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 $
