A particle $\mathrm{A}$ of mass $m$ and charge $q$ is accelerated by a potential difference of $50\mathrm{ }\mathrm{V}.$ Another particle $\mathrm{B}$ of mass $4m$ and charge $q$ is accelerated by a potential difference of $2500\mathrm{ }\mathrm{V}.$ The ratio of de-Broglie wavelengths $\frac{{\lambda }_A}{{\lambda }_B}$ is close to: