III. Magnetism Part 1
Introduction to Magnetism, Magnetic Forces and Magnetic Fields
Introduction to Magnetism, Magnetic Forces and Magnetic Fields
I remember living in Northern Michigan, the Beauty of the Aurora Borealis or Northern Lights on clear could nights. The fact that this grand spectacle is shaped by the same force that operates in common refrigerator magnets and children's horseshoe magnets is amazing to me. Also amazing is the Human body has a measureable magnetic field operated by the same laws, a field that is detectable by sensitive magnetic field instruments for up to 10-15 feet in space!! PEMF devices create changing magnetic fields that are even more dynamic than static magnet's as we'll see.
Magnetism is at the very heart of PEMF therapy and this and the next few modules will finally get into the REAL Physics of PEMF.
Magnetism is at the very heart of PEMF therapy and this and the next few modules will finally get into the REAL Physics of PEMF.
III. Charges in Motion Part 2 - Magnetism and Magnetostatics
In the last video we put charges in motion with basic ideas of current , voltage and resistance, NOW in this module we are going to see how moving charges create Magnetic fields.
Stationary Charges produce electric fields that are constant in time; hence the term electrostatics. As we'll see steady currents produce magnetic fields that are constant in time; this is called magnetostatics.
But let us begin first by looking at some basic concepts of Magnetism.
Many of us were exposed to magnetism at a young age with Horseshoe magnets, bar magnets, refrigerator magnets, and many toys that use magnets.
In fact Magnets are ALL around us...
In the last video we put charges in motion with basic ideas of current , voltage and resistance, NOW in this module we are going to see how moving charges create Magnetic fields.
Stationary Charges produce electric fields that are constant in time; hence the term electrostatics. As we'll see steady currents produce magnetic fields that are constant in time; this is called magnetostatics.
But let us begin first by looking at some basic concepts of Magnetism.
Many of us were exposed to magnetism at a young age with Horseshoe magnets, bar magnets, refrigerator magnets, and many toys that use magnets.
In fact Magnets are ALL around us...
- Computer Hard Drive Magnets, Magnetic recording and data storage equipment: tape recorders, VCRs, hard disks
- Microphones, Headphones, Loudspeakers
- Motors (e.g. washing machines, drills, food mixers, vacuum cleaners, hand dryers)
- Generators (e.g. Wind turbines, Wave Power, Turbo Generators, etc)
- Industrial lifting magnets
- magnetic levitation, used in a maglev train
- Door Catches, and Magnetic locks
- Magnetic Suspension, Brakes, alternators and all over your car
- Jewelery and bracelets
- Toys, games and puzzles
- Electric bells and buzzers
- Scientific equipment such as mass spectrometers, Particle accelerators and more
Magnets are also used heavily in industry, Mining, Food processing, glass and plastic, industrial ceramics mainly to remove impurities.
In allopathic medicine, powerful magnets are used in MRIs, NMR and other diagnostic equipment and in alternative medicine, magnetic therapy products abound for actual treatment... there are a LOT of static magnetic products, pads, mattresses and braces for just about every joint.
In this module we will look at what magnets really are, why current loops with steady current (ie. electromagnets) and static magnets (like ceramic, iron or neodynium) create the same magnetic field, what the magnetic force is, and how the magnetic fields are produced and how they are calculated. This will set the stage solidly for PEMFS which are changing magnetic fields which we will fully understand in later modules. But before we can truly understand a changing magnetic field, we first need to understand what magnetism is... So with compass in hand, let's begin this exciting journey of the world of magnetism.
In allopathic medicine, powerful magnets are used in MRIs, NMR and other diagnostic equipment and in alternative medicine, magnetic therapy products abound for actual treatment... there are a LOT of static magnetic products, pads, mattresses and braces for just about every joint.
In this module we will look at what magnets really are, why current loops with steady current (ie. electromagnets) and static magnets (like ceramic, iron or neodynium) create the same magnetic field, what the magnetic force is, and how the magnetic fields are produced and how they are calculated. This will set the stage solidly for PEMFS which are changing magnetic fields which we will fully understand in later modules. But before we can truly understand a changing magnetic field, we first need to understand what magnetism is... So with compass in hand, let's begin this exciting journey of the world of magnetism.
The Early Greeks found natural rock magnets in the area of Greece called Magnesia. They Called this magnetic stone Lodestone. These are naturally magnetized pieces of the mineral magnetite (an iron oxide compound), could attract iron.
The oldest known reference to lodestone’s properties appeared in 600 BC, when the Greek philosopher Thales of Miletus noted iron’s attraction to it.
