Question

A convex lens of focal
length 25 cm and a concave
lens of focal length 10 em are
placed in close contact with
one another, the power of
combination is
21
O 5D
O 6D
O-10 D
O 7D​

Answer 1

Step-by-step explanation:

f1 = 25 cm = 0.25 m

p1 = 1/f1 = 1/0.25 = 4D

f2 = -10 cm = -0.1m

p2 = 1/f2 = 1/-0.1 = -10D

(a) Power of the combination:

P = p1 + p2

= 4D + (-10D)

= - 6 D

(b) Focal length of the combination:

f = 1/P = 1/-6 = -0.1666m = -16.66cm

(c) The combination has negative focal length, so it is diverging.