Question

If the refractive indices of crown glass for red, yellow and violet colours are respectively ${\mu }_r,{\mu }_y,{\mu }_v$, then the dispersive power of this glass would be

• A. $\frac{{\mu }_v-{\mu }_r}{{\mu }_y-1}$
• B. $\frac{{\mu }_v-{\mu }_y}{{\mu }_r-1}$
• C. $\frac{{\mu }_v-{\mu }_y}{{\mu }_y-{\mu }_r}$
• D. $\frac{{\mu }_v-{\mu }_r}{{\mu }_y}-1$

Answer 1

The correct option is A $\frac{{\mu }_v-{\mu }_r}{{\mu }_y-1}$

Dispersive power of a glass is given by ratio of difference of reflective index of two extreme wavelength to the difference of intermediate wavelength to unity i.e.

$DispersivePower=\frac{{\mu }_v-{\mu }_r}{{\mu }_y-1}$