$A$ ray is incident from a medium of refractive index $2$ into a medium of refractive index $1$. The critical angle is (in $^{\circ}$)

$A$ light ray from air is incident (as shown in figure) at one end of a glass fiber (refractive index $\mu = 1.5$) making an incidence angle of $60^o$ on the lateral surface,so that it undergoes a total internal reflection. How much time would it take to traverse the straight fiber of length $1 \ km$ (in $\mu s$)?

$A$ light ray falls on a square glass slab as shown in the diagram. The index of refraction of the glass,if total internal reflection is to occur at the vertical face,is equal to

Explain the experiment which demonstrates total internal reflection.

Assertion: The maximum refractive index of the liquid for total internal reflection of the ray passing through the prism as shown in the figure must be $\sqrt 2$.
Reason: Here,the critical angle is $45^o$.

Glass has refractive index $\mu$ with respect to air and the critical angle for a ray of light going from glass to air is $\theta$. If a ray of light is incident from air on the glass with angle of incidence $\theta$,the corresponding angle of refraction is: