SIMPLE PHENOMENA OF MAGNETISM

a) PROPERTIES OF MAGNET

1. MAGNETIC POLES

- placed on the edge of the bar magnet

- the magnetic effect are strongest HERE

2. NORTH and SOUTH POLE

- the end of the bar magnet that points to the Northern end of the EARTH is NORTH pole (or N pole)

- the end of the bar magnet that points to the Southern end of the EARTH is SOUTH pole (or S pole)

3. LAW OF MAGNETIC POLE

SAME pole REPEL, DIFFERENT pole ATTRACT

b) DIFFERENCE BETWEEN FERROUS AND NON FERROUS MATERIALS

FERROUS MATERIAL ASPECT NON – FERROUS MATERIAL

YESRESPOND TO THE MAGNETIC FIELD NO

HIGHPERCENTAGE OF

IRON’S ATOMS VERY LOW OR NONE

YES HARDNESS DEPEND ON MATERIAL

YES BRITTLE DEPEND ON MATERIAL

YESMETALLIC ELEMENT DEPEND ON MATERIAL

IRON, COBALT, NICKEL EXAMPLE BRASS, COPPER, WOOD, PLASTIC

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SOME FERROUS METALS AND PROPERTIES

  

NAME ALLOY OF PROPERTIES USESMild Steel Carbon 0.1 - 0.3%

Iron 99.9 - 99.7%Tough. High tensile strength. Can be case hardened. Rusts very easily.

Most common metal used in school workshops. Used in general metal products and engineering.

Carbon Steel Carbon 0.6 - 1.4%Iron 99.4 - 98.6%

Tough. Can be hardened and tempered. Cutting tools such as drills.

Stainless steel Iron, nickel and chromium.

Tough, resistant to rust and stains. Cutlery, medical instruments.

Cast iron Carbon 2 - 6%Iron 98 - 94%

Strong but brittle. Compressive strength very high.

Castings, manhole covers, engines.

Wrought iron Almost 100% iron Fibrous, tough, ductile, resistant to rusting.

Ornamental gates and railings. Not in much use today.

SOME NON - FERROUS  METALS AND PROPERTIES

NAME COLOUR ALLOY OF; PROPERTIES USESAluminium Light grey Aluminium 95%

Copper 4%Manganese 1%

Ductile, soft, malleable, machines well. Very light.

Window frames, aircraft, kitchen ware.

Copper Reddish brown Not an alloy Ductile, can be beaten into shape. Conducts electricity and heat.

Electrical wiring, tubing, kettles, bowls, pipes.

Brass Yellow Mixture of copper and zinc 65% - 35% most common ratio.

Hard. Casts and machines well. Surface tarnishes. Conducts electricity.

Parts for electrical fittings, ornaments.

Silver Whitish grey Mainly silver but alloyed with copper to give sterling silver.

Ductile, Malleable, solders, resists corrosion.

Jewellery, solder, ornaments.

Lead Bluish grey Not an alloy. Soft, heavy, ductile, loses its shape under pressure.

Solders, pipes, batter

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HOW TO IDENTIFY A MAGNET?

Let say we have an object A and move it towards the N pole of a suspended bar magnet, observe what is going to be happened. If

a) REPULSION occurs, object A is a magnet

HOWEVER, if

b) ATTRACION occurs, object A can be either a ferrous material (e.g: iron, cobalt, nickel) or a magnet itself with the opposite pole which is S pole

MAGNETIC INDUCTION

Definition:

Process of inducing (bringing about) the magnetism in ferrous material

How it going to be happen?

1st situation:

Take a few of safety pins or paper clips near to the permanent magnet; observe what is going to be happened.

Safety pins or paper clips will attracted to the permanent magnet, and become INDUCED MAGNET

2nd situation:

Move permanent magnet to the iron nail; monitor what is going to be happened.

