An electron of mass m moving with initial velocity v→=v0i^+v0j^ is in an electric field E→=−E0k^. If λ0 is initial de-Broglie wavelength of electron, its de-Broglie wave length at time t is given by:

Electric force on electron due to the electric field is,F→=ma→=eE→For velocity, using vf=u+at⇒v→f=v0i^+v0j^+−eE0mtk^vf→=2v02+e2E2m2t2Now applying equation for de-broglie wavelength,λ=hm2v02+e2E02m2t2λ=λ01+e2E022m2v02t2