A microscope consistsof two convex lenses of focal lengths 2cm and 5cm placed 20cm apart. Where must the object be placed so that the final virtual image is at a distance of 25cm from the eye?

A microscope consistsof two convex lenses of focal lengths 2cm and 5cm

1.	A microscope consistsof two convex lenses of focal lengths 2cm and 5cm placed 20cm apart. Where must the object be placed so that the final virtual image is at a distance of 25cm from the eye?
Answer» Solution :For the eyepiece, FOCAL LENGTH `f=f_e=+5cm` `v=v_e=-25cm, U=u_e` substituting in `1/f=1/v-1/u implies 1/5=1/(-25)-1/u_e,1/u_e=-1/25 -1/5 =-6/25` `u_e=25/6 cm` object for the eyepiece is to be at a DISTANCE of `25/6cm` to its left But `V_0+u_e=20cm` where `u_c=25/6cm` , `v_0=20-u_e=20-25/6=95/6 cm` For the objective `v=v_0=+ 95/6 cm` `f=f_0=+2cm, u=? 1/f=1/v-1/u,1/2=6/95-1/u` `1/u= 6/95 -1/2= -83/190, u= -190/83=-2.29cm` The object is to be PLACED at a distance of 2.29cm to the left side of the objective.