1. Electricity and Magnetism
Chapter 1: Magnetism
Section 1: What is Magnetism

2. Vocabulary Magnet Magnetic pole Magnetic force Magnetic field
Magnetic field lines

3. Properties of Magnets
A magnet is any material that attracts iron and materials that contain iron
More than 2,000 years ago, people living in the ancient Greek city of Magnesia (now in Turkey) discovered an odd kind of rock.
This rock contained a mineral called magnetite.
Both the name magnet and the mineral named after the city these were found in
Rocks containing magnetite attracted or repelled other magnetic rocks.
The attraction or repulsion of magnetic materials is called magnetism.

4. About a 1,000 years later, people discovered if they allowed a magnetic rock to swing freely, it would always point in the same direction.
That direction was always towards the North Star, Polaris.
This star was also called the leading star, or lodestar.
Because of this, magnetic rocks are also known as lodestones.

5. Magnets have the same properties as magnetic rocks
They attract iron and materials that contain iron.
Magnets attract or repel other magnets
One part of a magnet will always point north when allowed to swing freely

6. Magnetic Poles Any magnet, no matter its shape, has two ends.
Each end of the magnet is called a magnetic pole
The magnetic effect is strongest at the magnetic pole.
Most magnets have the pole of the magnet that points north labeled as north.
Thus, a magnet will always have a north pole, and a south pole.
Magnetic poles that are unlike attract each other
Magnetic poles that are alike repel each other.
So the end of the magnet that points north, is it like or unlike the magnetic end of our earth?

7. Magnetic Force
The attraction or repulsion between magnetic poles is a push or a pull
Therefore, it’s a force.
This attraction or repulsion between magnetic poles is magnetic force.
Any object that can exert a magnetic force is considered to be a magnet.

8. Magnetic Fields Not where we find iron bunnies
The magnetic force is strongest at the pole, but not limited to the poles.
Magnetic forces are exerted all around a magnet.
The area of magnetic force around a magnet is called its magnetic field.
Because of magnetic fields, magnets can interact without touching.

9. Magnetic field lines are invisible lines that map out the magnetic field of a magnet.
They spread out from one pole, curve around the magnet and return to the other pole.
Lines form complete loops from pole to pole and never cross.
Arrows are used to indicate the direction of magnetic field lines
Always leave the north pole and enter the south pole
The distance between the field lines tells the strength of the magnetic field
Closer lines means strong field

11. Single Magnetic Field Like the picture we just saw
Photograph shows iron filings sprinkled around a magnet
The magnetic forces of the magnet act on the iron filings and align them along the field lines

12. Combined Magnetic Fields
When two or more magnetic fields overlap, the results are combined.

13. Electricity and Magnetism
Chapter 1: Magnetism
Section 2: Inside a Magnet

14. Vocabulary Magnetic domain Ferromagnetic material Temporary magnet
Permanent magnet

15. Overview
Section focuses on what makes some objects magnetic while others are not.

16. The Atom
The magnetic properties of a material depend on the structure of its atoms.
Remember
Every atom has a center region called a nucleus
Made up of positively charged protons and neutrally charged neutrons
Outer region of an atom is mostly empty space
However, negatively charged electrons exist outside of the nucleus.
It is the electrons in an atom that are responsible for its magnetic properties

17. Electron Spin Not a crazy new dance craze
Each electron in an atom has a property called electron spin
This means each electron behaves as if it were spinning
A spinning electron produces a magnetic field that makes the electron behave like a tiny magnet in the atoms.
In most atoms, electrons form pairs that spin in opposite directions.
Opposite spins produce opposite magnetic fields that cancel
Therefore, most atoms have weak magnetic properties
However, some atoms contain electrons that are NOT paired.
These atoms tend to have strong magnetic properties.

18. Magnetic Domains
The magnetic fields of the atoms in most materials point in random directions.
This results in magnetic fields canceling themselves out almost entirely.
So the magnetic force would be so weak we usually can’t detect it.
However, in certain materials, the magnetic fields of many atoms are aligned with one another.
A grouping of atoms that has their magnetic fields aligned is known as a magnetic domain.
The entire domain acts like a bar magnet with a north pole and a south pole.

19. Alignment of Domains
The direction in which the domains point determines if the material itself is magnetized or not.
In a material that is not magnetized, the magnetic domains point in random directions.
Therefore, the magnetic fields of some domains cancel the magnetic field of other domains.

20. In a magnetized object, the magnetic domains are generally pointing in the same direction.
In other words, the magnetic fields are aligned.

21. Magnetic Materials
A material can be a strong magnet if its magnetic domains align.
A material that shows strong magnetic properties is said to be a ferromagnetic material.
The word ferromagnetic comes from the Latin ferrum, which means “iron.”
So a ferromagnetic material behaves like a piece of iron when it is placed in a magnetic field.
In nature, iron, nickel, cobalt and gadolinium are common ferromagnetic materials.
Others include the rare elements samarium and neodymium, which can be made into extremely strong magnets.

22. Some magnets are made from several different metals.
Called an alloy
For example, the magnetic alloy alnico is made from aluminum, nickel, iron, and cobalt.
Powerful magnets are also made from allows of platinum and cobalt, and alloys of cobalt and neodymium
Today, the most common magnets are not made from alloys, but from a material called ferrite.
Ferrite is a mixture of substances that contain ferromagnetic elements.
It is brittle and chips easily, but tends to be stronger and less expensive than metal magnets of similar size.

23. Making and Changing Magnets
A magnet can be made from ferromagnetic material, however, no magnet lasts forever.
Magnets can be made, destroyed, or broken apart.

