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