Question

Two thin lenses of focal lengths f1 and f2 placed coaxially in contact. The combination acts as single lens of focal length

Answer 1

The combination of the reciprocal of  focal lengths of two lenses  f1 and f2 is equal  to the sum of reciprocal of focal length of the individual lenses, let the combination of focal length of the resultant lenses be f.

Then 1÷f=(1÷f1)+(1÷f2)

    f=(f1×f2)÷(f1+f2)

The signs of the focal length needed to be taken in to account while calculating the resultant focal length of the lenses.

Answer 2

Answer:

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