An electron with mass ' m ' with an initial velocity (\mathrm{t}=0) \overrightarrow{\mathrm{v}}=\mathrm{v}_0 \hat{i}\left(\mathrm{v}_0>0\right) enters a magnetic field \overrightarrow{\mathrm{B}}=\mathrm{B}_0 \hat{j}. If the initial de-Broglie wavelength at \mathrm{t}=0 is \lambda_0 then its value after time ' t ' would be :