Our term magnet derives from Magnesia. Greek magnēs lithos (Lodestone).
The oldest known reference to lodestone’s properties appeared in 600 BC, when the Greek philosopher Thales of Miletus noted iron’s attraction to it.
Our term magnet derives from Magnesia. Greek magnēs lithos (Lodestone).
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Lodestone Used for Navigation from the 1200s.
In 1263 Pierre de Maricourt mapped out the magnetic field of a lodestone with a compass. He discovered that a magnet has two magnetic poles a North and a South.
Lodestone needles were placed on cork which was floated in a water dish. The needle always pointed in a North/South Direction which helped ships to navigate their way.
In 1263 Pierre de Maricourt mapped out the magnetic field of a lodestone with a compass. He discovered that a magnet has two magnetic poles a North and a South.
Lodestone needles were placed on cork which was floated in a water dish. The needle always pointed in a North/South Direction which helped ships to navigate their way.
The Englishman William Gilbert (1540-1603), who was Queen Elizabeth's physician, was the first to investigate the phenomenon of magnetism systematically using scientific methods.
He also discovered that Earth is itself a weak magnet that was able to cause compasses to align themselves along a North/South axis.
Let's now explore some basic ideas of magnetism that you perhaps have heard before...
He also discovered that Earth is itself a weak magnet that was able to cause compasses to align themselves along a North/South axis.
Let's now explore some basic ideas of magnetism that you perhaps have heard before...
The Poles of a Magnet
A magnet, when suspended from a string will align itself with one pole pointing North and one pole pointing South. The north-seeking pole is labelled N while the South seeking pole is labelled S.
This is essentially what a compass is.
A magnet, when suspended from a string will align itself with one pole pointing North and one pole pointing South. The north-seeking pole is labelled N while the South seeking pole is labelled S.
This is essentially what a compass is.
Unlike electric charge, which can be separated, the magnetic poles cannot be separated. When a magnet is broken each piece will be found to have a North and South Pole.
That is, if you break a magnet in half, each piece still behaves as a complete magnet. Break the pieces in half again, and you will have four complete magnets.
Even when your piece is one atom thick, there are still TWO POLES. This suggests that atoms themselves are magnets. More on this later.
That is, if you break a magnet in half, each piece still behaves as a complete magnet. Break the pieces in half again, and you will have four complete magnets.
Even when your piece is one atom thick, there are still TWO POLES. This suggests that atoms themselves are magnets. More on this later.
Since a magnet's North pole is attracted to the Earth's Magnetic North Pole, the Magnetic North Pole must actually be a South pole, since only opposite poles attract each other. Likewise, the Magnetic South Pole must actually be a North Pole.
Also of Note is that the Earth's Geographic and Magnetic Poles differ by roughly 11 degrees.
Also of Note is that the Earth's Geographic and Magnetic Poles differ by roughly 11 degrees.
Earth's Wandering Magnetic Poles
The magnetic poles of the Earth are created by its moving molten iron and nickel core. The internal fluid nature of the Earth causes its magnetic poles to move yearly. Over the past 100 years, the pole has moved 1000 km. Presently it is moving over 40 km per year.
The magnetic poles of the Earth are created by its moving molten iron and nickel core. The internal fluid nature of the Earth causes its magnetic poles to move yearly. Over the past 100 years, the pole has moved 1000 km. Presently it is moving over 40 km per year.
Basic Law of Magnetic Forces
Like Poles of magnets repel each other while opposite poles attract each other.
The Nature of Earth's North and South Magnetic Poles.
Like Poles of magnets repel each other while opposite poles attract each other.
The Nature of Earth's North and South Magnetic Poles.
The Magnetic Field
Einstein is said to have been fascinated by a compass as a child, perhaps musing on how the needle felt a force without direct physical contact. His ability to think deeply and clearly about action at a distance, particularly for gravitational, electric, and magnetic forces, later enabled him to create his revolutionary theory of relativity.
Einstein is said to have been fascinated by a compass as a child, perhaps musing on how the needle felt a force without direct physical contact. His ability to think deeply and clearly about action at a distance, particularly for gravitational, electric, and magnetic forces, later enabled him to create his revolutionary theory of relativity.
We have all seen in School that when you sprinkle iron filings around a magnet, the magnetic field lines become visible. There is no analog for this with Electric fields, making magnetic fields a better way to under the idea of a field.
The region surrounding a magnet in which magnetic forces can be exerted is called a magnetic field. Iron filing sprinkled around a magnet reveal the nature of the invisible magnetic field.
