Question

Two lens of power 4d and -5D are kept in contact.Find the focal length of the combination.what is the nature of the combination​

Answer 1

Answer:

Nature of Lens - Concave

Focal Length = -1 m

Explanation:

When two lenses are kept in combination,

1/F = 1/f1 + 1/f2

Here,

1/f1 = 4D

and 1/f2 = -5D

Therefore,

1/F = -1D

F = -1 m

Since, focal length is negative,

The given combination will produce a Concave Lens

Answer 2

f=-1m

Given:

Power of two lenses= 4D and 5D

Combined power= 4D-5D= -1D.

Now,

Power= 1/f(m)

Where ,

f= focal length.

Therefore,

-1= 1/f

f= -1m

Resultant power= -1D

Hence,

The nature of the combination is negative.

This is a concave lens.

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