24. Making Magnets
A magnet can be made by placing an unmagnetized ferromagnetic material into a strong magnetic field or by rubbing the material with one pole of a magnet.
Suppose I want to magnetize a paper clip
Made of steel, and steel contains iron.
If I rub the clip in one direction with one pole of a magnet, the magnetic field of the magnet causes the domains in the paperclip to line up in the same direction as the magnet.
The more domains that line up, the more magnetized the paper clip becomes.

25. Temporary vs. Permanent Magnets
Some materials, such as steel or pure iron, are easy to magnetize, but lose their magnetism quickly.
A magnet made from a material that easily loses its magnetism is called a temporary magnet.
Other materials, such as those in strong magnets, are hard to magnetize, but tend to stay magnetized.
A magnet made from a material that keeps its magnetism for a long time is called a permanent magnet.

26. Destroying Magnets
Like a temporary magnet, a permanent magnet can also become unmagnetized.
One way to do so is to drop it, or strike it hard
If hit hard, the domains can be knocked out of alignment
Another way is to heat it
When heated, the particles in the object vibrate faster and more randomly.
This makes it difficult for all of the domains to stay lined up.
Above a certain a temperature, every ferromagnetic material loses its magnetic properties
This temperature varies from material to material

27. Breaking Magnets
If I break a magnet, I just get two smaller magnets, each with a north and south pole.
The magnet will have mostly aligned domains
When you break the magnet, that doesn’t change the alignment of the domains
So each piece will still have aligned domains, each in the same direction.

29. Electricity and Magnetism
Chapter 1: Magnetism
Section 3: Magnetic Earth

30. Vocabulary Magnetic declination Van Allen belts Solar wind
Magnetosphere
Aurora

31. Earth as a Magnet
In the late 1500’s, an English doctor Sir William Gilbert became interested in compasses.
He confirmed that a compass will always point in the same direction, no matter where it is.
Navigators knew this at the time
However, nobody knew why this occurred.
Gilbert hypothesized the compass behaves as it does because the Earth acts like a giant magnet.
He was laughed at for this idea
But he turned out to be correct
Just like a bar magnet, Earth has a magnetic field surrounding it, and two magnetic poles.

32. Earth’s Core
Gilbert thought the Earth’s core, contained magnetic rock.
Currently, we think this is not the case
Core too hot to be solid, so too hot to be magnetic.
The “how” of Earth’s magnetism is not completely understood
However, we do know that the circulation of molten material in Earth’s core is related to Earth’s magnetism.

33. Earth’s Magnetic Poles
We know the Earth rotates on its axis, around the geographic poles.
Earth also has magnetic poles.
The magnetic poles are not in the same place as the geographic poles.
For example, the magnetic pole in the Northern Hemisphere is located in northern Canada, and is about 1,250 km (about 800 miles) from the geographic north pole.

35. Magnetic Declination
If you use a compass, you have to account for the fact that Earth’s geographic and magnetic poles are different.
The magnetic declination is the angle between the geographic north and the north to which a compass needle points.
The magnetic declination changes as the location of the magnetic poles change.

36. Earth’s Magnetic Field
Since Earth produces a strong magnetic field, Earth itself can make magnets out of ferromagnetic materials.
Earth as a magnet maker
Suppose you have an iron bar lying in a north-south direction for many years.
Earth’s magnetic field may attract the domains strongly enough for them to line up in the same direction.
When the domains align, it is a magnet.
This can happen to everyday objects
Filing cabinets CAN become magnets just by sitting around.

37. Earth Leaves a Record
Earth’s magnetic field also acts on rocks that contain magnetic materials, such as rock on the ocean floor.
Rock is produced on the ocean floor from molten material that seeps up from the mantle.
When the rock is molten, the iron it contains lines up in the direction of the Earth’s magnetic field.
As it cools and hardens, the iron is locked into place.
This creates a permanent record of the magnetic field.
As scientists studied these rocks, they discovered that the direction and strength of Earth’s magnetic field has changed over time.
It seems to reverse every million years or so.

38. Rocks farther from the mid-ocean ridge are older than the ones closer.
The different colored layers indicate the direction of the Earth’s magnetic field over time.
Rocks farther from the mid-ocean ridge are older than the ones closer.
Why does it change direction?
We don’t know.

39. The Magnetosphere Earth’s magnetic field extends into space.
Space is not empty; it contains electrically charged particles.
So, Earth’s magnetic field affects the movements of electrically charged particles in space.
These charged particles also affect Earth’s magnetic field.

40. Van Allen Belts
Between 1,000 and 25,000 km above Earth’s surface are two doughnut-shaped regions called the Van Allen Belts.
These regions contain electrons and protons traveling at very high speeds.
We must shield spacecraft and satellites so they will not be affected.

41. Solar Wind
Other electrically charged particles in space come from the Sun.
Earth and other objects in our system experience a solar wind.
The solar wind is a stream of electrically charged particles flowing at high speed from the Sun.
It pushes against the Earth’s magnetic field and surrounds the field.
The region of Earth’s magnetic field shaped by the solar wind is called the magnetosphere.
The solar wind constantly reshapes the magnetosphere as Earth rotates on its axis.

43. Auroras
Although most particles in the solar wind cannot penetrate Earth’s magnetic field, some particles do.
They follow Earth’s magnetic field lines to the magnetic poles.
Since at the poles, the magnetic field lines dip down to Earth’s surface.

44. The result is a glowing curtain of bright light in the sky.
When high-speed, charged particles get close to Earth’s surface, they interact with atoms in the atmosphere.
The result is a glowing curtain of bright light in the sky.
This is called an aurora.