When we see an object,the image formed on the retina is

$A$ man cannot see clearly the objects beyond a distance of $20 \, cm$ from his eyes. To see distant objects clearly,he must use which kind of lenses and of what focal length?

$A$ person can see clearly only up to a distance of $25 \, cm$. He wants to read a book placed at a distance of $50 \, cm$. What kind of lens does he require for his spectacles and what must be its power?

When the human eye is focused on an object,the ciliary muscles are least strained when the object is at:

The lens used to correct long-sightedness (hypermetropia) is:

Assertion : In a movie, ordinarily $24$ frames are projected per second from one end to the other of the complete film.
Reason : The image formed on the retina of the eye is sustained up to $1/10 \, s$ after the removal of the stimulus.