Question

A person wears glasses of power − 2.5 D. Is the person farsighted or nearsighted? What is the far point of person without the glasses?

Answer 1

The person must be near-sighted because the person wears glasses of power –2.5 D.
For a near-sighted person, u = ∞.
Focal length, f = `1/( text/"Power") = 1/ ((-2.5)) = -0.4text/" m" = -40 text/" cm"` The lens formula is given by

`1/v -1/u =1/f`

Putting the values , we get:

`1/v = 1/∞ + 1/((-40))`

⇒ v = -40 

So, the far point of the near-sighted person is 40 cm.