The region surrounding a magnet in which magnetic forces can be exerted is called a magnetic field. Iron filing sprinkled around a magnet reveal the nature of the invisible magnetic field.
Since magnetic forces act at a distance, we define a magnetic field to represent magnetic forces. The pictorial representation of magnetic field lines is very useful in visualizing the strength and direction of the magnetic field. The direction of magnetic field lines is defined to be the direction in which the north end of a compass needle points. The magnetic field is traditionally called the B-field.
Magnetic field lines are defined to have the direction that a small compass points when placed at a location. (a) If small compasses are used to map the magnetic field around a bar magnet, they will point in the directions shown: away from the north pole of the magnet, toward the south pole of the magnet. (Recall that the Earth’s north magnetic pole is really a south pole in terms of definitions of poles on a bar magnet.) (b) Connecting the arrows gives continuous magnetic field lines. The strength of the field is proportional to the closeness (or density) of the lines. (c) If the interior of the magnet could be probed, the field lines would be found to form continuous closed loops.
The Vector Nature of a Magnetic Field
When compasses are set in a magnetic field, they show a direction for the magnetic field. Magnetic Fields, like electric fields, are vector quantities showing both magnitude and direction.
The magnetic field lines flow OUT the North pole of the magnetic and INTO the south pole of the magnet (like electric fields flow out of positive charges and into negative - but remember, unlike positive and negative charges, magnetic North and South poles always come together - called dipoles.
When compasses are set in a magnetic field, they show a direction for the magnetic field. Magnetic Fields, like electric fields, are vector quantities showing both magnitude and direction.
The magnetic field lines flow OUT the North pole of the magnetic and INTO the south pole of the magnet (like electric fields flow out of positive charges and into negative - but remember, unlike positive and negative charges, magnetic North and South poles always come together - called dipoles.
Fields Between Attracting and Repelling Poles
The Field Lines Between Attracting poles link together while field lines between repelling poles stay apart.
Review: Comparing Electric and Magnetic Fields
Electric and Magnetic Fields show similar field lines for attracting and repelling fields. Remember the idea of flux or flow.
Because magnetic fields are more visual and tangible than electric fields, it is easier to visualize the idea of a field as a mediator of forces (in this case the magnetic force).
The Field Lines Between Attracting poles link together while field lines between repelling poles stay apart.
Review: Comparing Electric and Magnetic Fields
Electric and Magnetic Fields show similar field lines for attracting and repelling fields. Remember the idea of flux or flow.
Because magnetic fields are more visual and tangible than electric fields, it is easier to visualize the idea of a field as a mediator of forces (in this case the magnetic force).
Geometric / Qualitative Understanding of Magnetic Field Strength or Intensity In Terms of Flux Lines
Intensity of PEMFs is one of the Big Lies in Physics, so we are going to look at it in many ways. First let's start with an geometric and qualitative definition of Magnetic field strength or intensity.
The number of magnetic field lines, referred to as magnetic flux, indicates the strength of the magnetic field and is measured in tesla (T - SI unit). Gauss is also a measure of Magnetic Field strength (1 Tesla = 10,000 Gauss). More on units later.
Again remember electric fields, also the greater the density of lines, the greater the electric flux (greater flux gives rise to a greater force on a test charge).
Intensity of PEMFs is one of the Big Lies in Physics, so we are going to look at it in many ways. First let's start with an geometric and qualitative definition of Magnetic field strength or intensity.
The number of magnetic field lines, referred to as magnetic flux, indicates the strength of the magnetic field and is measured in tesla (T - SI unit). Gauss is also a measure of Magnetic Field strength (1 Tesla = 10,000 Gauss). More on units later.
Again remember electric fields, also the greater the density of lines, the greater the electric flux (greater flux gives rise to a greater force on a test charge).
MAKING CONNECTIONS: CONCEPT OF A FIELD
A field is a way of mapping forces surrounding any object that can act on another object at a distance without apparent physical connection. The field represents the object generating it. Gravitational fields map gravitational forces, electric fields map electrical forces, and magnetic fields map magnetic forces.
A field is a way of mapping forces surrounding any object that can act on another object at a distance without apparent physical connection. The field represents the object generating it. Gravitational fields map gravitational forces, electric fields map electrical forces, and magnetic fields map magnetic forces.
Extensive exploration of magnetic fields has revealed a number of hard-and-fast rules. We use magnetic field lines to represent the field (the lines are a pictorial tool, not a physical entity in and of themselves). The properties of magnetic field lines can be summarized by these rules:
The direction of the magnetic field is tangent to the field line at any point in space. A small compass will point in the direction of the field line.
