A stream of a positively charged particles having $\frac{\mathit{q}}{\mathit{m}}=2\times {10}^{11} \mathrm{C} {\mathrm{kg}}^{-1}$ and velocity ${\overrightarrow{\mathrm{v}}}_0=3\times {10}^7 \hat{i} \mathrm{m} {\mathrm{s}}^{-1}$ is deflected by an electric field $1.8\hat{j} \mathrm{kV} {\mathrm{m}}^{-1}$. The electric field exists in a region of $10 \mathrm{cm}$ along $x$ direction. Due to the electric field, the deflection of the charge particles in the $y$ direction is _____  $\mathrm{mm}$.