
Principles of Analog Electronics
138
Observation
Whenever electrons ow through an inductor, the magnetic eld that will
develop around that inductor can have considerable strength. So, it is believed
that some illusionists use such magnetic elds to create the illusion of levita-
tion (Figure 4.68).
4.7.5.2 Coaxial
Consider a coaxial inductor, as represented in
Figure4.69.
We have an inner conducting cylinder of radius a,
an outer conducting cylinder of radius b > a, and their
length l. The magnetic ux loop, which is along the inner
cylinder and closes along the outer one, results in
BdS
li
r
dr
li b
a22
ln
B
b
∫∫
Φ= =
µ
=
µ
Therefore, the inducta ...