[/caption]Magnetism is a fundamental force of the universe, essential to its function and existence in the same way that gravity and weak and strong nuclear forces are. But interestingly enough, there are several different kinds of magnetism. For example, there is ferromagnetism, a property which applies to super magnets, where magnetic properties exist regardless of whether or not there is a magnetic field acting on the material itself. There is also Diamagnetism, which refers to materials that are not affected by a magnetic field, and Paramagnetism, a form of magnetism that occurs only in the presence of an externally applied magnetic field.
Materials that are called ‘paramagnets’ are most often those that exhibit, at least over an appreciable temperature range, magnetic susceptibilities that adhere to the Curie or Curie–Weiss laws. According to these laws, which apply at low-levels of magnetization, the susceptibility of paramagnetic materials is inversely proportional to their temperature. Mathematically, this can be expressed as: M = C(B/T), where M is the resulting magnetization, B is the magnetic field, T is absolute temperature, measured in kelvins, C is a material-specific Curie constant.
Paramagnets were named and extensively researched by British scientist Michael Faraday – the man who gave us Faraday’s Constant, Faraday’s Law, the Faraday Effect, etc. – beginning in 1845. He, and many scientists since, found that certain material exhibited what was commonly referred to as “negative magnetism”. Most elements and some compounds are paramagnetic, with strong paramagnetism being exhibited by compounds containing iron, palladium, platinum, and certain rare-earth elements. In such compounds atoms of these elements have some inner electron shells that are incomplete, causing their unpaired electrons to spin like tops and orbit like satellites. This makes the atoms act like a permanent magnet, tending to align with and hence strengthen an applied magnetic field. However, once the magnetic field is removed, the atoms fall out of alignment and the material return to its original state. Strong paramagnetism also decreases with rising temperature because of the de-alignment produced by the greater random motion of the atomic magnets.
Weak paramagnetism, independent of temperature, is found in many metallic elements in the solid state, such as sodium and the other alkali metals. Other examples include Iron oxide, Uranium, Platinum, Tungsten, Cesium, Aluminum, Lithium, Magnesium, Sodium, and Oxygen gas. Even iron, a highly magnetic material, can become a paramagnet once it is heated above its relatively high Curie-point.
We have written many articles about magnetism for Universe Today. Here’s an article about magnetic field, and here’s an article about what magnets are made of.
If you’d like more info on paramagnetism, check out these articles from Hyperphysics and Physlink.
Artist's conception of the event horizon of a black hole. Credit: Victor de Schwanberg/Science Photo Library
Ever since scientists first discovered the existence of black holes in our universe, we have all wondered: what could possibly exist beyond the veil of that terrible void? In addition, ever since the theory of General Relativity was first proposed, scientists have been forced to wonder, what could have existed before the birth of the Universe – i.e. before the Big Bang?
Interestingly enough, these two questions have come to be resolved (after a fashion) with the theoretical existence of something known as a Gravitational Singularity – a point in space-time where the laws of physics as we know them break down. And while there remain challenges and unresolved issues about this theory, many scientists believe that beneath veil of an event horizon, and at the beginning of the Universe, this was what existed.
Definition:
In scientific terms, a gravitational singularity (or space-time singularity) is a location where the quantities that are used to measure the gravitational field become infinite in a way that does not depend on the coordinate system. In other words, it is a point in which all physical laws are indistinguishable from one another, where space and time are no longer interrelated realities, but merge indistinguishably and cease to have any independent meaning.
This artist’s impression depicts a rapidly spinning supermassive black hole surrounded by an accretion disc. Credit: ESA/Hubble, ESO, M. Kornmesse
Origin of Theory:
Singularities were first predicated as a result of Einstein’s Theory of General Relativity, which resulted in the theoretical existence of black holes. In essence, the theory predicted that any star reaching beyond a certain point in its mass (aka. the Schwarzschild Radius) would exert a gravitational force so intense that it would collapse.
At this point, nothing would be capable of escaping its surface, including light. This is due to the fact the gravitational force would exceed the speed of light in vacuum – 299,792,458 meters per second (1,079,252,848.8 km/h; 670,616,629 mph).
