Optics Question 619

Question: The dispersive powers of glasses of lenses used in an achromatic pair are in the ratio 5 : 3. If the focal length of the concave lens is 15 cm, then the nature and focal length of the other lens would be

[MP PET 1997]

Options:

A) Convex, 9 cm

B) Concave, 9 cm

C) Convex, 25 cm

D) Concave, 25 cm

Show Answer

Answer:

Correct Answer: A

Solution:

$ \frac{{\omega _{1}}}{{\omega _{2}}}=-\frac{f _{1}}{f _{2}}\Rightarrow \frac{5}{3}=\frac{-(-15)}{f _{2}}\Rightarrow f _{2}=9 $$ cm $



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