Mean drift velocity of a conduction electron in copper.

[Minakami]

Homework Statement

Estimate the mean drift velocity of a conduction electron in copper, assuming that there is one conduction electron per atom. Consider No. 14 wire (diamter 0.16 cm), common in houses, carrying 5A. The result should be very small. Why then does an electric light turn on almost instantly when you flip the switch?

Homework Equations

I = qn_Lv_d=nAqv_d

The Attempt at a Solution

Density of copper = 8.94 g/cm³
Molar mass = 63.546 g/mol

amount of copper per cubic cm:
Density/Molar mass = 0.14068 mol/cm³ = 8.47 x 10²² atoms/cm³

so

v_d = I/nAq = (5 A) / (8.47 x 10²² atoms/cm³)(pi * 0.08 cm)²(1.609 x 10^-19 C)
= 0.018 cm/s



Did I do this correctly? And I have no idea about the second question...

 

[Stonebridge]

Your calculation is fine and the answer is about what I would expect.
The electron drift velocity is very slow, but they move in response to the applied electric field. The field is transmitted through the wire at the speed of light.