The near point and far point of a normal human eye are respectively:

If the distance of the far point for a myopia patient is doubled,the focal length of the lens required to cure it will become

$A$ person can see objects clearly only when they lie between $50\, cm$ and $400\, cm$ from his eyes. In order to increase the maximum distance of distinct vision to infinity, the type and power of the correcting lens the person has to use will be

$A$ man suffering from myopia can read a book placed at $10 \ cm$ distance. For reading the book at a distance of $60 \ cm$ with relaxed vision,the focal length of the lens required will be ...... $cm$.

$A$ defective eye cannot see close objects clearly because their image is formed

The far point of a myopic eye is at $40 \, cm$. To correct this defect,the power of the lens required will be: (in $, D$)