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Can we apply Newton law’s to the motion of electrons? Note: In this explanation, the random motion of electrons is neglected. Let us consider a conductor of length l and cross sectional area A. Let n be the density of electrons of a conductor. The current passing through the conductor when the ends of the conductor is maintained at a constant potential difference V is given by I = nAevds ....................... (a) Where e is the charge of electron and vd is the drift velocity of electrons. Work done by the source to move electron between the ends (along the conductor) is given by, W = Ve ....................... (b) We know that the work done by the electric force, W =Fl ....................... (c) Where F is the force applied by the electric field. From equations (b) and (c), We get Fl = Ve => F = Ve/l From Newton’s second law, we know that F = ma is applicable to any particle. Hence we have, ma = Ve/l D a = Ve/lm ......................(d) Assuming that the initial velocity (u) of electron is zero. Let v velocity acquired by the electron in a time interval τ (interval between successive collisions). Then u = 0 and t = τ From equation v = u+at v = aτ = Veτ/lm (from equation d) Due to collisions with lattice ions, the motion of electrons is restricted. Hence the average velocity of electron in time τ becomes its drift velocity. Average velocity of electron vd= (v+u)/2 = v/2 Substituting the value of v in above equation, we get |