The total magnification produced by a compound microscope is 20. The magnification produced by eyepiece alone in 5. The microscope is focussed on certain object. The distance between object and eyepiece is observed to be 14 cm. If the least distance of distinct vision is 20 cm.
Overall magnification
m=mome=(Lfo)(Dfe)=20
Dfe=5
hence
Lf0=4
But D=20;
hence focal length of eye piece fe=4 cm
Distance between objective and eyepiece=f0+L+fe=f0+4f0+fe=14 cm
Hence focal length of objective, f0=2 cm
Here it is assumed that the image of objective lens is formed near to focal point of eyepiece.