The light when enters the human eye experiences most of the refraction while passing through

$A$ person who can see things most clearly at a distance of $10 \, cm$ requires spectacles to enable him to see clearly things at a distance of $30 \, cm$. What should be the focal length of the spectacles?

The least distance of distinct vision of a long-sighted person is $60 \ cm$. By using a spectacle lens, this distance is reduced to $12 \ cm$. The power of the lens is

When the power of the eye lens increases,a defect of vision is produced. This defect is known as:

Myopia is due to

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