The strength of the field is proportional to the closeness of the lines. It is exactly proportional to the number of lines per unit area perpendicular to the lines (called the areal density).
Magnetic field lines can never cross, meaning that the field is unique at any point in space. Magnetic field lines are continuous, forming closed loops without beginning or end. They go from the north pole to the south pole.
The last property is related to the fact that the north and south poles cannot be separated. It is a distinct difference from electric field lines, which begin and end on the positive and negative charges. If magnetic monopoles existed, then magnetic field lines would begin and end on them.
The direction of the magnetic field is tangent to the field line at any point in space. A small compass will point in the direction of the field line.
The strength of the field is proportional to the closeness of the lines. It is exactly proportional to the number of lines per unit area perpendicular to the lines (called the areal density).
Magnetic field lines can never cross, meaning that the field is unique at any point in space. Magnetic field lines are continuous, forming closed loops without beginning or end. They go from the north pole to the south pole.
The last property is related to the fact that the north and south poles cannot be separated. It is a distinct difference from electric field lines, which begin and end on the positive and negative charges. If magnetic monopoles existed, then magnetic field lines would begin and end on them.
Ferromagnets
Only certain materials, such as iron, cobalt, nickel, and gadolinium, exhibit strong magnetic effects. Such materials are called ferromagnetic, after the Latin word for iron, ferrum.
A group of materials made from the alloys of the rare earth elements are also used as strong and permanent magnets; a popular one is neodymium.
Not only do ferromagnetic materials respond strongly to magnets (the way iron is attracted to magnets), they can also be magnetized themselves—that is, they can be induced to be magnetic or made into permanent magnets.
Only certain materials, such as iron, cobalt, nickel, and gadolinium, exhibit strong magnetic effects. Such materials are called ferromagnetic, after the Latin word for iron, ferrum.
A group of materials made from the alloys of the rare earth elements are also used as strong and permanent magnets; a popular one is neodymium.
Not only do ferromagnetic materials respond strongly to magnets (the way iron is attracted to magnets), they can also be magnetized themselves—that is, they can be induced to be magnetic or made into permanent magnets.
Domains In a Magnet
When a magnet is brought near a previously unmagnetized ferromagnetic material, it causes local magnetization of the material.
What happens on a microscopic scale is shown here. The regions within the material called domains act like small bar magnets. Within domains, the poles of individual atoms are aligned. Each atom acts like a tiny bar magnet.
Domains are small and randomly oriented in an unmagnetized ferromagnetic object. In response to an external magnetic field, the domains may grow to millimeter size, aligning themselves. This induced magnetization can be made permanent if the material is heated and then cooled, or simply tapped in the presence of other magnets.
When a magnet is brought near a previously unmagnetized ferromagnetic material, it causes local magnetization of the material.
What happens on a microscopic scale is shown here. The regions within the material called domains act like small bar magnets. Within domains, the poles of individual atoms are aligned. Each atom acts like a tiny bar magnet.
Domains are small and randomly oriented in an unmagnetized ferromagnetic object. In response to an external magnetic field, the domains may grow to millimeter size, aligning themselves. This induced magnetization can be made permanent if the material is heated and then cooled, or simply tapped in the presence of other magnets.
Demagnetizing a Magnet
Conversely, a permanent magnet can be demagnetized by hard blows or by heating it in the absence of another magnet. Increased thermal motion at higher temperature can disrupt and randomize the orientation and the size of the domains. There is a well-defined temperature for ferromagnetic materials, which is called the Curie temperature, above which they cannot be magnetized. The Curie temperature for iron is 1043 K (770ºC), which is well above room temperature. There are several elements and alloys that have Curie temperatures much lower than room temperature and are ferromagnetic only below those temperatures.
Conversely, a permanent magnet can be demagnetized by hard blows or by heating it in the absence of another magnet. Increased thermal motion at higher temperature can disrupt and randomize the orientation and the size of the domains. There is a well-defined temperature for ferromagnetic materials, which is called the Curie temperature, above which they cannot be magnetized. The Curie temperature for iron is 1043 K (770ºC), which is well above room temperature. There are several elements and alloys that have Curie temperatures much lower than room temperature and are ferromagnetic only below those temperatures.
Smallest Value in a Magnetically Shielded Room - 10^ -14 Tesla
Interstellar Space 10^-10 Tesla
Human Body Magnetic Field??
