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----------------------------- 2341 - Magnetism – from Atoms to Stars
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- Magnetism is one manifestation of the electromagnetic force, which is one of the four forces known in the universe. Light is another manifestation of electromagnetic energy that propagates through space with electric waves and magnetic waves switching back and forth at right angles to each other, traveling through space at a constant speed of 670,633,500 miles per hour.
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- The speed at which the electromagnetic waves switch back and forth determines how we observe the energy. If this speed, or frequency, is faster than light wave frequencies than we observe ultraviolet, x-ray, then gamma ray energy.
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- If the switching speed is slower than we observe microwaves, and radio waves. The frequency is how fast the energy is switching through time. The electromagnetic wave’s speed through Space is constant, 300,000,000 meters / second.
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- The frequency of yellow light is 500,000,000,000 switches / second. The frequency of radio is 300,000,000 switches / second.
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- In 1831 Michael Faraday first showed the relationship between magnetic and electric energy. Faraday demonstrated that a bar magnetic passed through a coil of wire generated an electric current in the wire. Motion through space, with the magnetic lines of force cutting across the wire set up the electric current.
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- The motionless magnet has no electric affect. In reverse, the coil of wire around an iron core can create a magnetic field, as long as the electrons are in motion as current through the wire.
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- But, what about a stationary permanent magnetic that has a magnetic field without any electric current or motion involved? There are still electrons in motion. Magnetism is a property of the atom itself.
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- In that sense all material that we know of is magnetic at some level. The electrons spin about the atom and the electrons themselves spin so that each atom becomes a tiny atomic magnet.
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- In most materials these atomic magnets are oriented in random directions and there is no net magnetic affect that we can easily detect. However, some materials such as iron and nickel have the capacity to orient their atomic structure in such a way that the poles of the tiny magnets are lined up in the same direction.
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- Permeability is the measure of magnetic strength of material. A vacuum is given a permeability of 1.00. Ordinary material with weak magnetic properties may have a permeability of 1.01.
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------------------------------------------ Permeability:
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--------------------------------------- Iron = 1000
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--------------------------------------- Nickel = 40
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--------------------------------------- Cobalt = 55
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- In these stronger magnetic substances there are magnetic domains 0.001 to 0.1 centimeters in diameter where the tiny atomic magnets are oriented in the same direction reinforcing each other and creating an overall strong magnetic field.
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- Because the Earth has an iron core it was once thought that the Earth was a giant permanent magnetic because of the magnetic field that completely surrounds the Earth.
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- The Earth has an iron core but it cannot be a permanent magnetic because it is molten and iron loses its strong magnetic properties at 1033 degrees Kelvin. The higher temperatures and vibrating atoms destroys the magnetic domains. The Earth’s core is 6500 degrees Kelvin ( For example, the Sun’s surface is 5,800 degrees Kelvin ).
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- However, the Earth’s core is in two parts, an inner solid core and an outer molten core. The inner core is iron and nickel, while the outer core is molten iron, nickel and sulfur. These two cores do not rotate at the same speed. The inner core rotates faster while the outer molten core is slowed down by friction of the mass and weight above it.
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- It is this rotating metallic core that creates the magnetic field around the Earth. The strength of the field is currently weakening. It will continue to weaken and eventually it will reverse North-South polarity, then strengthen again.
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- By studying the crystal alignment in rocks we can see that older rocks were magnetized in the direction opposite to Earth’s present magnetic field. In fact, the Global Rift on the ocean floor shows magnetic reversals occurring every 50,000 to 20,000,000 years with the pattern on one side of the rift mirror-imaged on the other side.
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- The Earth has switched its polarity nine times over the past 4 million years. The last polarity switch occurred 780,000 years ago. Since then the magnetic strength has weakened and strengthened several gauss fourteen times without a polarity reversal. If we drill core samples out of the ocean sediment we can identify 171 polarity reversals during the last 78 million years.
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- The smallest magnets are used in computer memory disks. These disks have a metallic surface film that stores digital information in small magnetic domains. These tiny regions of magnetic material can span only tens of atoms on an edge.
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- In the magnetic storage material, each atom acts as a minuscule bar magnetic due to the property of spin. In the storage media of each magnetic domain, almost all of the atoms have the same one of two possible spin orientations. These two possibilities serve as the ones and zeros of digital information. The most advanced magnetic disks use magnetic domains comparable in size to a large virus, 200 nanometers by 10 nanometers in area (nanometer = 10^-9 meters).
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- Theory is that magnetic domains smaller than 10 nanometers on a side will be unable to maintain their spin orientation to store these ones and zeros unless the media is chilled well below room temperature.
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- Scientists have used Scanning Tunneling Microscopes to detect atomic spins in less than 10 nanometer wide domains. These tiny domains were in ultrathin films of iron deposited on a tungsten backing cooled to 16 degrees Kelvin. Scanning Tunneling Microscopes may someday serve as the reading head of future disk drives.
