Question

A girl uses spectacles of focal length-60 Name the defect of vision she is suffering from which lens is used for the collection of these defect Compute the power of lens

Answer 1

Since the focal length is a +ve value, the defect should be LONG SIGHTNESS(Heteromyopia) coz convex lens has +ve value for focal length as the image will be formed behind the lens.

Power= 1/focallength(m)

--->         1/60

--->      P= +0.016 D

Answer 2

Given:- Focal length = -60cm

Since focal length is negative the lens used is Concave lens

We know, 1m= 100cm

therefore, -60cm= -0.6m

Power = 1/focal length , where focal length is in meters

P= 1/-0.6

P= -10/6

P= -1.67D

The defect of vision she is suffering is Myopia [Short Sightedness]