Focal length of a convex lens of refract

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Target Exam

CUET

Subject

Physics

Chapter

Ray Optics

Question:

Focal length of a convex lens of refractive index 1.5 is 2 cm. Focal length of lens when immersed in a liquid of refractive index 1.25 will be

Options:

5 cm

7.5 cm

10 cm

2.5 cm

Correct Answer:

5 cm

Explanation:

$\frac{f_p}{f_a}=\frac{(μ_g-1)}{(\frac{μ_g}{μ_I}-1)}⇒f_I=\frac{5}{2}xf_a$

$\frac{5}{2}×2cm=5cm$