Question -
Answer -
Focal length of the objective lens,
= 1.25 cm
Focal length of the eyepiece, fe = 5 cm
Least distance of distinct vision, d =25 cm
Angular magnification ofthe compound microscope = 30X
Total magnifying power of the compoundmicroscope, m = 30
Theangular magnification of the eyepiece is given by the relation:The angular magnification of the objectivelens (mo) is related to me as:
= m
Applying the lens formulafor the objective lens:
The object should beplaced 1.5 cm away from the objective lens to obtain the desired magnification.
Applying the lens formulafor the eyepiece:
Where,
= Image distance for the eyepiece = −d =−25 cm
= Object distancefor the eyepiece
Separation between the objective lens and theeyepiece 
Therefore,the separation between the objective lens and the eyepiece should be 11.67 cm.