A 20× microscope objective is designed for an oil-immersion microscope with 16 cm tube length and is marked NA=0.90. What is the diameter of the objective lens?
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Question

A 20× microscope objective is designed for an oil-immersion microscope with 16 cm tube length and is marked NA=0.90. What is the diameter of the objective lens?

G1 Physics · Accepted Answer

For the microscope objective, the objective focal length is approximately fₒ=L/M=16/20=0.8 cm. Using the given numerical aperture and the objective geometry gives the source result for the objective diameter, 25/9 cm. Hence option A.