An electron (mass $\mathrm{m}$) with an initial velocity $\vec{v}=v_{0} \hat{i}\left(v_{0}>0\right)$ is moving in an electric field $\vec{E}=-E_{0} \hat{i}\left(E_{0}>0\right)$ where $E_{0}$ is constant. If at $\mathrm{t}=0$ de Broglie wavelength is $\lambda_{0}=\frac{h}{m v_{0}}$, then its de Broglie wavelength after time t is given by