Question

The focal length of the objective of a compound microscope if f_o and its distance from the eyepiece is L. The object is placed at a distance u from the objective. For proper working of the instrument,
(a) L < u
(b) L > u
(c) f_o < L < 2f_o
(d) L > 2f_o

Answer 1

(b) L > u
(d) L > 2f₀

In a compound microscope, the objective lens of a short focal length, f_o, is used. The focal length of the objective lens is less than the focal length of the eyepiece, f_​e, .The object is placed at a distance slightly greater than its focal length. The real, inverted image of the object forms somewhere in front of the eyepiece at a distance less than its focal length. This image acts as its object and the final image forms in between length, L, of the microscope. Please check and correct.
∴ L > f_o​+ f_e > 2f_o​
Also,
L > u