$A$ concave mirror of focal length $f$ in air is dipped in a liquid of refractive index $\mu$. Its focal length in the liquid will be $:$

The cross-section of a reflecting surface is represented by the equation $x^{2}+y^{2}=R^{2}$ as shown in the figure. $A$ ray travelling in the positive $x$ direction is directed toward the positive $y$ direction after reflection from the surface at point $M$. The coordinate of the point $M$ on the reflecting surface is

$A$ concave mirror of focal length $f$ produces a real image $n$ times the size of the object. The magnitude of the distance of the object from the mirror is:

An object is placed at a distance of $40 \,cm$ from a concave mirror of focal length $20 \,cm$. The image formed is . . . . . . .

Consider a concave mirror of $10 \,cm$ focal length illuminated by an object kept at a distance of $25 \,cm$. The distance at which the image is formed and its magnification respectively are

Given a point source of light,which of the following can produce a parallel beam of light?