
Nature of Matter
81
cm
3.62 10
8.410
8
3
22
3
×
≅×
−
as carriers in the valence band (Figure 3.23).
When an electric voltage is applied across a conductor
wire, the free electrons move in the direction imposed
by the related electric eld, so creating a ow of charges,
that is, an electric current.
To understand where the free electrons are in a con-
ductor, it is convenient to refer to Gauss’s law (Johann
Carl Friedrich Gauss, German mathematician and sci-
entist, 1777–1855, Figure 3.24), also known as Gauss’s
ux theorem, which states that the electric eld within a
spherical surface uniformly charged is null (Figure 3.25).
Considering that the ...