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- To go from the smallest magnets to the largest we need to compare the relative strengths of magnetic fields using the unit of measurement for magnetic flux density, the gauss:
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- Despite the fact that magnetic lines of force have no material existence, it is often convenient to picture them in a literal fashion in order to describe a magnetic field. The strength of a magnetic field is described as the number of lines of force passing through an area of unit size.
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- This is called the magnetic flux density. The flux density measures how closely the lines of force are crowded together. The more closely they crowd, the higher the flux density and the stronger the magnetic field at that point. We define one line of force as one Maxwell. And, the unit of flux density as one Maxwell per square centimeter as one gauss.
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--------------------------------------------------------------- Gauss
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----------- Weakest sustainable in the lab 0.00000000008
----------- The brain’s magnetic field 0.00000002
----------- Interstellar galactic space 0.000001
----------- Produced by the human body 0.000003
----------- Refrigerator 0.001
----------- Electric lamp 0.01
----------- Household wiring 0.1
----------- The Milky Way 0.2
----------- Earth’s field at the poles 0.6
----------- Sun’s magnetic field 2.0
----------- Jupiter’s magnetic field 4.3
----------- TV set 5
----------- Electric shaver 10
----------- Hairdryer 25
----------- Typical refrigerator magnet 100
----------- Sunspots 3000
----------- Largest man-made permanent magnet 50,000
----------- Strongest sustainable in the lab 387,000
----------- Strongest found in normal stars 1,000,000
----------- Strongest for < second in lab 10,000,000
----------- Magnetic white dwarf star 200,000,000
----------- Surface of atomic nucleus 10,000,000,000
----------- Normal neutron star 5,000,000,000,000
----------- Magnetar neutron star 1,000,000,000,000,000 10^15 gauss
----------- Strongest field possible in theory 10^53 gauss
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- To go from the smallest to the very largest magnetic fields we need to go from atoms to stars. The Magnetar produces the strongest magnetic fields known in the Universe. It is a star that is 30 to 100 times the mass of our Sun.
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- These massive stars do not live very long, 1 to 10 million years, before they burn all their hydrogen, then helium, then carbon, then oxygen, then silicon fuel. The next fusion is iron and it cannot generate energy with further fusion. So, the outward pressure stops and the star collapses under the force of gravity. The center of the star becomes so massive it collapses itself into a black hole.
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- The material feeding the black hole forms a disk of high speed particles spinning at light speeds. In 10 seconds after the collapse begins the spinning disk generates magnetically confined jets that explode out the poles of the star in cone shaped shock waves. These concentrated energies aim magnetic fields in the two directions, ex: north and south. The jets are only 2 to 5 degrees wide.
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- As the shock waves blast through particles from the star gamma rays are produced. As the jets slow down from plowing into interstellar material lower energy radiation is also produced in the form of x-ray, optical, and radio afterglow’s that last from minutes to months.
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- Astronomers observe one of these events each day on average, coming from all directions in the Universe. Because the beams are only two to five degrees wide that means there are 1000 bursts invisible to us because they are pointing in another direction. Statistically that means we average 1500 supernova bursts of this magnitude occurring every day.
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- The magnetic strength of a magnetar neutron star is powerful enough to rip at kitchen knife out of your hand from a distance that is half way to the moon. Not only could it erase your credit cards, it could pull the iron out of your blood.
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- We know that an asteroid struck Mexico 65 million years ago annihilating the dinosaurs that ruled the Earth at that time. There was another devastating mass extinction at the end of the Ordovician period 440 million years ago. During the Ordovician period all life on Earth was aquatic, and fossil records show that species living in deeper water fared better than shallow-water dwellers.
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- One possible explanation is that a magnetar neutron star focused its radiation at Earth breaking apart the atmosphere molecules that protect us from the Sun’s ultraviolet radiation. This would explain the death of creatures near the water’s surface. The same phenomena could explain a similar mass extinction that occurred to start the Cambrian period 544 million years ago.
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- Most of these gamma ray jets pass by unseen, but occasionally one is pointed right at us, as if we were sitting at the end of a gun barrel. Let’s hope the gun is not too close.
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- The metric unit of magnetism is named after Johann Karl Friedrich Gauss who was born in 1877 in Brunswick, Germany. His father was a gardener and his mother a servant girl. Johann was a genius in mathematics at a young age. At three years old he could correct math mistakes and keep all sorts of numerical records in his head.
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- He became one of the world’s three greatest mathematicians, Archimedes and Isaac Newton being the other two. At age 22 he received his Ph D from Gottingen University. As a student he calculated the orbit of the asteroid, Ceres, to allow it to be located after it was lost. Johann also worked out the location of the planet Neptune to allow it to be discovered in 1846.
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- In 1842 he devised the set of units of measuring magnetism and the unit for magnetic flux density was eventually named the gauss. His work with terrestrial magnetism allowed him to calculate the location of the magnetic poles on Earth, which proved to be remarkable accurate.
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- Johann even constructed an electric telegraph in 1833, about the same time Joseph Henry invented the telegraph in the United States.
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- April 24, 2019. 32
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--------------------- Thursday, April 25, 2019 -------------------------
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