A myopic person has been using spectacles of power `-1.0` dioptre for distant vision. During old age he also needs to use separate reading glass of power `+0.2` dioptres. Explain what may have happened.

Explanation

Here `u=-25cm, v=-50c, f = ?`
`(1)/(upsilon)-(1)/(u)=(1)/(f) rArr -(1)/(50)+(1)/(25)=(1)/(f)`
`(-1+2)/(50)=(1)/(f) or f=50cm.`
`"As P" =(100)/(f)=(100)/(50)=+2 " dioptres."`