09D806A450335B1B0D3E920D941BEF21A3A75107_Electrodynamics-3(1).pdf

電磁學

1. Electrodynamics
JesonChen,
Fu Jen University

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5. Fundamental Postulates of Electrostatics in Free Space

f 위프 = 그 $, pd. which states that the total outward flux of the elec-
y eo YY tric field intensity over any closed surface in free

space is equal to the total charge

Gauss's law enclosed in the surface divided by 06.

of free space eo x 107? (F/m).

6. Fundamental Postulates of Electrostatics in Free Space

which asserts that the scalar line integral of

the static electric field intensity
around any closed path vanishes.

Thus Eq. (3-8) is an expression of Kirchhoff’s voltage
law in circuit theory that the algebraic sum

Vi = -/gra
으 of voltage drops around any closed circuit

14. Coulomb’s Law

The permittivity of air is essentially the same as that of the free space. The
factor 1/(4ne,) appears very frequently in electrostatics. From Eq. (1-11) we know
that eo = 1/(c7o) But zo = 42 x 107” (H/m) in SI units; so

1 ーー Hoc?

= 一 -一 一 10-7c2 es
nes ~ 07e (m/F) (3-16)

exactly. If we use the approximate value c = 3 x 10% (m/s), then 1/(4re,) = 9 x

10° (m/F).