A container is filled with water $\left(\mathrm{\mu }=\frac{4}{3}\right)$ up to height $1 \mathrm{m}.$ Find out diameter of disc at top of water surface from which light is coming out.

As shown in figure light P enters to slab at an angle 60° with normal and inside slab Q makes total internal reflection. Find minimum refractive index
of slab.

A beam of light from a source $L$ is incident normally on a plane mirror fixed at a certain distance $x$ from the source. The beam is reflected back as a spot on a scale placed just above the source $L$. When the mirror is rotated through a small angle $\theta$, the spot of the light is found to move through a distance $y$ on the scale. The angle $\theta$ is given by:

An object is placed at a distance of $40 \mathrm{cm}$ from a concave mirror of focal length $15 \mathrm{cm}$. If the object is displaced through a distance of $20 \mathrm{cm}$ towards the mirror, the displacement of the image will be: