MAGNETIC DOMAIN,
MAGNETIC FIELD AND
MAGNETIC LINES OF
FORCE
MAGNETIC DOMAINS
Most
materials cannot be
magnetized. Iron and a few other
materials such as steel, nickel and
cobalt can be magnetized.These
materials have regions called
magnetic domains.
MAGNETIC DOMAINS
Magnetic
domains, which are
clusters of many atoms, can be
thought of as tiny magnets.
Substances that can be
magnetized can be thought of
as consisting of many tiny
magnets.
How does the arrangement of the
“tiny magnets” differ between the
unmagnetized and magnetized
substances?
LOOK AT THIS!
BEFORE: When the material is unmagnetized,
the domains are not lined up in a definite way.
They are randomly arranged.
LOOK AT THIS!
AFTER: When the material is magnetized,
the domains line up in a definite pattern.
All the north poles point in one direction,
and the south poles in the other.
LOOK AT THIS!
BEFORE:
AFTER:
CLASSIFICATION OF MATERIALS ACCORDING TO
THEIR ATTRACTION TO MAGNETS




FERROMAGNETIC - materials which are strongly
attracted to a magnet, example is alnico
PARAMAGNETIC – substances which are so weakly
attracted by a magnet that normal conditions even a
very strong magnet seems to have no effect on
them.
DIAMAGNETIC – materials that were repelled by
magnets although they themselves were not
magnets. They were discovered by Michael Faraday.
FERRIMAGNETIC – they are strongly magnetic but good
electrical insulators.
SUBSTANCE OR MATERIALS
ATTRACTED TO A MAGNET
REPELLED BY A MAGNET
FERROMAGNETIC
DIAMAGNETIC
Strongly attracted
e.g. Iron
Nickel
Cobalt
Heusler’s alloys
PARAMAGNETIC
Very Weakly Attracted
e.g. Platinum
Aluminum
Manganese
Liquid Oxygen
FERRIMAGNETIC
Strongly Attracted but
Electrical Insulators
e.g. Ferrites
Ceramics
e.g. Glass
Copper
Silver
Gold
Antimony
Mercury
Water
Bismuth
SHAPE OF MAGNETS
Disc
Horse-shoe magnet
Rod
Cylindrical
Block
Ring
Bar
U-shape
Shapes of Magnets
U-shape
Horse-shoe
Block
Disc
Ring
Bar
Cylindrical
WHAT IS MAGNETIC
FIELD ?
FROM THE PAST LESSONS....
What is gravitational field?
 What is magnetic field?
 What is magnetic domains?
 What are the classification of materials
according to their attraction to magnets?

MAGNETIC FIELDS
A
magnetic field is the region in
space around a magnet in which its
force affects another magnet or other
magnetizable objects.

Magnet has the ability to attract or exert
force on objects at a distance through
its field.
MAGNETIC FIELDS
A
good picture of a magnetic field
can be made by sprinkling iron
filings around a magnet.
EXAMPLE
OF
MAGNETIC FIELD
North Geographic Pole
`
Approximate location:
72°N, 97°W
North
Magnetic Pole
1,800 miles ,
Northwest of the
South Geographic
Pole
South Magnetic
Pole
Located at
McClintock Sound, north
of Hudson Bay
Approximate Location;
68°S, 148°E
South Geographic Pole
EVERY MAGNET HAS ITS OWN MAGNETIC
FIELD.

Figure A:
Figure B:
1. Trace the path of the iron filings in each figure.
2. What do you observe?___________________________
3. In which part do field tracer grains cling most?
4. In which part do they appear dispersed?
5. Is magnetic lines of force confined in only one place? Why
or why not?
 The
magnetic field changes the filings
into little magnets that attract one
another. This makes the filings form
long and thin chains. The chains line
up in the shape of the magnetic field.
Fig. A: Bar Magnet
Figure A shows the magnetic field around a bar
magnet. The arrowheads show the direction of the
magnetic lines of force, which come out of the N
pole and enter the S pole. The concentration of lines
of force at the poles shows that the field is strongest
there.
Figure B shows the magnetic field around a Ushaped magnet. The shape crowds the lines of force
together in between the two poles. This means that
the magnetic force between the poles becomes very
strong. This is also the reason why a horseshoe
magnet can lift greater weights than a bar magnet.
Fig. B: U-shaped magnet
FIG. C: MAGNETIC LINES OF FORCE (A) BETWEEN TWO UNLIKE POLES
(B) BETWEEN LIKE POLES
(a)
(b)
In studying magnets in 1820s, Michael Faraday described
magnetic fields through magnetic lines of force (Fig. C)
Magnetic lines of force never overlap even when the poles of
the two magnets are brought close to one another.
At
what point around the magnets
are the magnetic field lines closer
together or the margaha cling
most?
 More
lines of induction are found at
the poles than at points farthest
away.
MAGNETIC FLUX Ф
The greater the flux perpendicular unit area, the
stronger the magnetic field. Around a magnet, the
strength and direction of the magnetic field vary. At
any point around a magnet, the field has a magnitude
or strength which depends on the magnetic flux per
unit area Ф/A. The direction is shown by the North
pole of the compass needle. Hence, the magnetic field
is a vector quantity. It is represented by B. In symbols,
the magnetic field at a point is expressed as:
B= Ф/A.
The unit of flux is the weber and that of the field is
the tesla. From the above equation, we can say that
1 tesla = 1 weber/m2.
MAGNETIC FLUX
The number of lines passing through a
perpendicular area reflects the strength of the
magnetic field at that portion.
 The number of group lines passing through a
unit area is called magnetic flux (Φ).
 Weber is the unit of magnetic flux.
 Tesla – unit of magnetic field

ACTIVITY NO.3
Electricity and Magnetism
I. ARRANGE THE JUMBLED LETTERS TO FORM THE WORD(S), THAT BEST FITS
THE STATEMENT.










