A concave lens of focal length 60cm is made of material whose refractive index for red light is 1.641 and refractive index for blue light is 1.659.That for white light is 1.65.It is combined with a convex lens of dispersive power 0.0173 to form an achromatic doublet. Calculate the focal length of the achromatic lens.


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Question Number 41906 by Necxx last updated on 15/Aug/18
$A concave lens of focal length 60cm is made of material whose refractive index for red light is 1.641 and refractive index for blue light is 1.659.That for white light is 1.65.It is combined with a convex lens of dispersive power 0.0173 to form an achromatic doublet. Calculate the focal length of the achromatic lens.$
$A c o n c a v e l e n s o f f o c a l l e n g t h 60 c m$ $i s m a d e o f m a t e r i a l w h o s e$ $r e f r a c t i v e i n d e x f o r r e d l i g h t i s$ $1.641 a n d r e f r a c t i v e i n d e x f o r b l u e$ $l i g h t i s 1.659 . T h a t f o r w h i t e l i g h t$ $i s 1.65 . I t i s c o m b i n e d w i t h a c o n v e x$ $l e n s o f d i s p e r s i v e p o w e r 0.0173 t o$ $f o r m a n a c h r o m a t i c d o u b l e t .$ $C a l c u l a t e t h e f o c a l l e n g t h o f t h e$ $a c h r o m a t i c l e n s .$
Commented by Necxx last updated on 15/Aug/18

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