Q18 of 70 Page 11

If we need magnification of 375 from a microscope of tube length 15 cm and objective of focal length 0.5 cm, what focal length of eye-piece should we use?

Magnification m = 375
Length of the tube L = 15 cm
Focal length of the objective fo = 0.5 cm
We know that
Magnification m =
                375 =
                      =
                  25 =
               25fe = 50 + 2 fe
               23fe = 50
      fe = 50/23 = 2.17 cm.

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16 When is a person said to have developed cataract in his eye? How is the vision of a person having cataract restored? 17 Where should an object be placed in front of a convex lens so as to use it as a simple microscope? 19 If focal length of the objective and eye-piece of a telescope are 10 cm and 4 cm respectively, what will be its magnifying power in
(i) normal adjustments,
(ii) adjustment where image of distance object is formed at D? Given D = 25 cm. 20 Which of the two, objective or eye-piece, of a telescope has a large aperture? Give reason for your answer.