Convex lens of power 4D and a concave lens of power 3D are placed in contact. What is the equivalent power of the combination?

Question

Convex lens of power 4D and a concave lens of power 3D are placed in contact. What is the equivalent power of the combination? (A)  (3/4)D  (B)  7D  (C)  (4/3)D  (D)  1D

Tardigrade Admin · Accepted Answer

Here: Power of convex lens = 4D Power of concave lens = 3D Hence, die equivalent power of the combination = 4D - 3D = 1D ( ∵ Concave lens has negative (minus) focal length, so its power will also be negative.)

Q. Convex lens of power 4D and a concave lens of power 3D are placed in contact. What is the equivalent power of the combination?

$\frac{3}{4} D$

$7 D$

$\frac{4}{3} D$

$1 D$

Here: Power of convex lens = 4D Power of concave lens = 3D Hence, die equivalent power of the combination = 4D - 3D = 1D ( $∵$ Concave lens has negative (minus) focal length, so its power will also be negative.)