Earth's Magnetic Field .00005 Tesla (.5 Gauss)
Sun's Magnetic Field .0001 Tesla (1 Gauss)
*Low Intensity PEMF (Safest and BEST Intensities to Use for PEMF
.00001-.0005 Tesla (.1 - 5 Gauss)
Refrigerator Magnet .01 Tesla (100 Gauss)
*Medium High Intensity PEMF (Not Recommend)
.001-.1 Tesla (10-1000 Gauss)
Good Ceramic Magnet .25 - .4 Tesla (2500-4000 Gauss)
Neodynium Magnet 1.2 - 1.4 Tesla (12,000-14,000 Gauss)
Junkyard Magnets 1 - 2 Tesla (10,000 - 20,000 Gauss
MRI Scanner 1.5 - 2 Tesla (15,000 - 20,000 Gauss)
*High Intensity PEMF - Dangerous and DEFINITELY Not Recommended
1-3Tesla (10,000 - 30,000 Gauss)
Strongest Manmade Magnets are greater than 1000 Tesla
A magnetar is a type of neutron star believed to have the strongest magnetic field in the Universe at 100 Trillion Tesla...
Interstellar Space 10^-10 Tesla
Human Body Magnetic Field??
Earth's Magnetic Field .00005 Tesla (.5 Gauss)
Sun's Magnetic Field .0001 Tesla (1 Gauss)
*Low Intensity PEMF (Safest and BEST Intensities to Use for PEMF
.00001-.0005 Tesla (.1 - 5 Gauss)
Refrigerator Magnet .01 Tesla (100 Gauss)
*Medium High Intensity PEMF (Not Recommend)
.001-.1 Tesla (10-1000 Gauss)
Good Ceramic Magnet .25 - .4 Tesla (2500-4000 Gauss)
Neodynium Magnet 1.2 - 1.4 Tesla (12,000-14,000 Gauss)
Junkyard Magnets 1 - 2 Tesla (10,000 - 20,000 Gauss
MRI Scanner 1.5 - 2 Tesla (15,000 - 20,000 Gauss)
*High Intensity PEMF - Dangerous and DEFINITELY Not Recommended
1-3Tesla (10,000 - 30,000 Gauss)
Strongest Manmade Magnets are greater than 1000 Tesla
A magnetar is a type of neutron star believed to have the strongest magnetic field in the Universe at 100 Trillion Tesla...
Glossary
north magnetic pole:
the end or the side of a magnet that is attracted toward Earth’s geographic north pole
south magnetic pole:
the end or the side of a magnet that is attracted toward Earth’s geographic south pole
ferromagnetic:
materials, such as iron, cobalt, nickel, and gadolinium, that exhibit strong magnetic effects
magnetized:
to be turned into a magnet; to be induced to be magnetic
domains:
regions within a material that behave like small bar magnets
Curie temperature:
the temperature above which a ferromagnetic material cannot be magnetized
magnetic monopoles:
an isolated magnetic pole; a south pole without a north pole, or vice versa (no magnetic monopole has ever been observed)
magnetic field:
the representation of magnetic forces
B-field:
another term for magnetic field
magnetic field lines:
the pictorial representation of the strength and the direction of a magnetic field
direction of magnetic field lines:
the direction that the north end of a compass needle points
Biomagnetism:
When biological material produces an external magnetic field, this is called Biomagnetism
Magnetobiology:
When an external magnetic field is applied to biological material, this is called MAGNETOBIOLOGY.
Magnetoreception:
How organisms detect magnetic fields and usually how they use it for navigation (migratory birds, etc).
north magnetic pole:
the end or the side of a magnet that is attracted toward Earth’s geographic north pole
south magnetic pole:
the end or the side of a magnet that is attracted toward Earth’s geographic south pole
ferromagnetic:
materials, such as iron, cobalt, nickel, and gadolinium, that exhibit strong magnetic effects
magnetized:
to be turned into a magnet; to be induced to be magnetic
domains:
regions within a material that behave like small bar magnets
Curie temperature:
the temperature above which a ferromagnetic material cannot be magnetized
magnetic monopoles:
an isolated magnetic pole; a south pole without a north pole, or vice versa (no magnetic monopole has ever been observed)
magnetic field:
the representation of magnetic forces
B-field:
another term for magnetic field
magnetic field lines:
the pictorial representation of the strength and the direction of a magnetic field
direction of magnetic field lines:
the direction that the north end of a compass needle points
Biomagnetism:
When biological material produces an external magnetic field, this is called Biomagnetism
Magnetobiology:
When an external magnetic field is applied to biological material, this is called MAGNETOBIOLOGY.
Magnetoreception:
How organisms detect magnetic fields and usually how they use it for navigation (migratory birds, etc).