A long straight copper wire, of circular cross section, contains n conduction electrons per unit volume, each of charge q. Show that the current I in the wire is given by I = nqvI?a2, where v is the drift velocity and a is the radius of the wire. At a radial distance r from the axis of the wire, what is the direction of the magnetic field B due to the current I? Assuming that magnitude of the field is B = ?10I/2I?r (r ?Y a), obtain an expression for the Lorentz force F on an electron moving with the drift velocity at the surface of the wire. If I = 10 A and a = 0.5 mm, calculate the magnitude of
(a) The drift velocity and
(b) The force, given that for copper, n = 8.5 x 1028 m–3.