Question

Two lenses of power ‐3D and 1.5D are combined and resultant power and focal length of combined lenses . Find the nature ​

Answer 1

When two lenses are kept in contact their powers are added up, so the resultant power of the combined lens

P=P1+PP=3D−1D=2D

As power is positive in sign, so it behaves as a converging or convex lens

Now the focal length of the combined lens is given by

f=

$\frac{1}{p(in \: d =} = \frac{1m}{2} = 50cm$