The circular part in the centre of the retina is called:

$A$ far-sighted person has a near point of $60\, cm$. What power lens should be used for eyeglasses such that the person can read a book at a distance of $25\, cm$?

For a short-sighted person,the image is formed at

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.

$A$ person cannot see objects clearly placed at a distance of more than $40 \, cm$. He is advised to use a lens of power:

$A$ person who can see things most clearly at a distance of $10 \, cm$ requires spectacles to enable him to see clearly things at a distance of $30 \, cm$. What should be the focal length of the spectacles?