Bellwork: Monday 5/21/20121. What causes a

compass to behave as it does?• Earth’s gravity• Earth’s shape• Earth’s geographic

north pole• Earth’s magnetic field

2. Magnetic poles that are alike• attract each other• repel each other• do not interact• have the same shape

3. As in the case of unlike magnetic poles, unlike electric charges• attract each other• repel each other• exist in pairs• do not interact

1. Earth’s magnetic field…causes a compass to behave as it does

2. Magnetic poles that are alike…repel each other

3. Unlike electric charges...attract each other

Packet 16, Pg 1- History of Magnetism• 2000+ years ago

– Greeks near the city of Magnesia found strange and rare stones with the power to attract iron—called them magnetite (Fe3O4)

– Lodestone- naturally magnetized piece of magnetite

• 1000 years ago– Chinese stroked a steel needle

with “lodestone” (‘lode’ means to lead or to attract) and it became "magnetic" as well.

– When freely suspended, it pointed north-south. The magnetic compass soon spread to Europe. 

Christopher Columbus- 1492

• Used a compass when he crossed the Atlantic ocean

• His observations:– the compass

needle strayed slightly from exact north• as indicated by the

stars– the variation

changed during the voyage

What’s happening?Basically, people knew the

magnetism existed, and learned useful applications

for it. But, they did not understand

how it worked!

500 years ago• William Gilbert, physician

to Queen Elizabeth I of England, proposed an explanation: – “The Earth itself is a giant

magnet, with its magnetic poles some distance away from its geographic poles”

• Geographic poles- the points defining the axis around which the Earth turns

Safety with Magnets • Magnets should not be held

near these things:– Credit cards– Magnetic I.D. cards – TV or VCR – Computer monitor– Floppy computer discs– Cassette Tapes/ Video Tapes– Tape Recorders– Radio– Any Speakers

– A magnet will harm most electrical devices!!!

Using Magnetism for Evil?!

• Magneto is a powerful mutant with the ability to generate and control electromagnetic forces.

• He can shape and manipulate magnetic fields that exist naturally or artificially.

• Magneto has been the X-Men's most prominent enemy ever since his first appearance.

Magnetic Force• 4.5- TSW DESCRIBE THE FOLLOWING FORCE:

MAGNETISM.• 6.14- TSW DEMONSTRATE THE PROPERTIES

THAT CAN BE USED TO IDENTIFY MATTER: MAGNETISM.

• Magnetism- physical property of a substance; the force of attraction or repulsion of magnetic materials– Force is stronger than gravitational force

(allows us to pick up objects using a magnet )

• Magnetic fields:– Can be mapped– More field lines indicates the strength of

the magnet in that area– Strongest near the poles  – Stronger closer to the magnet than further

away.– 7.20- TSW DEMONSTRATE THAT THE

STRENGTH OF THE MAGNETIC FORCE DEPENDS ON THE DISTANCE BETWEEN THE MAGNET AND OBJECTS.

Properties of Magnets

• All magnets have two opposite poles.

• No matter how small or broken, each piece will have its own positive and negative pole. 

• There are no unpaired poles.  Poles have been labeled as north and south.

• A magnet is capable of producing an electric current.

• When poles get near each other, they exert magnetic forces on each other– Magnetic poles that are alike

repel each other.– Magnetic poles that are

different attract each other.

S N

S N

S N S N

Magnetism• Paramagnetism - When a

paramagnetic material is placed near a magnet, it will be attracted to the region of greater magnetic field– Exhibited by: materials containing transition

elements, rare earth elements and actinide elements 

• Diamagnetism - When a diamagnetic material is placed near a magnet, it will be repelled from the region of greater magnetic field– Exhibited by: all common materials, but is very

weak• Ex. People, frogs• Ex. Metals such as bismuth, copper, gold, silver and lead,

as well as many nonmetals such as water

"Magnetic Man"• Malaysia, Liew Thow Lin, 70

years old• Has the ability to make

metal objects stick to his skin.

• After reading an article about a family in Taiwan who possessed such power, he says he took several iron objects and put them on his abdomen, and to his surprise, all the objects including an iron, stuck on his skin and didn't fall down.

• Pulled a car 20m along a level surface by means of an iron chain hooked to an iron plate on his midriff

• Since this "gift'' is also present in three of his sons and two grandchildren, he figures it's hereditary.

The boy with the magnetic personality

• May 11, 2011• Six-year-old Croatian, Ivan Stoiljkovic, can stick

metal objects to his body such as: spoons, mobile phones and even frying pans

• Reality: Doctors say he's ability is related to suction properties in his skin and not to magnetic force but anyway what he can do is very impressive.

3 Types of Magnets1. Natural (Permanent) Magnet- A magnet that retains its

magnetization after removal from a magnetic field. • Can occur naturally. • Lodestone is a natural permanent magnet.• Can produce forces at all times • Earth produces a magnetic field due to molten iron in

core and spinning of the earth• Permanent magnets can be damaged from extreme heat

and dropping

Permanent MagnetsEach atom in a ferromagnetic material like iron is like a little magnet.

These magnets are all aligned in tiny regions called “domains”.

At high temps these “domains” can align in the presence of an external field (like Earth’s) leaving a permanent magnet.

Domains

Lets melt the iron, and bring in a magnetic field.

Now, when we let the solid cool down, and take away the external magnetic field, we have formed a permanent magnet in the same direction as external field.

