Myopia is due to

$A$ 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 $, D$)

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

For a normal eye,the least distance of distinct vision is......$m$.

$A$ 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 wears glasses of power $-2.0 \, D$. The defect of the eye and the far point of the person without the glasses will be