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

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

DIAMAGNETIC

e.g. Glass Copper Silver Gold Antimony Mercury Water Bismuth

Disc

SHAPE OF MAGNETS

Horse-shoe magnet

RodCylindrical

Block

Ring

BarU-shape

Shapes of Magnets

U-shapeHorse-shoe BlockDiscRingBarCylindrical

Magnets

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

South Magnetic Pole

Located at McClintock Sound, north of Hudson Bay

Approximate location:72°N, 97°W

South Geographic Pole

North Magnetic Pole

1,800 miles , Northwest of the

South Geographic Pole

Approximate Location;

68°S, 148°E

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.

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.

Fig. A: Bar Magnet

Fig. B: U-shaped magnet

Figure B shows the magnetic field around a U-shaped 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. C: MAGNETIC LINES OF FORCE (A) BETWEEN TWO UNLIKE POLES

(B) BETWEEN LIKE POLES

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.

(a) (b)

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 ФThe 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

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

ACTIVITY NO.3Electricity and Magnetism

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 ________.

1. It is a giant magnet2. 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

III. ANSWER THE FOLLOWING

. 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 isa. 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 othera. 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 a. it has an equal number of protons and electrons. 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.

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 KEYI

1. Alnico2. Domains3. Magnetic fields4. Magnetic lines of force5. Ferromagnetic6. Diamagnetic7. Paramagnetic8. Magnet9. Magnetization10. Poles

II

1. South2. Permanent3. North geographic pole/ North pole4. Pole5. Magnetic field6. Domains7. Electromagnetism8. Repel9. Ferromagnetic10. Lodestone/ Magnetite

III

1. Earth2. Poles3. Magnetic flux4. Tesla5. Weber6. Compass7. Speaker8. Motors, computers memory, decorative materials9. Generators10. Electric fan

IV. MULTIPLE CHOICE

1.D2. A, B, D3. C4. D5. B6. D7. B8. B9. A10. 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