Question

A convex lens of focal length 40cm is in contact with a concave lens of focal length 25cm. The power of the combination is

• A. -1.5 D
• B. -6.5 D
• C. +6.5 D
• D. + 1.5 D

Answer 1

The correct option is A -1.5 D

$\text{The power of combination of lenses}\text{is given as}P=P1+P2=\frac{1}{f_1}+\frac{1}{f_2}=\left(\frac{1}{0.4}\right)-\frac{1}{0.25}=-1.5D$