Page 23 - Fiber Optic Communications Fund

4 Fiber Optic Communications

S 1

Gunman

S 2

Figure 1.3 Divergence of bullet flow.

S N I H
N
S
I L 1
H
N
S
S
N
L 2
(a) (b)

Figure 1.4 (a) Direct current-induced constant magnetic field. (b) Ampere’s circuital law.

unit positive magnetic charge (note that an isolated magnetic charge q does not exist without an associated
m
−q ), just like the electric field intensity E is defined as the force experienced by a unit positive electric charge.
m
Consider a closed path L or L around the current-carrying conductor, as shown in Fig. 1.4(b). Ampere’s
1
2
circuital law states that the line integral of H about any closed path is equal to the direct current enclosed by
that path,
H ⋅ dL = H ⋅ dL = I. (1.13)
∮ ∮
L 1 L 2
The above equation indicates that the sum of the components of H that are parallel to the tangent of a closed
curve times the differential path length is equal to the current enclosed by this curve. If the closed path is a
circle (L ) of radius r, due to circular symmetry, the magnitude of H is constant at any point on L and its
1
1