Question

Two lenses of power 3.5d and -2.5d are placed in contact find power and focal length of the lens construction.

Answer 1

For combination of lenses, the power of each lens is added to get the resultant power.


P = P1 + P2


   = +3.5 – 2.5


   = 1 D


Now, f (in m) = 1/P (in D)


So, f = 1/1 = 1 m = 100 cm