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 $



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