Question

a combination of lens for camera contain two converging lens of focal length 20 cm and 40 cm and a diverging lens of focal length 50 cm find the power and focal length of combination​

Answer 1

Explanation:

From the question we get that the focal

lengths of two convex lenses are given as x = 20 cm and y = 40 cm. And, also the focal length of a concave

lens or the diverging lens is given as

c = -50 cm.

Hence, the equivalent focal length of the combination will be (F):

1/F = 1/a + 1/b + 1/c.

1/F = 1/20 + 1/40 - 1/50.

1/F = 11/200.

S, on solving we will get that.

F = 200/11 = 18.18 cm.

So, the power of the combination will be.

1/F.

1/18.18.

Which on solving.

0.055 D.