There are four fundamental forces which govern our universe.
One of these is electromagnetism. Like two sides of the same coin, electrical and magnetic fields
coexist together, and when positive and negative particles interact together,
like the nucleus and electrons of an atom, an electromagnetic field is created. This field
holds atoms together, creates molecular bonds, and governs chemical reactions. At a macroscopic scale,
magnetic fields protect life on planet Earth from dangerous high-energy solar wind. Magnetometry the
study of magnetic fields, has allowed humans to unlock geologic mysteries, understand the universe,
and even create anti-gravity technologies. I'm your host Stefan and welcome to Geophysics Explained.
Most people have experience with magnetic fields by having played with a magnet. A magnet has a
positive north pole and a negative south pole each attracted to the other. A positive pole will repel
another positive pole and this relationship is true for negative poles as well. At the
atomic level a magnet is surrounded in space by an invisible magnetic field created by the movement
of electrons. The activity of these electrons gives magnets their ability to attract and repel.
Electricity and magnetism are linked down to the quantum level and when an electric current is
created and electrons are in flow a magnetic field is created. Likewise permanent magnetic fields can
guide the flow of electrons. It is in this way that a fluxgate magnetometer a device able to
measure magnetic fields works. Inside a fluxgate magnetometer electromagnets are used to measure
magnetic fields. When a bar of ferromagnetic metal is wrapped in a wire and an electric current
is run through the wire, the bar magnetizes and generates a magnetic field. Reverse the current and
the magnetic field reverses as well. Together these two induced magnetic fields cancel each other out,
but when in the presence of an external magnetic field, the alternating induced fields are
shifted and the external field can be measured. With sensors oriented in X Y and Z directions
the local magnetic field can be measured in all three dimensions.
Before the advent of modern magnetometers which are capable of sampling the magnetic field
hundreds or even thousands of times per second, simpler technologies were used like the compass.
Compass technology revolutionized the world when it began to be used for navigation in the 11th
century and its use is simple. When suspended in water the magnetized pin of a compass lines up
with the magnetic field lines of our planet each end pointing to the oppositely charged magnetic
pole of the Earth. In the presence of a more powerful magnetic field the compass needle will
point towards that magnetic pole instead. On Mars for example, which has no planetary wide magnetic
field, an explorer with the compass traversing the Martian landscape would observe it rotating
from one local magnetic anomaly to another. Back on Earth the north side of a compass points to
the Earth's negative magnetic pole which is in fact located in the northern hemisphere.
It is a common misconception that the magnetic positive north pole is in the northern hemisphere.
Currently the earth's magnetic north pole is located in the southern hemisphere.
The magnetic field of the earth over geologic time regularly goes through magnetic pole reversals.
At seafloor spreading centers deep underwater magma spews out and cools into a rock known as basalt.
Due to its mafic iron-rich composition basalt is faintly magnetic. As it cools in temperature below
its curie point it magnetizes in the direction of the local magnetic field, which is the Earth's
magnetic field, giving it a unique magnetic signature. Geophysicists first observed this
magnetic striping in the 1950s and since have used the data to chronicle the magnetic cycles of Earth
using radiometric dating. The record shows that the magnetic field of the Earth can flip quite rapidly
and then remain stable for hundreds of thousands or millions of years before flipping back.
Like the earth the Sun also undergoes magnetic pole reversals but at a much higher frequency of
approximately once every 11 years. The Sun's changing magnetic field influences how much
energy it releases into space and you can learn more about how solar magnetism affects Earth's
climate by watching my Geophysics Explained video on solar cycles. Magnetometry has unlocked other
geologic mysteries too. As Greenland traveled over the Iceland hotspot 80 to 40 million years ago
the volcanism that occurred altered the rocks and therefore their magnetism.
As the volcanism died down the curie point was passed with high temperature basaltic magma having
no permanent magnetism cooling into basaltic rocks which gained permanent magnetic properties.
