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 $
