Question Number 41906 by Necxx last updated on 15/Aug/18
$${A}\:{concave}\:{lens}\:{of}\:{focal}\:{length}\:\mathrm{60}{cm} \\ $$$${is}\:{made}\:{of}\:{material}\:{whose} \\ $$$${refractive}\:{index}\:{for}\:{red}\:{light}\:{is} \\ $$$$\mathrm{1}.\mathrm{641}\:{and}\:{refractive}\:{index}\:{for}\:{blue} \\ $$$${light}\:{is}\:\mathrm{1}.\mathrm{659}.{That}\:{for}\:{white}\:{light} \\ $$$${is}\:\mathrm{1}.\mathrm{65}.{It}\:{is}\:{combined}\:{with}\:{a}\:{convex} \\ $$$${lens}\:{of}\:{dispersive}\:{power}\:\mathrm{0}.\mathrm{0173}\:{to} \\ $$$${form}\:{an}\:{achromatic}\:{doublet}. \\ $$$${Calculate}\:{the}\:{focal}\:{length}\:{of}\:{the} \\ $$$${achromatic}\:{lens}. \\ $$
Commented by Necxx last updated on 15/Aug/18
$${please}\:{help} \\ $$