1.

The dispersive powers of crown and flint glasses are `0.02` and `0.04` respectively. In an achromatic combination of lenses the focal length of flint glass lens is `40 cm`. The focal length of crown glass lens will beA. `-20 cm`B. `+20 cm`C. `-10cm`D. `+10 cm`

Answer» Correct Answer - A
By using `(omega_(1))/(f_(1))+(omega_(2))/(f_(2))=0implies(0.02)/(f_(1))+(0.04)/(40)=0`
`f_(1)=-20cm`


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