Question

You are given two converging lens of focal length 1.25 cm and 5 cm

Answer 1

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Question :

You are given two converging lenses of focal lengths 1.25 cm and 5 cm to design a compound microscope. if it is desired to have a magnification of 30, find out the separation between the objective and the eyepiece.

Answer :

Given,

f₀ = 1.25 cm , fe = 5 cm ( In microscope, focal length of objective lens should be very small )

Magnification,                  m = 30,

If we set these lens for minimum distance for distinct vision, then for

           m = L/f₀ ( 1 + D/fe )

   30 = L/1.25 ( 1 + 25/5 )

   L = 1.25 × 30 × $\frac{5}{30}$

   L = 5 × 1.25

   L = 6.25 cm

Hence, distance between two lenses is

              =  f₀ + 6.25 + fe

              = 1.25 + 6.25 + 5

              = 12.5 cm

This is required separation between the objective and the eyepiece.

GOOD LUCK !!