A certain prism is found to produce a minimum deviation of $38°$. It produces a deviation of $44°$ when the angle of incidence is either $42°$ or $62°$. What is the angle of incidence when it is undergoing minimum deviation?

A point object is moving uniformly towards the pole of a concave mirror of focal length $25 \mathrm{cm}$ along its axis as shown below. The speed of the object is $1 {\mathrm{ms}}^{-1}$. At $t=0$, the distance of the object from the mirror is $50 \mathrm{cm}$. The average velocity of the image formed by the mirror between time $t=0$ and $t=0.25 \mathrm{s}$ is:

The following figure shows a beam of light converging at point $P$. When a concave lens of focal length $16 \mathrm{cm}$ is introduced in the path of the beam at a place shown by dotted line such that $OP$ becomes the axis of the lens, the beam converges at a distance $x$ from the lens. The value of $x$ will be equal to