This phenomena is known as the Chandrasekhar Limit, named after the Indian astrophysicist Subrahmanyan Chandrasekhar, who proposed it in 1930. At present, the accepted value of this limit is believed to be 1.39 Solar Masses (i.e. 1.39 times the mass of our Sun), which works out to a whopping 2.765 x 1030 kg (or 2,765 trillion trillion metric tons).
Another aspect of modern General Relativity is that at the time of the Big Bang (i.e. the initial state of the Universe) was a singularity. Roger Penrose and Stephen Hawking both developed theories that attempted to answer how gravitation could produce singularities, which eventually merged together to be known as the Penrose–Hawking Singularity Theorems.
The Big Bang Theory: A history of the Universe starting from a singularity and expanding ever since. Credit: grandunificationtheory.com
According to the Penrose Singularity Theorem, which he proposed in 1965, a time-like singularity will occur within a black hole whenever matter reaches certain energy conditions. At this point, the curvature of space-time within the black hole becomes infinite, thus turning it into a trapped surface where time ceases to function.
The Hawking Singularity Theorem added to this by stating that a space-like singularity can occur when matter is forcibly compressed to a point, causing the rules that govern matter to break down. Hawking traced this back in time to the Big Bang, which he claimed was a point of infinite density. However, Hawking later revised this to claim that general relativity breaks down at times prior to the Big Bang, and hence no singularity could be predicted by it.
Some more recent proposals also suggest that the Universe did not begin as a singularity. These includes theories like Loop Quantum Gravity, which attempts to unify the laws of quantum physics with gravity. This theory states that, due to quantum gravity effects, there is a minimum distance beyond which gravity no longer continues to increase, or that interpenetrating particle waves mask gravitational effects that would be felt at a distance.
Types of Singularities:
The two most important types of space-time singularities are known as Curvature Singularities and Conical Singularities. Singularities can also be divided according to whether they are covered by an event horizon or not. In the case of the former, you have the Curvature and Conical; whereas in the latter, you have what are known as Naked Singularities.
A Curvature Singularity is best exemplified by a black hole. At the center of a black hole, space-time becomes a one-dimensional point which contains a huge mass. As a result, gravity become infinite and space-time curves infinitely, and the laws of physics as we know them cease to function.
Conical singularities occur when there is a point where the limit of every general covariance quantity is finite. In this case, space-time looks like a cone around this point, where the singularity is located at the tip of the cone. An example of such a conical singularity is a cosmic string, a type of hypothetical one-dimensional point that is believed to have formed during the early Universe.
And, as mentioned, there is the Naked Singularity, a type of singularity which is not hidden behind an event horizon. These were first discovered in 1991 by Shapiro and Teukolsky using computer simulations of a rotating plane of dust that indicated that General Relativity might allow for “naked” singularities.
In this case, what actually transpires within a black hole (i.e. its singularity) would be visible. Such a singularity would theoretically be what existed prior to the Big Bang. The key word here is theoretical, as it remains a mystery what these objects would look like.
For the moment, singularities and what actually lies beneath the veil of a black hole remains a mystery. As time goes on, it is hoped that astronomers will be able to study black holes in greater detail. It is also hoped that in the coming decades, scientists will find a way to merge the principles of quantum mechanics with gravity, and that this will shed further light on how this mysterious force operates.
[/caption]Overcoming the pull of gravity and fighting acceleration are major challenges for scientists looking to achieve flight and/or high-speed transportation. One way that they overcome this is the modern and growing technology known as Magnetic Levitation. Relying on rare earth magnets, superconductors, electromagnets and diamagnets, magnetic levitation is now used for maglev trains, magnetic bearings and for product display purposes. Today, maglev transportation is one of the fastest growing means of transportation in industrialized countries. This method has the potential to be faster, quieter and smoother than wheeled mass transit systems and the power needed for levitation is usually not a particularly large percentage of the overall consumption; most of it being used to overcome air drag. In William Gibson’s novel Spook Country, maglev technology was also featured in the form of a “maglev bed”, a bed which used magnets to stay suspended in midair.
Magnetic levitation (aka. maglev or magnetic suspension) is the method by which an object is suspended with no support other than magnetic fields. According to Earnshaw’s theorem (a theory which is usually referenced to magnetic fields), it is impossible to stably levitate against gravity relying solely on static ferromagnetism. However, maglev technology overcomes this through a number of means. These include, but are not limited to, mechanical constraint (or pseudo-levitation), diamagnetism levitation, superconductors, rotational stabilization, servomechanisms, induced currents and strong focusing.
