When a charged particle is accelerated through $1.5 \mathrm{volts}$ its de-Broglie wavelength is ${\lambda }_1$ and it is ${\lambda }_2$ when the same particle is accelerated through $13.5 \mathrm{volts}$. The ratio $\frac{{\lambda }_1}{{\lambda }_2}$(to the nearest integer) is_______.