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NEET2026PhysicsChapterActual

A researcher is adjusting a compound microscope to view a bacterial sample. The microscope has an objective lens of focal length 1.5 cm and an eyepiece of focal length 5.0 cm . If the researcher wants to achieve a total magnifying power of 200 for a relaxed eye (normal adjustment), what must be the tube length of the microscope? (Take the least distance of distinct vision as 25 cm )

Options

  1. A40 cm
  2. B50 cm
  3. C60 cm
  4. D75 cm

Correct answer

C. 60 cm

Step-by-step solution

The magnifying power of a compound microscope in normal adjustment (relaxed eye) is given by: M = L f_o D f_e where L is the tube length, f_o is the focal length of the objective, f_e is the focal length of the eyepiece, and D is the least distance of distinct vision. Substituting the given values: 200 = L 1.5 25 5.0 200 = L 1.5 5 L = 200 1.5 5 L = 40 1.5 = 60 cm Answer: 60 cm

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