Question

Two lenses of power -1.75D and +2.75D are placed in contact. What is the focal length of the combination

Answer 1

p=P1+pa_ _ _..........pn

p=P1 + pa = -1.75+2.75=1-25D

p=1/f or f=1/p =( 1/1-25 )m= 0.8m