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

$A$ 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?

$A$ far-sighted man who has lost his spectacles reads a book by looking through a small hole $(3-4 \,mm)$ in a sheet of paper. The reason is:

$A$ person uses a lens of power $+3 \text{ D}$ to normalize vision. The near point of the hypermetropic eye is ....... $m$.

$A$ man suffering from short-sightedness (myopia) is unable to see objects distinctly at a distance greater than $2\,m$. The power of the lens required to correct this defect should be.......$D$

Identify the wrong description of the above figures.