A microscope has an objective of 10 mm focal length and an eyepiece of 25 mm focal length. What is the distance between the lenses, if the object is in sharp focus when it is 10.5 mm from the objective?
Correct answer: B. 235 mm
- A. 115 mm
- B. 235 mm
- C. 417 mm
- D. 716 mm
- E. 617 mm
Explanation
The correct answer is 235 mm. To find the distance between the lenses, use the formula: 1/f = 1/v - 1/u for the objective lens, where f is the focal length of the objective lens, u is the distance of the object from the lens, and v is the image distance. For the given microscope, f = 10 mm, and u = 10.5 mm. Solving for v, we get v = 210 mm. The total length of the microscope, which is the sum of v and the focal length of the eyepiece (25 mm), gives us 235 mm. The other options are incorrect due to errors in applying the lens formula or arithmetic mistakes in the calculations.
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Light is studied through reflection, refraction, dispersion, interference, diffraction and polarization, linking ray behavior with its wave nature. Questions may involve mirrors, lenses, optical instruments, refractive index and image formation, while geometrical optics deals with rays and wave optics explains effects such as interference and diffraction.
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