Page 7 - Electrical Equipment Handbook _ Troubleshooting and Maintenance

FUNDAMENTALS OF ELECTRIC SYSTEMS

1.6 CHAPTER ONE

FIGURE 1.4 Lines of B near a long, circular cylindrical wire. A
current i, suggested by the central dot, emerges from the page.

THE MAGNETIC FIELD

A magnetic field is defined as the space around a magnet or a current-carrying conductor.
The magnetic field B is represented by lines of induction. Figure 1.4 illustrates the lines of
induction of a magnetic field B near a long current-carrying conductor.
The vector of the magnetic field is related to its lines of induction in this way:
1. The direction of B at any point is given by the tangent to the line of induction.
2. The number of lines of induction per unit cross-sectional area (perpendicular to the
lines) is proportional to the magnitude of B. Magnetic field B is large if the lines are
close together, and it is small if they are far apart.
The flux
of magnetic field B is given by
B

B
dS
B
The integral is taken over the surface for which
is defined.
B
The magnetic field exerts a force on any charge moving through it. If q is a positive
0
charge moving at a velocity v in a magnetic field B, the force F acting on the charge
(Fig. 1.5) is given by
F q v B
0
The magnitude of the force F is given by
F q vB sin
0
where is the angle between v and B.

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