Posted by kabelo on .
a copper wire has a diameter of 1.02mm,the wire carries a constant current of 1.67A,the density of the free electrons is 8.5X10^28 e/m^3.calculate the current density and drift velocity

phys102 
drwls,
(density)*(area)*(drift velocity)*(electron charge) = current, in Amperes.
Solve for the drift velocity, which will probaby be slow.
Current density is (total current)/(area)
The "area" in both cases is pi*D^2/4, and should be expressed in square meters. 
phys102 
Aysah,
A copper wire has a diameter dCu = 0.0517 cm, is L = 2.85 m long, and has a density of charge carriers of 8.50·1028 electrons/m3. As shown in the figure, the copper wire is attached to an equal length of aluminum wire with a diameter dAl = 0.0267 cm and density of charge carriers of 6.02·1028. A current of 0.400 A flows through the copper wire.
a) What is the ratio of the current densities in the two wires, JCu/JAl?
b) What is the ratio of the drift velocities in the two wires, vdCu/vdAl?