We wish to make a microscope with the help of two positive lenses both with a focal length of 20 mm each and the object is positioned 25 mm from the objective lens. How far apart the lenses should be

Question

We wish to make a microscope with the help of two positive lenses both with a focal length of 20 mm each and the object is positioned 25 mm from the objective lens. How far apart the lenses should be so that the final image is formed at infinity?

TestHub · Accepted Answer

To obtain final image at infinity, object which is the image formed by objective should be at focal distance of eye-piece. By lens formula (for objective) $or, \Rightarrow ∴ \frac{1}{v _{0}} - \frac{1}{u _{0}} = \frac{1}{f _{0}} \frac{1}{v _{0}} - \frac{1}{- 25} = \frac{1}{20} \frac{1}{v _{0}} = \frac{1}{20} - \frac{1}{25} = \frac{5 - 4}{100} = \frac{1}{100} mm v_{0} = 100 mm$ Therefore the distance between the lenses $= v_{0} + f_{e} = 100 mm + 20 mm = 120 mm$

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