Optics Question 342
Question: If the focal length of objective and eye lens are 1.2 cm and 3 cm respectively and the object is put 1.25 cm away from the objective lens and the final image is formed at infinity. The magnifying power of the microscope is
Options:
A) 150
B) 200
C) 250
D) 400
Show Answer
Answer:
Correct Answer: B
Solution:
$ {m _{\infty }}=-\frac{v _{o}}{u _{o}}\times \frac{D}{f _{e}} $ From $ \frac{1}{f _{o}}=\frac{1}{v _{o}}-\frac{1}{u _{o}} $
$ \Rightarrow \frac{1}{(+1.2)}=\frac{1}{v _{o}}-\frac{1}{(-1.25)} $
$ \Rightarrow v _{o}=30\ cm $
$ \therefore |{m _{\infty }}|\ =\frac{30}{1.25}\times \frac{25}{3}=200 $
