Find the length of a microscope having magnifying power 100, if the focal lengths of the objective and eye piece are 2 cm and 5 cm respectively. Assume that the final image is formed at infinity

   L = 40 cm

Explanation:

A microscope is an optical instrument built by two lenses in such a way that the image of the first is formed within the distance of the other (eyepiece), so that the latter creates an enlarged virtual image of the object, for which the magnification of the microscope is the same to the multiplication of the magnification of each lens

    M = - L / f₀ (25 cm /)

where fo and fe are the focal lengths of the objective and eyepiece, 25 cm is the near vision distance and L is the length of the microscope

     L = - M f_{o} f_{e} / 25

let's calculate

     L = - (-100) 2 5/25

      L = 40 cm