$A$ film projector magnifies a film onto a screen of area $100 \, cm^2$. If the linear magnification is $4$,what will be the area of the image on the screen in $cm^2$?

$A$ thin glass (refractive index $1.5$) lens has an optical power of $-5 D$ in air. Its optical power in a liquid medium with a refractive index of $1.6$ will be:

The formation of a real image using a biconvex lens is shown below:
If the whole setup is immersed in water without disturbing the object and the screen positions,what will one observe on the screen?

$A$ double convex air bubble in water behaves as

An object is placed at the focus of a concave lens having focal length $f$. What is the magnification and distance of the image from the optical centre of the lens?

$A$ point object $O$ is placed on the principal axis of a convex lens of focal length $20 \, cm$ at a distance of $40 \, cm$ to the left of it. The diameter of the lens is $10 \, cm$. If the eye is placed $60 \, cm$ to the right of the lens at a distance $h$ below the principal axis,then the maximum value of $h$ to see the image will be.......$cm$.