CUET · PHYSICS · PYQ PAPER 2025
A thin convex lens of refractive index 1.5 has focal length f1. When immersed in a liquid of refractive index 5/3, its focal length is found to be f2. The relationship between f1 and f2 is:
- A \( f_2 = -5f_1 \)
- B \( f_2 = -f_1/5 \)
- C \( f_1 = -5f_2 \)
- D \( f = -3f_2 \)
Answer & Solution
Correct Answer
(A) \( f_2 = -5f_1 \)
Step-by-step Solution
Detailed explanation
\(\frac{1}{f_1} = (\frac{1.5}{1} - 1) (\frac{1}{R_1} - \frac{1}{R_2}) = 0.5 (\frac{1}{R_1} - \frac{1}{R_2})\) \(\frac{1}{f_2} = (\frac{1.5}{5/3} - 1) (\frac{1}{R_1} - \frac{1}{R_2}) = (\frac{9}{10} - 1) (\frac{1}{R_1} - \frac{1}{R_2}) = -0.1 (\frac{1}{R_1} - \frac{1}{R_2})\)…
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