Total flux produced by a source of $1 \ cd$ is

$A$ camera objective has an aperture diameter $d.$ If the aperture is reduced to diameter $d/2,$ the exposure time under identical conditions of light should be made

$A$ water drop in air refracts the light ray as:

Which of the following can form a diminished,virtual,and erect image of your face?

$A$ 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.

$A$ concave mirror is placed on a horizontal table,with its axis directed vertically upwards. Let $O$ be the pole of the mirror and $C$ its centre of curvature. $A$ point object is placed at $C$. It has a real image,also located at $C$ (a condition called auto-collimation). If the mirror is now filled with water,the image will be: