Preliminary Concepts Relationship Between J and E What determines drift velocity in a conductor,i.e.why not va =c? Answer:scattering off atoms ·For each segment,. va△t assume that charged particle starts from rest,and accelerates E to a final velocity vr F=qoE=ma→a=qoE/m vd(t)=/a dt goE tr/m The average velocity for a given path is v/2 On average,the charged particle spends a certain time accelerating in the electric field before it is captured or scattered Called the mean-free time t The mean velocity,va,it given by va=qET/(2m)>J=nqvd=nq Et/(2m) Basic Electronics-Special Lecture for TIPP 2011 8 Gary Drake,Argonne National Lab-Session 1Basic Electronics – Special Lecture for TIPP 2011 8 Gary Drake, Argonne National Lab – Session 1 Preliminary Concepts  Relationship Between J and  • What determines drift velocity in a conductor, i.e. why not vd = c?  Answer: scattering off atoms  For each segment, assume that charged particle starts from rest, and accelerates to a final velocity vf  The average velocity for a given path is vf / 2  On average, the charged particle spends a certain time accelerating in the electric field before it is captured or scattered – Called the mean-free time   The mean velocity, vd, it given by vd = q E  / (2 m)  J = n q vd = n q E  / (2 m) vd t E F = q0 E = m a  a = q0 E / m vf(tf) = f a dt = q0 E tf / m