1. Natural magnets - COILAN
2. Clusters of many atoms that act as tiny magnets in a material
MAINODS
3. A region around a magnet - SFILEDGENAMICT
4. Imaginary lines that represent magnetic field
SLIENSOFGENTAMICFOECR
5. Materials that are strongly attracted to magnet - GENTAMICORREF
6. Materials that are repelled by magnet - GENTAMICIAD
7. Materials that are slightly attracted by magnet - GENTAMICARAP
8. A substance that possesses magnetic properties - NETGAM
9. Iron and other elements can become strongly magnetized
NETGAMITAZIONT
10. A magnet has two - SLOPE
II. COMPLETE EACH STATEMENT BY SUPPLYING THE CORRECT
TERM OR PHRASE.










1. The N pole of a magnet will be attracted to the _____ pole of another
magnet.
2. Alloys and ceramics are used to make _______magnets.
3. The S pole of the earth’s magnetic field is located in ________.
4. Many magnetic lines of force go into a magnet at its ________.
5. A suspended solenoid will rotate until it is lined up with the earth’s
______.
6. Regions containing groups of atoms that act like small magnets are
called________.
7. The relationship and interaction between electricity and magnetism is
called___________.
8. Like poles of magnets ________each other.
9. ______ are objects that attract material containing iron and they always
face the same direction when moving freely.
10. Natural magnets are made of iron ore called ________.
III. ANSWER THE FOLLOWING
It is a giant magnet
2. In what part of the magnet do lines of force
concentrate?
3. It is the number of group lines passing through
a unit area.
4. What is the unit of magnetic field?
5. What is the unit of magnetic flux?
6-10 Give uses of magnets
1.
. CHOOSE THE LETTER(S) OF THE BEST ANSWER
1. The N pole of a compass needle points to the south magnetic pole of the earth
because that pole is
a. an S pole b. an N pole c. a large iron deposit d.near the north geographic pole
2. If the poles of two magnets repel each other
a. both poles must be S poles.
c. one pole is an S and the other is an N.
b. both poles must be N poles.
d. both poles are of the same kind.
3. Magnetizing a piece of iron is a process by which
 a. magnetic atoms are added to the iron.
c. existing atomic magnets are
brought into line.
 b. magnetic lines of force are brought into line. d. each atom in the iron is
converted into a magnet.
4. A magnetic field can make a compass needle turn because the field
 a. attracts N poles.
c. comes from the center of the earth.
 b. is produced by a magnet.
d. exerts forces on the atomic currents in the
compass needle
5.The iron atom acts as a magnet because
c. the electrons have
negative charge.
 b. the electrons have a spinning motion.
d. the neutrons have no charge.
6. A steel sewing needle can be made into a magnet by
 a. banging it on a table.
c. placing it near a compass.
 b. soaking it in mercury.
d. stroking it with a magnet in one direction only.
7. If a magnet is brought near a magnet suspended on a string, the
 a. N poles attract each other.
c. S poles attract each other.
 b. N poles attract the S poles.
d. N poles repel the S poles.
8. The lines of force of unlike poles placed near each other
 a. curve away from each other.
c. cancel each other.
 b. connect the poles.
d. none of these.

a. it has an equal number of protons and electrons.
9. A device that turns electric energy into sound energy is
 a. a speaker b. a generator c. a VCD player
d. a transformer
10. A piece of copper cannot be made into a magnet because
 a. copper cannot be charged.
 b. the domains are already aligned.
 c. the copper atoms have no charge.
 d. electrons spinning in opposite directions in copper cancel
each other.
ANSWER KEY
I
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
Alnico
Domains
Magnetic fields
Magnetic lines of force
Ferromagnetic
Diamagnetic
Paramagnetic
Magnet
Magnetization
Poles
II
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
South
Permanent
North geographic pole/ North pole
Pole
Magnetic field
Domains
Electromagnetism
Repel
Ferromagnetic
Lodestone/ Magnetite
III
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
Earth
Poles
Magnetic flux
Tesla
Weber
Compass
Speaker
Motors, computers memory, decorative materials
Generators
Electric fan
IV. MULTIPLE CHOICE
1.D
2. A, B, D
3. C
4. D
5. B
6. D
7. B
8. B
9. A
10. D
ASSIGNMENT






How does electricity and magnetism related to each
other?
What is an Electromagnet?
What is/are common between a permanent magnet and
an electromagnet?
How are electromagnets different from the permanent
magnets?
Factors affecting the magnetic field strength
Electromagnets at work
PHYSICS,SEMP
pp. 194-202