JEE Mains · Physics · STD 12 - 9. Ray optics and optical instruments
A plano-convex lens having radius of curvature of first surface 2 cm exhibits focal length of \(f_1\) in air. Another plano-convex lens with first surface radius of curvature 3 cm has focal length of \(\mathrm{f}_2\) when it is immersed in a liquid of refractive index 1.2 . If both the lenses are made of same glass of refractive index 1.5 , the ratio of \(f_1\) and \(f_2\) will be _______.
- A \(1: 2\)
- B \(1: 3\)
- C \(3: 5\)
- D \(2: 3\)
Answer & Solution
Correct Answer
(B) \(1: 3\)
Step-by-step Solution
Detailed explanation
For case (1) \(\begin{aligned} & \frac{1.5}{v_1}-\frac{1}{\propto}=\frac{(1.5-1)}{R_1} \\ & \frac{1}{f_1}-\frac{1.5}{v_1}=\frac{1-1.5}{\propto}\end{aligned}\) \(\Rightarrow \frac{1}{f_1}=\frac{(1.5-1)}{R_1}\) ...(1) \(\Rightarrow \frac{1}{f_1}=\frac{1}{2 R_1}\) For case (2)…
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