Question

A compound microscope has lenses of focal length 1.0cm and 5.0cm . An object is placed 1.2cm from the objective lens . If a virtual image is formed 25cm from the eyepiece , calculate the distance between the two lenses

Answer 1

1) Using the lens formula for image q formed by the objective.
1/f_o =1/p+1/q
1/1=1/1.2+1/q
q=6 cm.
2) Now, this image will act as an object for second lens i.e. eyepiece. Using the lens formula for the distance p_1 from the eyepiece.
1/f_e =1/p_1 +1/q_1
1/5=1/p_1 +1/(-25)
p_1=4.2 cm.
3) The distance between the two lenses:
L=6+4.2=10.2 cm.