i am really really confused . I know what Drift velocity is but the problem is I have three Sources which tell absolutely different expression for drift velocity and I cat relate . please tell which is right . This website and MIT Profs. Walter Lewin In his Lectures says Vd = eE/m x (Tau) http://hyperphysics.phy-astr.gsu.edu/hbase/electric/ohmmic.html And my book says Vd = eE/2m x (Tau) Thats Ridiculous Heres the proof What the heck is goin on ?