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Dispersive powers of materials used in l...

Dispersive powers of materials used in lenses of an achromatic doublet are in the ratio`5:3`.If the focal length of concave lensis `15`cm,then the focal length of the other lens will be-
`(1)=-9cm (2)+9cm (3)-12cm,(4)+12cm`

Text Solution

Verified by Experts

`(f)/(f')=-(omega)/(omega')`
but `(omega)/(omega')=(5)/(3)`and `f=-15cm`
`:.f^(')=-f((omega')/(omega))=+15xx(3)/(5)=9cm`
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