Fundamentals of Materials Science and Engineering: An Integrated Approach, 3e

GTBL042-18 GTBL042-Callister-v2 October 5, 2007 17:39

2nd Revise Page

724 • Chapter 18 / Magnetic Properties

N

S

Figure 18.1 Magnetic field lines of force around a current

loop and a bar magnet.

is the way in which a magnetic compass needle lines up with the earth’s magnetic

field.

Magnetic Field Vectors

Before discussing the origin of magnetic moments in solid materials, we describe

magnetic behavior in terms of several field vectors. The externally applied magnetic

magnetic field field, sometimes called themagnetic field strength,is designated byH. If the magnetic

strength field is generated by means of a cylindrical coil (or solenoid) consisting ofNclosely

spaced turns, having a lengthl, and carrying a current of magnitudeI, then

H=

NI

l

(18.1)

Magnetic field

strength within a

coil—dependence on

number of turns,

applied current, and

coil length A schematic diagram of such an arrangement is shown in Figure 18.3a. The magnetic

field that is generated by the current loop and the bar magnet in Figure 18.1 is anH

field. The units ofHare ampere-turns per meter, or just amperes per meter.

magnetic induction Themagnetic induction,ormagnetic flux density,denoted byB, represents the

magnetic flux density magnitude of the internal field strength within a substance that is subjected to anH

field. The units forBare teslas [or webers per square meter (Wb/m^2 )]. BothBand

Hare field vectors, being characterized not only by magnitude, but also by direction

in space.

N

S

Figure 18.2 The magnetic moment as designated by an arrow.