Physical processes are sometimes described visually by lines. Only the following can cross.

Which of the following could not produce a virtual image?

The object distance $u$,the image distance $v$,and the magnification $m$ in a lens follow certain linear relations. These are:

How can we change a camera from $F/4$ to $F/5.6$?

For the refraction of light through a prism,which of the following statements is correct?

$A$ convex mirror of focal length $15 \ cm$ and a concave mirror of focal length $10 \ cm$ are placed facing each other at a distance of $40 \ cm$ apart. $A$ point object is placed between the mirrors on their common axis at a distance of $15 \ cm$ from the concave mirror. The position of the image formed by reflection at the convex mirror will be at a distance of ..... $cm$ from it.