$A$ man can see clearly up to $3 \, m$. Prescribe a lens for his spectacles so that he can see clearly up to $12 \, m$.

$A$ person suffering from hypermetropia cannot focus on objects closer than $120 \, cm$. To read at a distance of $40 \, cm$,what should be the focal length of the lens required?

Calculate the focal length of a reading glass of a person if his distance of distinct vision is $ 75 \ cm $. (in $cm$)

$A$ 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.......$D$

Your friend is having an eyesight problem. She is not able to see a distant uniform window mesh clearly,and it appears to her as non-uniform and distorted. The doctor diagnosed the problem as:

An imaginary line joining the optical centre of the eye lens and the yellow point is called as