Pseudo-levitation relies on two magnets that are mechanically arranged to repel each other strongly, or are attracted but constrained from touching by a tensile member, such as a string or cable. Another example is the Zippe-type centrifuge where a cylinder is suspended under an attractive magnet, and stabilized by a needle beading from below. Diamagnetic levitation occurs when diamagnetic material is placed in close proximity to material that produces a magnetic field, thus repelling the diamagnetic material. Superconductor-levitation is achieved much the same way, superconductors being a perfect diamagne. Due to the Meissner effect, superconductors also have the property of having completely expelled their magnetic fields, allowing for further stability.
The first commercial maglev people mover was simply called “MAGLEV” and officially opened in 1984 near Birmingham, England. It operated on an elevated 600-metre (2,000 ft) section of monorail track between Birmingham International Airport and Birmingham International railway station, running at speeds up to 42 km/h (26 mph). Perhaps the most well-known implementation of high-speed maglev technology currently in operation is the Shanghai Maglev Train, a working model of the German-built Transrapid train that transports people 30 km (19 mi) to the airport in just 7 minutes 20 seconds, achieving a top speed of 431 km/h and averaging 250 km/h.
We have written many articles about magnetic levitation for Universe Today. Here’s an article about the uses of electromagnets, and here’s an article about how magnets work.
If you’d like more info on the magnetic levitation, check out these articles from How Stuff Works and Hyperphysics.
[/caption]A magnetic field is a pretty awesome thing. As a fundamental force of the universe, they are something without which, planetary orbits, moving electrical charges, or even elementary particles could not exist. It is therefore intrinsic to scientific research that we be able to generate magnetic fields ourselves for the purpose of studying electromagnetism and its fundamental characteristics. One way to do this is with a device known as the Helmholtz Coil, an instrument that is named in honor of German physicist Hermann von Helmholtz (1821-1894), a scientist and philosopher who made fundamental contributions to the fields of physiology, optics, mathematics, and meteorology in addition to electrodynamics.
A Helmholtz coil is a device for producing a region of nearly uniform magnetic field. It consists of two identical circular magnetic coils that are placed symmetrically, one on each side of the experimental area along a common axis, and separated by a distance (h) equal to the radius (R) of the coil. Each coil carries an equal electrical current flowing in the same direction. A number of variations exist, including use of rectangular coils, and numbers of coils other than two. However, a two-coil Helmholtz pair is the standard model, with coils that are circular and in shape and flat on the sides. In such a device, electric current is passed through the coil for the purpose of creating a very uniform magnetic field.
Helmholtz coils are used for a variety of purposes. In one instance, they were used in an argon tube experiment to measure the charge to mass ratio (e:m)of electrons. In addition, they are often used to measure the strength and fields of permanent magnets. In order to do this, the coil pair is connected to a fluxmeter, a device which contains measuring coils and electronics that evaluate the change of voltage in the measuring coils to calculate the overall magnetic flux.In some applications, a Helmholtz coil is used to cancel out Earth’s magnetic field, producing a region with a magnetic field intensity much closer to zero. This can be used to see how electrical charges and magnetic fields operate when not acted on by the gravitational pull of the Earth or other celestial bodies.
In a Helmholtz girl, the magnetic flux density of a field generated (represented by B) can be expressed mathematically by the equation:
Where R is the radius of the coils, n is the number of turns in each coil, I is the current flowing through the coils, and ?0 is the permeability of free space (1.26 x 10-6 T • m/A).
We have written many articles about the Helmholtz Coil for Universe Today. Here’s an article about the right hand rule magnetic field, and here’s an article about magnetic field.
If you’d like more info on the Helmholtz Coil, check out an article from Hyperphysics. Also, here’s another article about the Helmholtz Coil.
[/caption]It has long been known that all molecules possess two equal and opposite charges which are separated by a certain distance. This separation of positive and negative charges is what is referred to as an electric dipole, meaning that it essentially has two poles. In the case of such polar molecules, the center of negative charge does not coincide with the center of positive charge. The extent of polarity in such covalent molecules can be described by the term Dipole Moment, which is essentially the measure of polarity in a polar covalent bond.
