Focal length of a convex lens of refract

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Home Questions PG94C2C365

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:

$\frac{f_p}{f_a}=\frac{\left(\mu_g-1\right)}{\left(\frac{\mu_g}{\mu_l}-1\right)} \Rightarrow f_l=\frac{5}{2} \times f_a$

$\frac{5}{2} \times 2$ cm = 5 cm