Convex lens of 10 cm focal length is com

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Target Exam

CUET

Subject

Physics

Chapter

Ray Optics

Question:

Convex lens of 10 cm focal length is combined with a concave lens of 6 cm focal length. Find the focal length of the combination.

Options:

15 cm

– 15 cm

30 cm

– 30 cm

Correct Answer:

– 15 cm

Explanation:

Here f₁ = 10 cm, f₂ = -6 cm, F = ?

Use the formula $\frac{1}{F}=\frac{1}{f_1}+\frac{1}{f_2}=\frac{1}{10}-\frac{1}{6}=-\frac{1}{15}$

∴ F = −15 cm