Question

if there is a convex lens of focal length 75cm and cocave lens of focal length 40cm then calculate there combine power​

Answer 1

Answer:

Power of convex lens = 100/f(cm) = 100/75 = +1.33 D.

Power of concave lens = 100/f(cm)

= 100/40 = - 2.5D

Their combined power P = + 1.33 D + (-2.5 D)

P = - 1.17 D.

Their combined focal lenth F’ = 100/P = 100/-1.17

F = - 85.47 cm.

Negative sign indicates that the nature of their combination is concave.