A boy uses spectacles of focal length -60cm. Name the defect of vision he is suffering from. Which lens is used for the correction of this defect? Compute the power this lens.

Focal length = f

f = -60 cm (Given)

= -0.60m

The negative sign of focal length indicates that the lens used is concave hence the boy is suffering from myopia (short sightedness).

Power of the lens =

=

= -1.667 D