Page 248 - Engineering Electromagnetics, 8th Edition

8 CHAPTER

Magnetic Forces,

Materials, and

Inductance

e are now ready to undertake the second half of the magnetic field problem,
that of determining the forces and torques exerted by the magnetic field on
W other charges. The electric field causes a force to be exerted on a charge
that may be either stationary or in motion; we will see that the steady magnetic field is
capable of exerting a force only on a moving charge. This result appears reasonable; a
magnetic field may be produced by moving charges and may exert forces on moving
charges; a magnetic field cannot arise from stationary charges and cannot exert any
force on a stationary charge.
This chapter initially considers the forces and torques on current-carrying con-
ductors that may either be of a filamentary nature or possess a finite cross section
with a known current density distribution. The problems associated with the motion
of particles in a vacuum are largely avoided.
With an understanding of the fundamental effects produced by the magnetic
field, we may then consider the varied types of magnetic materials, the analysis
of elementary magnetic circuits, the forces on magnetic materials, and finally, the
important electrical circuit concepts of self-inductance and mutual inductance. ■

8.1 FORCE ON A MOVING CHARGE
In an electric field, the definition of the electric field intensity shows us that the force
on a charged particle is

F = QE (1)

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