Question

49. A concave lens having f = 20 cm is in contact with a convex lens having f = 0.45 m. What is the combined power D? ​

Answer 1

The combined power D is -0.36D

Given :

A concave lens having f = 20 cm

A convex lens having f = 0.45m=45cm

To find :

The combined power D

Solution :

The net focal length of the combination is

$1/f=1/f_1+1/f_2\\\\1/f=1/45+1/-20\\\\1/f=1/45-1/20\\1/f =20-45/900\\\\1/f=-25/900\\\\\1/f=-1/36$

Power = 1/f

Power = -0.36D

Thus, the combined power D is -0.36D

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Answer 2

Answer: The combined power of the two lenses is -2.78 D.

The power (P) of a lens is defined as the reciprocal of its focal length (f) in meters, i.e., P = 1/f.

The power of a concave lens is negative, and the power of a convex lens is positive.

In this problem, we have a concave lens with f = 20 cm = 0.2 m and a convex lens with f = 0.45 m.

The power of the concave lens is

 P1 = -1/0.2 m = -5 D (D is the unit of power, which stands for diopters).

The power of the convex lens is

                         P2 = 1/0.45 m = 2.22 D.

To find the combined power of the two lenses, we need to add their powers:

                        P = P1 + P2 = -5 D + 2.22 D = -2.78 D

Therefore, the combined power of the two lenses is -2.78 D.

Learn more about convex lenses here

https://brainly.in/question/1333877

Learn more about concave lenses here

https://brainly.in/question/1301518

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