Physics 1029A/B Chapter 6: Magnetism

A current of 15 A exists in a copper (Cu) wire
which has a diameter of 4 mm.
What is the current density? Each atom of copper has one conductionband, and
the average thermal speed √((k T)/m)
of an
electron is 1 × 106 m/s . The mass den-
sity of Cu is 8.92 g/cm3, its molar mass
is 63.5 g/mol, and Avogadro’s number is
6.02214 × 1023 atoms/mole. The electron
mass is 9.10939 × 10−31 kg, and the resistivity
of copper is 1.7 × 10−8
· m.
charge density is 1.193662073e+06