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CUET · PHYSICS · PYQ PAPER 2025

If the radii of curvature of the faces of a double convex lens are 10 cm and 15 cm, respectively and its refractive index is 1.5, the focal length of the lens in air is

  1. A 6 cm
  2. B 12 cm
  3. C 30 cm
  4. D 28 cm
Verified Solution

Answer & Solution

Correct Answer

(B) 12 cm

Step-by-step Solution

Detailed explanation

\( \frac{1}{f} = (n - 1) \left( \frac{1}{R_1} - \frac{1}{R_2} \right) \) \( \frac{1}{f} = (1.5 - 1) \left( \frac{1}{10} - \frac{1}{-15} \right) \) \( \frac{1}{f} = (0.5) \left( \frac{1}{10} + \frac{1}{15} \right) \) \( \frac{1}{f} = 0.5 \left( \frac{3+2}{30} \right) \)…