Question

Focal length of the combination of convex lens of focal length 30 cm and the concave lens of focal length 20cm in contact in the system of converging or diverging lens

Answer 1

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Answer 2

Given that,

Focal length of the convex lens, f = 30 cm

Focal length of the concave lens, f' = -20 cm

To find,

The focal length of the combination.

Solution,

The focal length of the combination is given by :

$\dfrac{1}{f}=\dfrac{1}{f}+\dfrac{1}{f'}\\\\\dfrac{1}{f}=\dfrac{1}{(30)}+\dfrac{1}{(-20)}\\\\f=-60\ cm$

So, the focal length of the combination is (-60 cm).

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Combination of lens

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