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CUET · PHYSICS · PYQ PAPER 2023

The focal length of a thin lens in vacuum is f. If the material of the lens has refractive index \( \frac{3}{2} \), its focal length when immersed in water of refractive index \( \frac{4}{3} \) would be :

  1. A 2f
  2. B f
  3. C 4f
  4. D \( \frac{4f}{3} \)
Verified Solution

Answer & Solution

Correct Answer

(C) 4f

Step-by-step Solution

Detailed explanation

\( \frac{1}{f} = (n_l - 1) \left( \frac{1}{R_1} - \frac{1}{R_2} \right) \) \( \frac{1}{f_w} = \left( \frac{n_l}{n_w} - 1 \right) \left( \frac{1}{R_1} - \frac{1}{R_2} \right) \) \( f_w = f \frac{n_l - 1}{\frac{n_l}{n_w} - 1} \)…