An electron (mass $m$) with an initial velocity $\vec{v} = v_0 \hat{i} (v_0 > 0)$ is moving in an electric field $\vec{E} = -E_0 \hat{i} (E_0 > 0)$ where $E_0$ is constant. If at $t = 0$, de-Broglie wavelength is $\lambda_0 = \frac{h}{mv_0}$, then its de-Broglie wavelength after time $t$ is given by