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Question
You are given the following three lenses. Which two lenses will you use as an eyepiece and as an objective to construct a compound microscope?
| Lenses | Power (D) | Aperture (cm) |
| L1 | 3 | 8 |
| L2 | 6 | 1 |
| L3 | 10 | 1 |
Solution
For a compound microscope, an objective is so chosen that its aperture is small and focal length is very small whereas an eyepiece is so chosen that its aperture is large and focal length is moderate. Now,
focal length of L1, f1 = 1/3 = 0.33 m
focal length of L2, f2 = 1/6 = 0.166 m
focal length of L3, f3 = 1/10 = 0.1 m
Therefore, from the above calculation of focal length and given aperture, it shows that L1 will be suitable for eyepiece and L3 for objective.
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