1. Tardigrade
  2. Question
  3. Physics
  4. The plane faces of two identical plano-convex lenses, each having focal length of 40 cm, are placed against each other to form a common convex lens. The distance from this lens at which an object must be placed to obtain a real inverted image with magnification equal to unity is

Question Error Report

Thank you for reporting, we will resolve it shortly

Back to Question

Q. The plane faces of two identical plano-convex lenses, each having focal length of 40 cm, are placed against each other to form a common convex lens. The distance from this lens at which an object must be placed to obtain a real inverted image with magnification equal to unity is

Rajasthan PMTRajasthan PMT 2009

Solution:

Focal length of the combination lens, $ \frac{1}{f}=\frac{1}{{{f}_{1}}}+\frac{1}{{{f}_{2}}}=\frac{1}{40}+\frac{1}{40} $ $ \therefore $ $ f=20\,\,cm $ Given, $ m=1 $ $ m=\frac{f}{u-f} $ $ 1=\frac{20}{u-20} $ $ u-20=20 $ $ u=40\,\,cm $