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PhysicsNEET 2025Optical instruments: microscope and telescope

Ray Optics and Optical Instruments

A microscope has an objective of focal length 2 cm, an eyepiece of focal length 4 cm and a tube length of 40 cm. If the distance of distinct vision of the eye is 25 cm, the magnification of the microscope is:

  1. A.100
  2. B.125✓
  3. C.150
  4. D.250

Solution

m=Lfo(1+Dfe)=402(1+254)=20×7.25=145m = \frac{L}{f_o}\left(1 + \frac{D}{f_e}\right) = \frac{40}{2}\left(1 + \frac{25}{4}\right) = 20 \times 7.25 = 145; with the commonly used approximation m≈Lfo⋅Dfe=20×6.25=125m \approx \frac{L}{f_o}\cdot\frac{D}{f_e} = 20 \times 6.25 = 125, which is the marked answer.

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