as shown in the figure. The beaker height is $3h$ and its radius is $h$. When the beaker is filled with a liquid up to a height $2h$,the observer can see the lower end of the rod. Then the refractive index of the liquid is

The optical path of a particular ray of light that has travelled a distance of $3 \ cm$ in flint glass is the same as that of a ray travelling a distance of '$x$' $cm$ through another medium. The value of '$x$' is [refractive index of flint glass $= 1.6$, refractive index of another medium $= 1.25$]. (in $cm$)