# A convex lens of focal length 40 cm is in contact with a concave lens of focal length 25 cm…

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

(A) – 1.5 D

(B) – 6.5 D

(C) + 6.5 D

(D) + 6.67 D

Ans: (A)

$\large \frac{1}{F} = \frac{1}{f_1} + \frac{1}{f_2}$

$\large \frac{1}{F} = \frac{1}{0.40} + \frac{1}{-0.25}$

$\large P = \frac{1}{F} = -1.5 D$