Question

a convex lens of power 2.5 D is placed in contact with a concave lens of power 4.0 D. What is the power of combination? ​

Answer 1

Answer:

25. A convex lens of power + 2.5 D is in contact with a concave lens of focal length 25 cm. The power of combination is. (1) - 1.5 D

Answer 2

Answer:

The power of combination of lenses is $-1.5D$.

Explanation:

Given the power of convex lens,  $P_{1} =2.5 D$

The power of concave lens,$P_{2} =4.0 D$

Power(P) of a lens is the reciprocal of focal length(f) in meters and is measured in diopters.

The power of combination of lenses is equal to the sum of individual powers​, $P=P_{1} +P_{2}$

As the power of concave lens is negative,

Thus, the power of combination of lenses is

$P=2.5-4.0=-1.5D$

Therefore, the power of combination of lenses is $-1.5D$.