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NEET 1988 (AIPMT) · Spherical Surfaces & Thin Lenses

Spherical Surfaces & Thin Lenses question from NEET 1988 (AIPMT)

Q112NEET 1988 · AIPMTEasy

Spherical Surfaces & Thin Lenses

Focal length of a convex lens of refractive index 1.5 is 2 cm. Focal length of lens when immersed in a liquid of refractive index of 1.25 will be

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Answer: (c)

  1. Ratio from lens maker's formula: fliqfair=μ−1μμl−1\frac{f_{liq}}{f_{air}} = \frac{\mu - 1}{\frac{\mu}{\mu_l} - 1}
  2. fliq2=0.51.51.25−1=0.50.2=2.5\frac{f_{liq}}{2} = \frac{0.5}{\frac{1.5}{1.25} - 1} = \frac{0.5}{0.2} = 2.5
  3. fliq=5 cmf_{liq} = 5\text{ cm}
  4. So the answer is (c) 5 cm.
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