The iron nail become an INDUCED MAGNET (attracted towards a magnet)

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REPULSION is the ONLY TEST to CONFIRM the MAGNETISM of an object

S

N

S

N

MAGNETIZATION and DEMAGNETIZATION

a) MAGNETIC DOMAIN

Definition:

A REGION within a magnetic material which HAS UNIFORM MAGNETIZATION.

Concept:

Magnetic domain structure is responsible for the magnetic behavior of ferrous materials like iron, cobalt and nickel

The regions separating magnetic domains are called domain walls where the magnetization rotates coherently from the direction in one domain to that in the next domain.

Refer to FIGURE A, the magnetic domains point in RANDOM DIRECTION FOR UNMAGNETIZED IRON BAR

HOWEVER, refer to FIGURE B, when a permanent magnet is BROUGHT NEAR to unmagnetized iron bar, iron bar become INDUCED MAGNET. The magnetic domains inside it point in the SAME DIRECTION

Phenomena related to magnetic domains:

i- MAGNETIC SATURATION

- A magnet can be said MAGNETICALLT SATURATED when it reaches its maximum strength. This happens when all of magnetic domains inside it are pointing in the same direction

ii- DEMAGNETIZATION of MAGNET

- Remove magnetism effect from a magnet

- Can be done by HEATING and HAMMERING

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Figure A Figure B

Domain wall

iii- STORAGE of MAGNET using SORT IRON KEEPERS

- To maintain the magnetic strength of permanent magnet, it should be put in between 2 soft irons (or called as “soft iron keeper”)

- In this way, the poles of atomic magnet are in closed loops with no free poles to weaken the magnetic domains

Soft iron keeper

- HOWEVER, if we put permanent magnet side by side, its magnetic strength become weaker due to the free pole near to the end of magnet will repel one another.

- Over the time, magnetic domains will be altered, thus weakening the magnet

b) WAYS OF MAKING MAGNET

i. Stroking method

- An unmagnetized steel bar is stroked several times with the same pole of a permanent magnet from one end to the other in one direction

- The steel bar will become a permanent magnet due to magnetic induction

ii. Electrical method using DC electrical source (battery)

- An unmagnetized steel bar is placed inside a solenoid. A solenoid is cylindrical coil which consists of hundred turns of insulated copper wires

- When a large DC current from battery flows throughout the solenoid, the steel bar will become a permanent magnet due to magnetic induction from current inside insulated copper wire

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c) WAYS OF DEMAGNETIZING MAGNET

i. Heating

- By heating a magnet strongly with a Bunsen burner, the magnet will lose its magnetism rapidly.

- The atoms of the magnet vibrate vigorously when heated, causing the magnetic domains inside it lose their alignment

ii. Hammering

- By applying large external force to a magnet, the atomic arrangement inside the magnet will change, causing the magnetic domains inside it lose their alignment, thus weaken the magnet

iii. Electrical method using AC electrical source (wall socket’s electricity)

- The most effective method of demagnetization

- A magnet is placed inside a solenoid and AC current pass throughout of it. The magnet is then slowly withdrawn in the East West direction during the process

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MAGNETIC FIELDS

Definition:

A REGION where a MAGNETIC MATERIAL or OBJECT, placed within the influence of the field, EXPERIENCES A MAGNETIC FORCE.

Characteristics:

It is invisible (CAN’T BE SEEN BY NAKED EYES)

It can be seen by placing A BLANK WHITE PAPER ON TOP OF A BAR MAGNET AND SPRINKLE IRON POWDER ON IT.

Represented by magnetic field pattern or known as magnetic field lines

Magnetic field pattern (magnetic field lines) can be seen as in Figure A-1 below

Characteristics of magnetic field line:

Directed OUTWARD from N POLE to S POLE

Do not CROSS or INTERSECT ONE ANOTHER

The CLOSER the MAGNETIC FIELD LINE, the STRONGER the MAGNETIC FIELD & vice versa.

Magnetic field lines between magnets:

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TEMPORARY and PERMANENT MAGNETS

Magnetic Properties of Iron and Steel

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