Question

If the refractive indices of crown glass for red, yellow and violet colours are respectively ${\mu }_r,{\mu }_y$ and ${\mu }_v$, 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 $\frac{{\mu }_v-{\mu }_r}{{\mu }_y-1}$


For small A and

For violet :


For red:


For yellow:


Dispersive power of prism

Putting expressions as derived above,

Therefore,