Temp

Melting point

Bar Magnet

3 types of magnets2. Temporary Magnet- only have

magnetic properties for a short period of time, after exposure to a permanent magnet

• Iron—composed of molecules (domains)

– All different directions = no magnetic force or pull

– All lined up in one direction = force to pull things towards them

Groups of atoms join so that their magnetic fields are all going in the same direction

These areas of atoms are called “domains”• An unmagnetized

substance looks like:

• While a magnetized substance looks like:

How to demagnetize a magnet:

1. Impact (hit it)2. Heat it

This causes the domains to become random again!

3. Electricity

3 types of Magnets3. Electromagnet- temporary magnet, made by

coiling wire around a piece of soft iron. – 7.18- TSW PROVIDE EVIDENCE THAT ELECTRIC CURRENTS

CAN PRODUCE MAGNETIC FORCES.– 7.19- TSW PROVIDE EVIDENCE THAT MAGNETS CAN

CAUSE ELECTRIC CURRENTS.– When an electric current is passed through the wire,

a magnetic field is produced. – The field magnetizes the iron core by aligning

domains within the iron.

Bellwork: Tuesday 5/22/20121. What happens if a magnet breaks

in half?– One half has a north pole only, and one

half has a south pole only– Neither half will have a pole– Each half will be a new magnet, with

both a north and south pole– Neither half will attract or repel.

2. Draw arrows to show if the cars attract or repel each other. On the space to the right, write the word that describes the action of the cars (attract or repel).

3. The region around a magnet where the magnetic force is exerted is known as its– magnetic pole– magnetic field– magnetic domain

4. Magnetism can be considered a– nuclear property– physical property– chemical property

5. A temporary magnet– keeps its magnetism for a long time– cannot be destroyed– easily loses its magnetism

• Attract

• Attract

• Repel

S N S N S N

What on Earth is a Cow Magnet?• Magnets come in many

shapes and sizes, but the cow magnet was invented to solve a very serious problem of dairy farmers.

• When the cow grazes, it often consumes and swallows small pieces of iron: baling and barbed wire, staples, nails, and other metallic objects.

• These objects are indigestible and lodge in the reticulum and cause inflammation.

• This results in lower milk production (for dairy cattle) or lower weight gain (for feeder stock).

• This condition is called hardware disease.

• Solution: A rancher/ farmer feeds a magnet to each calf at branding time; the magnet settles in the rumen or reticulum and remains there for the life of the animal.

• The cow magnet attracts such objects and prevents them from becoming lodged in the animal's tissue. While the resultant mass of iron remains in the cow's rumen as a sort of bezoar, it does not cause the severe problems of hardware disease.

• One small cow magnet can help a cow for her whole life!

Magnetic Fields- pg. 3Procedure:

1. Place a magnet into a tray, put a piece of paper over the magnet.

2. Lightly sprinkle iron filings on and around the magnet, gently tap the paper.

3. Observe the formation around the magnets, and sketch what you see.

Types of Demonstration:1. One magnet2. Two magnets- Attracting3. Two magnets- Repelling

Mapping Magnetic Fields• One Magnet

• Two Magnets- Attracting

• Two Magnets- Repelling

N S N S

N S S N

N S

MAGNETIC FIELDS- One Magnet• This picture demonstrates what occurs

when one magnet is placed on paper, and iron filings are sprinkled around it.

MAGNETIC FIELDS- Two Magnets Attracting

• This picture has two magnets placed on a piece of paper with their opposite poles facing each other, and iron filings are sprinkled around them.

MAGNETIC FIELDS- Two Magnets Repelling

• Pictured here are two magnets placed on a piece of paper with their like poles facing each other, and iron filings are sprinkled around them.

Like poles repel…

Opposite poles attract!

The Earth’s magnetic field extends far into space. It is called the “magnetosphere.”

When the magnetic particles from the sun, called “solar wind”, strike this magnetosphere, we see a phenomenon called…

The Aurora Borealis in the Northern HemisphereAnd the Aurora Australis in the Southern Hemisphere

• Magic of Magnets - 15 minutes

Tuesday 5/22/12

Bellwork: Wednesday 5/23/20121. True / False. You can see

magnetic fields without assistance.

2. By looking at magnetic field patterns, you can tell where the magnetic forces are the strongest. Where are you looking and what do you see?

3. You can tell by these lines whether the magnets are (A) attracting, or (B) repelling. What would each look like??—sketch and describe.

1. False. Magnetic fields are invisible (until you use iron filings to help map them!).

2. Magnetic force is strongest at the poles.– Where all of the lines

converge/intersect– Where the lines are most

concentrated

3.(A) Attracting- lots of lines connecting between them(B) Repelling- lines do not interact or touch—nothing observed between the magnets

Electricity/Magnetism Videos• How Electricity is Created from Magnets

– 9.15- Start 3.50 end 6.18• Electricity_and_Magnetism__Current_Elect

ricity 16.58– Start .36 end 7.29

Energy Unit Test Corrections• You only need ONE sheet

– Use an extra sheet of paper for more corrections

• Rest of class– Plenty of time so EVERYBODY will be turning

in test corrections.– If you don’t turn them in – you will LOSE

points!• Weren’t actually two versions so…you

can work with anybody!• To do more test corrections, get on to the

website at the top of the page to access the test.

• Understanding Magnetism Video 50 minutes– Complete ½ page quiz

as you watch on pg. 3 in Packet 15

Wednesday 5/23/12