Optics Question 618

Question: Two lenses have focal lengths $ f _{1} $ and $ f _{2} $ and their dispersive powers are $ {\omega _{1}} $ and $ {\omega _{2}} $ respectively. They will together form an achromatic combination if

Options:

A) $ {\omega _{1}}f _{1}={\omega _{2}}f _{2} $

B) $ {\omega _{1}}f _{2}+{\omega _{2}}f _{1}=0 $

C) $ {\omega _{1}}+f _{1}={\omega _{2}}+f _{2} $

D) $ {\omega _{1}}-f _{1}={\omega _{2}}-f _{2} $

Show Answer

Answer:

Correct Answer: B

Solution:

For achromatic combination, $ \frac{w _{1}}{f _{1}}+\frac{w _{2}}{f _{2}}=0 $

Therefore $ w _{1}f _{2}+w _{2}f _{1}=0 $



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