The simplest example of a dipole is a water molecule. A molecule of water is polar because of the unequal sharing of its electrons in a “bent” structure. The water molecule forms an angle, with hydrogen atoms at the tips and oxygen at the vertex. Since oxygen has a higher electronegativity than hydrogen, the side of the molecule with the oxygen atom has a partial negative charge while the hydrogen, in the center, has a partial positive charge. Because of this, the direction of the dipole moment points towards the oxygen.
In the language of physics, the electric dipole moment is a measure of the separation of positive and negative electrical charges in a system of charges, that is, a measure of the charge system’s overall polarity – i.e. the separation of the molecules electric charge, which leads to a dipole. Mathematically, and in the simple case of two point charges, one with charge +q and one with charge ?q, the electric dipole moment p can be expressed as:p=qd, where d is the displacement vector pointing from the negative charge to the positive charge. Thus, the electric dipole moment vector p points from the negative charge to the positive charge.
Another way to look at it is to represent the Dipole Moment by the Greek letter m, m = ed, where e is the electrical charge and d is the distance of separation. It is expressed in the units of Debye and written as D (where 1 Debye = 1 x 10-18e.s.u cm). A dipole moment is a vector quantity and is therefore represented by a small arrow with a tail at the positive center and head pointing towards a negative center. In the case of a Water molecule, the Dipole moment is 1.85 D, whereas a molecule of hydrochloric acid is 1.03 D and can be represented as:
We have written many articles about dipole moment for Universe Today. Here’s an article about what water is made of, and here’s an article about molecules.
If you’d like more info on dipole moment, check out these articles from Hyperphysics and Science Daily.
We’ve also recorded an entire episode of Astronomy Cast all about Molecules in Space. Listen here, Episode 116: Molecules in Space.
Saturn has fascinated amateurs and professionals alike for centuries. As quickly as the planet’s ring system was discovered the popular question became ‘why does Saturn have rings?’ usually followed by ‘what are Saturn’s rings made of?’. Well, here are the answers to both questions.
The simplest answer as to why Saturn has rings and what they are made of is that the planet has accumulated a great deal of dust, particles, and ice at varying distances from its surface. These items are most likely trapped by gravity. The rings appear because of the wavelengths of light reflected by these rings of debris.
Some scientists speculate that Saturn may be too big. Its gravitational pull is so strong that it has been able to snatch debris from space. Some of which is as large as an entire building. That pull is why it has at least 62 moons. Those moons contribute dust to the rings as well as absorb dust from the rings.
A common theory as to how all of the material initially accumulated in Saturn’s rings is a series of asteroid impacts. Not with the planet, but with the moons around it. After the impact the remnants of the asteroids and the debris from the moons could not escape the gravitational pull of the planet.
One other theory holds that the rings of Saturn formed as other moons broke apart in ancient times. Additionally, this theory states that some of the material could be from earlier, during the formation of the solar system, and Saturn could not accrete the material while it was forming and it has been in orbit ever since.
No matter which theory you believe, the rings of Saturn are spectacular. After researching Saturn’s rings a little more, be sure to investigate the ring systems around Neptune, Uranus, and Jupiter. Each system is fainter than Saturn’s, but still interesting.
We have written many articles about Saturn for Universe Today. Here’s an article about the color of Saturn, and here are some pictures of Saturn.
When it comes to physics, the concept of energy is a tricky thing, subject to many different meanings and dependent on many possible contexts. For example, when speaking of atoms and particles, energy comes in several forms, such as electrical energy, heat energy, and light energy.
But when one gets into the field of quantum mechanics, a far more complex and treacherous realm, things get even trickier. In this realm, scientists rely on concepts such as Fermi Energy, a concept that usually refers to the energy of the highest occupied quantum state in a system of fermions at absolute zero temperature.
Fermions:
Fermions take their name from famed 20th century Italian physicist Enrico Fermi. These are subatomic particles that are usually associated with matter, whereas subatomic particles like bosons are force carriers (associated with gravity, nuclear forces, electromagnetism, etc.) These particles (which can take the form of electrons, protons and neutrons) obey the Pauli Exclusion Principle, which states that no two fermions can occupy the same (one-particle) quantum state.
Neils Bohr’s model a nitrogen atom. Credit: britannica.com
In a system containing many fermions (like electrons in a metal), each fermion will have a different set of quantum numbers. Fermi energy, as a concept, is important in determining the electrical and thermal properties of solids. The value of the Fermi level at absolute zero (-273.15 °C) is called the Fermi energy and is a constant for each solid. The Fermi level changes as the solid is warmed and as electrons are added to or withdrawn from the solid.
