I thought it would be a good academic exercise for us to do the calculation:

Let's imaging a notional conductor, a cylindrical piece of wire.

Its cross-sectional area is A, the length is d and there are n charge carriers, e, moving at velocity v.

Therefore the total mobile charge, Q, in the cable is given by Adne

Time, t, for this charge to move along the conductor = d/v

Since current, I, = Q/t we can substitute for the above:

I = Adne / d/v = Avne

So v = I / Ane

Now i need some numbers for my notional copper wire including - number of charge carriers etc...

Who would like to take up the baton...

So if we take the cross sectional area A = 0.003m, velocity v = 1 m/s, number of charge carriers n (in copper) = 8.5 x 10

^{28} per m

^{3}. Then we need d to derive the volume of the wire to proceed. If we just assume it is 1 cubic metre anyway this simplifies things. Electron charge is 1.6 x 10

^{-19}C. So now we have the figures to calculate current and subsequently drift velocity. Then all we need do is change the value for current to see how this affects drift velocity. We could even calculate a hypothetical current needed to bring drift velocity close to c, just for fun.