From magnetic observations geothermal heat flux data was derived and the motion of Greenland
over geologic time due to plate tectonics was inferred. Geophysicists around the world utilize
magnetometry to better understand the structure of the Earth and explore from minerals, while
other scientists utilize magnetics for uses as diverse as brain imaging
and particle acceleration. Magnetism can change your perception of what's possible.
As one of the four fundamental forces of nature electromagnetic force can be used to resist the
power of gravity another fundamental force of nature. This is known as magnetic levitation
and while it seems like magic it's the reality that we live in. Maglev trains for example utilize
the power of opposing magnetic fields to reduce friction and increase speed. At smaller scales
magnetic levitation is easily observed with a few different methods. To understand how magnetic
levitation works it's best to first understand the difference between diamagnetism and paramagnetism.
Diamagnetic materials are repelled by magnetic fields when a magnetic field is applied to a
diamagnetic material, an induced field is created in the opposite direction, creating
a repulsive force. All materials have some degree of diamagnetism but the repulsive diamagnetic
force will only be dominant if these materials do not also exhibit paramagnetism or ferromagnetism.
Superconductors and natural diamagnetic materials strongly oppose external magnetic fields and since
the electromagnetic force is more powerful than the force of gravity mid-air levitation
can occur. Alternatively when certain materials are sufficiently cooled with liquid nitrogen
they become superconductors repelling all magnetic field lines from flowing through their structure
and in this example causing the powerful neodymium magnet sitting on top of it to lift off and float
in mid-air until the superconducting material warms up sufficiently, losing its superconducting
status. In contrast to diamagnetism, paramagnetic materials are weakly attracted to externally
applied magnetic fields forming internally induced magnetic fields in the direction of the applied
field. Unpaired electrons are the cause as the spin of an unpaired electron creates a magnetic dipole
and therefore a tiny magnetic field. An externally applied magnetic field causes the magnetic dipoles
of the unpaired electrons to align parallel to the field and create an attractive force. Most chemical
elements and some compounds are paramagnetic due to the presence of unpaired electrons
and this phenomenon is well observed with liquid oxygen. When pouring liquid oxygen onto a strong
magnet the liquid oxygen is temporarily attracted to the strong magnetic field of the magnet,
aligning its unpaired electrons parallel to the field. Thermal random motion dealigns the magnetic
fields of the unpaired electrons and that's why paramagnetism is stronger at lower temperatures
as this de-alignment is reduced. As the supercooled liquid oxygen evaporates into a
gas at room temperature the paramagnetic effect greatly reduces and the visible phenomenon ends.
Ferromagnetism is the type of magnetism everyone is most familiar with. Ferromagnetic materials like
Iron Cobalt and Nickel have permanently aligned magnetic dipoles. In the presence of a strong
externally applied magnetic field, a ferromagnetic object will be attracted to the field and attach
itself to the magnet. A simple way to determine if something is diamagnetic paramagnetic or
ferromagnetic is to examine the electrons. If all electrons are paired then diamagnetism is a result.
If there are unpaired electrons then paramagnetism is the dominant result.
If the unpaired electrons are permanently aligned then ferromagnetism is a result.
The knowledge of diamagnetism paramagnetism and ferromagnetism helps one to understand
the nature of our existence better. Take breathing for example. We know that oxygen is paramagnetic
and that the heart has a magnetic field. When breathing there is a minor paramagnetic
effect between oxygen flowing into the lungs and the magnetic field of the heart.
The level of induced magnetization is very small because only a fraction of the oxygen's unpaired
electron dipoles will orient to the magnetic field of the heart. The strength of the external
magnetic field and the temperature of the oxygen gas determine how many unpaired electron dipoles
align to the heart's magnetic field, but when breathing this paramagnetic effect does exist,
Hindus call this effect Prana. So the next time you pick up a magnet or even take a
breath consider the quantum physics which enables magnetism and therefore our universe to exist.
I hope you all enjoyed learning more about electromagnetism
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Geophysics Explained videos. I've been your host Stefan Burns, thanks so much for watching :)