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

$A$ person's near point is $50 \, cm$ and his far point is $3 \, m$. The power of the lenses he requires for $(i)$ reading and $(ii)$ seeing distant stars are:

$A$ man is suffering from colour blindness for green colour. To remove this defect,he should use goggles of

If the far point of a short-sighted person is $400 \ cm$, then the power of the lens required to enable him to see very distant objects clearly is

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

$A$ 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 ...... $cm$.