The impact of an image on the retina remains for......$sec$.

If the least distance of distinct vision for a boy is $35 \ cm$,then the lens to be used by the boy for correcting the defect of his eye is

An imaginary line joining the optical centre of the eye lens and the yellow point is called as

The diameter of the eye-ball of a normal eye is about $2.5\, cm$. The power of the eye lens varies from

$A$ presbyopic patient has a near point of $30 \ cm$ and a far point of $40 \ cm$. The dioptric power of the corrective lens required for seeing distant objects is: (in $D$)

$A$ man can see objects clearly between $15 \ cm$ and $30 \ cm$. He uses a lens to see far objects. Due to the lens used,the new near point will be at........$cm$.