Question

The focal lengths of the eyepiece and the objective of a compound
microscope are 5 cm and 1 cm respectively and the length of the tube
is 20 cm. Calculate the magnifying power of the microscope, when
the final image is formed at infinity. The value of least distance of
distinct vision is 25 cm.
(A) 70
(B) 90
(C) 95
(D) 75​

Answer 1

Answer:

70

Explanation:

Solution :

Here, fe=5cm,f0=1cm,L=20cm,m=?

ve=∞,d=25cm

As final image is at infinity, image formed by objective lies at the focus of eye piece.

∴v0=L−fe=20−5=15cm

From 1u0=1v0−1f0=115−11=−1415

u0=−1514cm

As final image is at infinity,

∴m=v0u0(dfe)=1515/14×255=70.