$A$ ray of light incident on a glass sphere (refractive index $\sqrt{3}$) suffers total internal reflection before emerging out exactly parallel to the incident ray. The angle of incidence was (in $^{\circ}$)

$A$ normally incident ray is reflected at an angle of $90^o$. The value of the critical angle is.......$^o$

$A$ water-proof laser pointer of length $10 \,cm$ is placed in a water tank. It rotates about a horizontal axis passing through its centre of mass in a vertical plane as shown in the figure. The time period of rotation is $60 \,s$. Assuming the water to be still and no reflections from the surface of the tank, the duration for which the light beam escapes the tank in one time period is close to ............. $s$. (Take, refractive index of water $= 1.33$)

$A$ ray of light passes from a medium $A$ having refractive index $1.6$ to the medium $B$ having refractive index $1.5$. The value of the critical angle of medium $A$ is . . . . . . .

$A$ monochromatic beam of light is incident at the interface of two materials of refractive index $n_{1}$ and $n_{2}$ as shown. If $n_{1} > n_{2}$ and $\theta_{C}$ is the critical angle,then which of the following statements is $NOT$ true?

$A$ ray of light travelling in a transparent medium falls on a surface separating the medium from air at an angle of incidence of $45^\circ$. The ray undergoes total internal reflection. If $n$ is the refractive index of the medium with respect to air,select the possible value$(s)$ of $n$ from the following: