A person cannot see the objects distinctly, when placed at a distance less than `100 cm`. What is the power of the spectacles that he should use to see clearly, the objects placed at `25 cm` ?

Answer

`+ 3D`

Explanation

Here, `u = -25 cm, v = -100 cm, f = ?`
`(1)/(f)=(1)/(v)-(1)/(u)=(1)/(-100)+(1)/(25)=(-1 + 4)/(100)=(+3)/(100)`
`f = (100)/(3) cm = (1)/(3) m`
`P = (1)/(f) = (1)/(1//3) = 3 D`.