1. The problem statement, all variables and given/known data The figure shows wire section 1 of diameter 4R and wire section 2 of diameter 2R, connected by a tapered section. The wire is copper and carries a current. Assume that the current is uniformly distributed across any cross-sectional area through the wire's width. The electric potential change V along the length L = 1.95 m shown in section 2 is 13.5 µV. The number of charge carriers per unit volume is 8.49x10^28 m-3. What is the drift speed of the conduction electrons in section 1? 2. Relevant equations v = j/nq j=E/p = v/pL 3. The attempt at a solution I got J2 using the provided v2 and p ( of copper = 1.72e-8) and the L2 J2 = (13.5e-6)/(1.72e-8)(1.95) = 402.5 A/m^2 Then I used the relation between the two sections > J1A1 = J2A2 >>> J1(0.25Pi 4^2 ) = J2(0.25Pi 2^2) >>> j1 = 100.625 A/m^2 The drift speed of sec 1 would be >>> V1 = J1 / nq = 100.625/(8.49e28)(1.6e-19) = 7.41e-9 m/s ( which was a wrong answer ) what is my mistake ?