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Physics-Refraction

NEET Physics Refraction MCQ Question

Type: MCQ-numerical-Hard-Class 12

A double convex lens forms an image using two refracting surfaces. If the refractive index of the lens material is 1.5 and the radius of curvature of both surfaces is 20 cm, what is the focal length of the lens?

A

13.3 cm

B

15.0 cm

C

20.0 cm

D

26.7 cm

Correct Answer

Option A

Detailed Explanation

Using the lens maker's formula for a thin lens, 1f=(n−1)(1R1−1R2)\frac{1}{f} = (n - 1) \left( \frac{1}{R_1} - \frac{1}{R_2} \right), substituting n=1.5n = 1.5, R1=20 cmR_1 = 20 \text{ cm}, and R2=−20 cmR_2 = -20 \text{ cm}, the focal length f=13.3 cmf = 13.3 \text{ cm}.

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