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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-co




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.
$${A}\:{concave}\:{lens}\:{of}\:{focal}\:{length}\:\mathrm{60}{cm} \\ $$$${is}\:{made}\:{of}\:{material}\:{whose} \\ $$$${refractive}\:{index}\:{for}\:{red}\:{light}\:{is} \\ $$$$\mathrm{1}.\mathrm{641}\:{and}\:{refractive}\:{index}\:{for}\:{blue} \\ $$$${light}\:{is}\:\mathrm{1}.\mathrm{659}.{That}\:{for}\:{white}\:{light} \\ $$$${is}\:\mathrm{1}.\mathrm{65}.{It}\:{is}\:{combined}\:{with}\:{a}\:{convex} \\ $$$${lens}\:{of}\:{dispersive}\:{power}\:\mathrm{0}.\mathrm{0173}\:{to} \\ $$$${form}\:{an}\:{achromatic}\:{doublet}. \\ $$$${Calculate}\:{the}\:{focal}\:{length}\:{of}\:{the} \\ $$$${achromatic}\:{lens}. \\ $$
Commented by Necxx last updated on 15/Aug/18
please help
$${please}\:{help} \\ $$

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