
Principles of Analog Electronics
76
3.5 ENERGY BAND THEORY
The energy band theory provides an interest-
ing explanation of the behavior of electrons
in solids. To do an analysis, at least qualita-
tively, the analogy of the vibrant rope phe-
nomenon is applicable. Given an elastic rope
with length l, if we imagine it xed at its ends,
we can make it vibrate only with frequen-
cies f that satisfy the condition
,
where n is an integer, seen in Figure 3.12.
Considering
=
=
f
v
v
n
(where n = 1, 2, 3...) means that, in a xed
transmission medium, f is proportional to
the value
n
f
n
∝
Therefore, the rope essentially can vibrate
only w