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CUET · PHYSICS · PYQ PAPER 2023

The linear magnifications of the object in the conjugate positions of a convex lens are 4 and 2, respectively. The distance between the conjugate positions is 40 cm . This convex lens of glass \((u=1.5)\) is immersed in water \((u=1.33)\). The new focal length of convex lens in water is :

  1. A 40 cm
  2. B 20 cm
  3. C 60 cm
  4. D 80 cm
Verified Solution

Answer & Solution

Correct Answer

(D) 80 cm

Step-by-step Solution

Detailed explanation

\(2f_{air} = 40 \text{ cm}\) \(f_{air} = 20 \text{ cm}\) \(f_{water} = f_{air} \times \frac{(\mu_{glass} - 1)}{\left(\frac{\mu_{glass}}{\mu_{water}} - 1\right)}\) \(f_{water} = 20 \text{ cm} \times \frac{(1.5 - 1)}{\left(\frac{1.5}{1.33} - 1\right)}\)…