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JEE Mains · Physics · STD 12 - 9. Ray optics and optical instruments

A concave-convex lens of refractive index 1.5 and the radii of curvature of its surfaces are 30 cm and 20 cm , respectively. The concave surface is upwards and is filled with a liquid of refractive index 1.3. The focal length of the liquid-glass combination will be _______.

  1. A \(\frac{500}{11} \mathrm{~cm}\)
  2. B \(\frac{800}{11} \mathrm{~cm}\)
  3. C \(\frac{700}{11} \mathrm{~cm}\)
  4. D \(\frac{600}{11} \mathrm{~cm}\)
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Answer & Solution

Correct Answer

(D) \(\frac{600}{11} \mathrm{~cm}\)

Step-by-step Solution

Detailed explanation

\begin{aligned} \frac{1}{\mathrm{f}} & =\left(\frac{1.3-1}{1}\right)\left(\frac{1}{\infty}-\frac{1}{-30}\right) \\ & =\left(\frac{1.5-1}{1}\right)\left(\frac{1}{-30}-\frac{1}{-30}\right) \\ & =\frac{0.3}{30}+\frac{0.5}{60}=\frac{1}{100}+\frac{1}{120} \\ &…

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