A long straight copper wire, of circular cross ection, contains n conduction electrons per unit volume, each of charge q. Show that the current l in the wire is given by
`l = nqv pi a^(2)`
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 l? Assuming that the magnitude of the field is `B = mu_(0)l//2pir(r ge a)`, obtain an expression for the Lorentz force F on an electron moving with the drift velocity at the surface of the wire.
If `l = 10` A and a = 0.5mm, calcualte the magnitude of (a) the drift velocity and (b) the forcce, given that for copper, `n = 8.5 xx 10^(28) m^(-3)`

Explanation

(a) `9.4 xx 10^(-4)m//s`
(b) `6.0 xx 10^(-25) N`