ray_optics microscope_and_telescope Question 120
Question: A compound microscope has an eye piece of focal length 10 cm and an objective of focal length 4 cm. Calculate the magnification, if an object is kept at a distance of 5 cm from the objective so that final image is formed at the least distance vision (20 cm) [UP SEAT 2005]
Options:
A) 12
B) 11
C) 10
D) 13
Answer:
Correct Answer: A
Solution:
For objective lens $ \frac{1}{f_{o}}=\frac{1}{v_{o}}-\frac{1}{u_{o}} $
Þ $ \frac{1}{v_{o}}=\frac{1}{f_{o}}+\frac{1}{u_{o}} $ $ =\frac{1}{4}+\frac{1}{-5}=\frac{1}{20} $
Þ $ v_{o}=20cm $ Now $ M=\frac{v_{o}}{u_{o}}( 1+\frac{D}{f_{e}} ) $ $ =\frac{20}{5}( 1+\frac{20}{10} ) $ $ =12,. $
BETA
