Ray optics is valid when characteristic dimensions are:

Two light sources with equal luminous intensity are placed at a distance of $1.2\, m$ from each other. Where should a screen be placed between them such that the illuminance on one of its faces is four times that on the other face?

$A$ container is filled with water $(\mu = 1.33)$ up to a height of $33.25\ cm$. $A$ concave mirror is placed $15\ cm$ above the water level and the image of an object placed at the bottom is formed $25\ cm$ below the water level. The focal length of the mirror is (in $cm$)

In the diagram shown,all the velocities are given with respect to the earth. What is the relative velocity of the image in mirror $(1)$ with respect to the image in mirror $(2)$? The mirror $(1)$ forms an angle $\beta$ with the vertical.

Assertion : $A$ concave mirror and convex lens both have the same focal length in air. When they are submerged in water,they will have same focal length.
Reason : The refractive index of water is smaller than the refractive index of air.

For a candle of $40$ power,the exposure time required for a photographic print at a distance of $0.6 \, m$ is $20 \, s$. What will be the exposure time required for the same print at a distance of $1.2 \, m$ using a candle of $20$ power?