Focal length of a convex lens made of crown glass is $$20$$ cm. An achromatic lens is to be made by keeping two lenses, one made of crown glass and the other made of flint glass, in contact with each other. If dispersive power of crown glass is $$0.016$$ and that of flint glass is $$0.03$$, find the focal length of the lens made of flint glass.

Question

Infinity Learn · Accepted Answer

For achromatic combination, ω$$f+$$ω'f'$$=0$$⇒f'$$=-f$$ω'ω$$=-20$$ x $$0.030.016cm=-37.5$$ cm

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