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:

Find the position of the final image from $O$ for the arrangement shown.

Find linear magnification in the given diagram.

If refractive index of water is $\frac{4}{3}$ then refractive index of unknown medium is:

An astronomical refracting telescope will have large angular magnification and high angular resolution, when it has an objective lens of