# Dr. Naglaa Fathy Mohamed

Electronics - Devices

Oct 18, 2013 (4 years and 8 months ago)

246 views

1

ةيدوعسلا ةيبرعلا ةكلمملا

ةيملاسلإا دوعس نب دمحم ماملإا ةعماج

مولعلا ةيلك

ءايزيفلا مسق

KINGDOM OF SAUDI ARABIA

AL
-
IMAM MUHAMMAD BIN SAUD

ISLAMIC UNIVERSITY

FACULTY OF SCIENCES

DEPARTMENT OF PHYSICS

Dr. Naglaa
Fathy

Mohamed

Physics department

1433/1434

2

Chapter
1
:

Electrostatic Fields

Chapter
3

:
Magnetic Fields in Matter

Chapter 2
: Electric Fields in Matter

Chapter
4
:

Maxwell’s Equations

Chapter 5
:

Electromagnetic Wave Propagation

Elements of
Electromagnetics
-

Third Edition

Matthew N. O.
.

3

Chapter
3

Magnetic Field in Matter

Chapter Outline:

1
.
Volume Current Density

2
.
Biot

-

Savart’s

Law

3
.
Ampere’s Circuit Law
-
Maxwell’s Equation

4
.
Magnetic Flux Density

Maxwell’s Equation

5
.
Maxwell’s Equations for Static Electromagnetic Field

6
.
Magnetic Dipole

7
.
Magnetization in Materials

Dr.
Naglaa

fathy
. Electromagnetic Field, PHY
321

4

The
net magnetic flux
(
Wb
) through surface S
is
given by.

In
free
space, the magnetic flux density is given by:

4
-

Magnetic Flux
Density

Maxwell’s Equation

Dr.
Naglaa

fathy
. Electromagnetic Field, PHY
321

5

4
-

Magnetic Flux
Density

Maxwell’s Equation

The total flux through a closed surface in a magnetic field must be zero

o

An
isolated magnetic charge does not exist

o

Magnetic flux is conserved

By applying the divergence theorem:

Fourth Maxwell's

equation

This Equation suggests that the magnetic field lines are always continuous.

Dr.
Naglaa

fathy
. Electromagnetic Field, PHY 321

5
-

Maxwell’s Equations for Static
Electromagnetic Fields

Maxwell's four equations for
static electromagnetic fields

Maxwell's equations are only for static EM fields.

6

Dr.
Naglaa

fathy
. Electromagnetic Field, PHY 321

7

6
-

Magnetic Dipole

-

A small filamentary current loop or a bar magnet is usually referred
to as a magnetic dipole.

-

The direction of the magnetic dipole moment points from the south to
north pole of a magnet.

Dr.
Naglaa

fathy
. Electromagnetic Field, PHY 321

8

6
-

Magnetic Dipole

Magnetic field at P due to a current loop:

Magnetic dipole moment

A bar magnet is usually referred to as a
magnetic dipole.

9

7
-

Magnetization in Materials

Electron orbiting

around the nucleus

Orbital magnetic moment

Spin magnetic moments

Magnetic

Moments

of

Atoms
:

Both of these electronic motions produce internal magnetic fields B.

o

Similar to the magnetic field produced by a current loop

10

7
-

Magnetization in Materials

The magnetic dipole moment of the loop:

where S is the area of the loop and I is the bound current (bound to the atom).

Dr.
Naglaa

fathy
. Electromagnetic Field, PHY 321

11

7
-

Magnetization in Materials

Without an external magnetic field applied to
the material, the sum of magnetic dipole
moments is zero due to the random orientation.

Dr. Naglaa fathy. Electromagnetic
Field, PHY
321

12

7
-

Magnetization in Materials

When an external magnetic field is applied, the
magnetic moments of the electrons align themselves
with magnetic field so that the net magnetic moment is
not zero.

Dr. Naglaa fathy. Electromagnetic Field, PHY
321

13

7
-

Magnetization in Materials

The relation between Magnetization (M) and applied external magnetic field:

(a) Diamagnetic materials

(b) Paramagnetic materials

(c) Ferromagnetic Materials

Classification of magnetic Materials:

H

paramagnetic

H

Diamagnetic

H
=0

Ferromagnetic

Dr.
Naglaa

fathy
. Electromagnetic Field, PHY
321

Magnetic Domains:

K

L

M N

electrons in Fe atom:

Dr.
Naglaa

Fathy

Mohamed, physics department

15

7
-

Magnetization in Materials

The magnetization (in A/m
) is
:

the magnetic dipole moment per unit volume.

If there are N atoms in a given volume

A medium for which M is not zero everywhere is said to be magnetized.

Dr.
Naglaa

fathy
. Electromagnetic Field, PHY
321

16

7
-

Magnetization in Materials

The potential of a magnetic body is due to:

volume current density
J
b

throughout the body and

surface
current
K
b

on the surface of the body.

For a magnetized body

Dr.
Naglaa

fathy
. Electromagnetic Field, PHY
321

17

7
-

Magnetization in Materials

J is the free current volume density

In free space, M = 0:

Dr.
Naglaa

fathy
. Electromagnetic Field, PHY
321

18

7
-

Magnetization in Materials

Dr.
Naglaa

fathy
. Electromagnetic Field, PHY
321

19

7
-

Magnetization in Materials

m
is a dimensionless quantity
called
magnetic susceptibility
of the
medium.

o

is a measure of how susceptible (or sensitive) the material is to a

magnetic field

Dr.
Naglaa

fathy
. Electromagnetic Field, PHY
321

20

7
-

Magnetization in Materials

>

0

paramagnet

<

0
Diamagnetic

:
permeability of the

Material (
henrys/meter)

r

: relative
permeability of

the material