Question

A person wears glasses of power `-2.5 D`. Is the person short sighted or long sighted ? What is the far point of the person without glasses ?

Answer 1

Here, `P = -2.5 D`
As `P` is negative, the person is short sighted
`f = (100)/(P) = (100)/(-2.5) = -40 cm`
An object at infinity from the corrective lens must produce the virtual image at the far point, i.e., at `40 cm` from the eye.
From `(1)/(v)=(1)/(f)+(1)/(u)=(1)/(-40)+(1)/(oo)`
`v = -40 cm`.