A convex lens of focal length f₁ is kept in contact with a concave lens of focal length f₂. Find the focal length of the combination.

Solution

Focal length of convex lens = +f₁

Now, using lens formula, we have
$plus 1 over straight f subscript 1 space equals space fraction numerator 1 over denominator v apostrophe end fraction space minus space 1 over u$ ... (1)

For concave lens of formula, focal length is (-f₂)
$negative 1 over straight f subscript 2 equals 1 over v space minus space fraction numerator 1 over denominator v apostrophe end fraction space$ ... (2)
Now, adding equations (1) and (2), we have
$1 over straight f subscript 1 space minus space 1 over f subscript 2 space equals space 1 over v space minus space 1 over u$ ... (3)

Now, for the combined lens using the lens formula, we have,
$1 over straight f space equals space 1 over v space minus space 1 over u$ ... (4)
Therefore, from equations (3) and (4), we have
$1 over straight f space equals space 1 over f subscript 1 space minus space 1 over f subscript 2$

This is the required focal length of the combination of lenses.

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A convex lens of focal length f₁ is kept in contact with a concave lens of focal length f₂. Find the focal length of the combination.

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Wave Optics

A convex lens of focal length f1 is kept in contact with a concave lens of focal length f2. Find the focal length of the combination.

Some More Questions From Wave Optics Chapter

Mock Test Series

NCERT Sample Papers

Entrance Exams Preparation

A convex lens of focal length f₁ is kept in contact with a concave lens of focal length f₂. Find the focal length of the combination.