Calculating Fermi Energy:
To determine the lowest energy a system of fermions can have (aka. it’s lowest possible Fermi energy), we first group the states into sets with equal energy, and order these sets by increasing energy. Starting with an empty system, we then add particles one at a time, consecutively filling up the unoccupied quantum states with the lowest energy.
When all the particles have been put in, the Fermi energy is the energy of the highest occupied state. What this means is that even if we have extracted all possible energy from a metal by cooling it to near absolute zero temperature (0 kelvin), the electrons in the metal are still moving around. The fastest ones are moving at a velocity corresponding to a kinetic energy equal to the Fermi energy.
Image showing bosons, fermions and other particles created by a high-energy collision. Credit: CERN
Applications:
The Fermi energy is one of the important concepts of condensed matter physics. It is used, for example, to describe metals, insulators, and semiconductors. It is a very important quantity in the physics of superconductors, in the physics of quantum liquids like low temperature helium (both normal and superfluid 3He), and it is quite important to nuclear physics and to understand the stability of white dwarf stars against gravitational collapse.
Confusingly, the term “Fermi energy” is often used to describe a different but closely-related concept, the Fermi level (also called chemical potential). The Fermi energy and chemical potential are the same at absolute zero, but differ at other temperatures.
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Everyone knows that tornadoes are among nature’s most powerful and destructive phenomenon on land. Also just like other types of storms tornadoes are ranked by strength. The way that tornadoes are ranked is using the Fujita scale. The Fujita scale is a scale that measures the strength of a tornado by the speed of the winds and the amount of the destruction that it causes. The scale is not perfect in that it is hard to directly measure the speeds of the winds and when looking at damage the guidelines are very general and damage becomes indistinguishable after F3.
The Fujita scale is no longer in use since scientists agreed decommission it in favor of the Enhanced Fujita scale, a more nuanced version of the scale that better ranks tornadoes with detailed guidelines concerning wind and destruction patterns. The Fujita scale is still useful to the average person in giving them a general idea of the strength of a tornado. The interesting thing to look for in the Fujita scale is when it reaches F6 tornado. The F6 is a mythical tornado that you would likely only see in movies or hear of in tall tales. It is similar to the magnitude 10 tornado. Early history may have witnessed such phenomena but they have not occurred in modern times due to more settled climates.
The F6 tornado would be the granddaddy of all tornadoes. It would have wind speeds exceeding 300 miles per hour at maximum and would be able to lift houses from their foundations like Dorothy’s Kansas home in the Wizard of Oz. Car would become ballistic missiles able to hurl at tremendous speeds. However; even if such a tornado existed, it would be hard to identify even with an Enhanced Fujita scale. The damage would look mostly the same as an F5 tornado’s damage. It is thought that the more severe damage would be evidenced by specific funnel marks.
We have written many articles about the tornado for Universe Today. Here’s an article about how tornadoes are formed, and here are some pictures of tornado.
If you’d like more info on F6 tornadoes, check out amazing articles from:
Stormtrack.org
Tornado Project
We’ve also recorded an episode of Astronomy Cast all about planet Earth. Listen here, Episode 51: Earth.
[/caption]During the 19th century, one of the greatest discoveries in the history of physics was made by an Scottish physicist named James Clerk Maxwell. It was at this time, while studying the perplexing nature of magnetism and electricity, that he proposed a radical new theory. Electricity and magnetism, long thought to be separate forces, were in actuality closely associated with each other. That is, every electrical current has associated with it a magnetic field and every changing magnetic field creates its own electrical current. Maxwell went on to express this in a set of partial differential equations, known as Maxwell’s Equations, and form the basis for both electrical and Magnetic Energy.
In fact, thanks to Maxwell’s work, magnetic and electric energy are more appropriately considered as a single force. Together, they are what is known as electromagnetic energy – i.e. a form of energy that has both electrical and magnetic components. It is created when one runs a magnetic current through a wire or any other conducive material, creating a magnetic field. The magnetic energy generated can be used to attract other metal parts (as in the case in many modern machines that have moving parts) or can be used to generate electricity and store power (hydroelectric dams and batteries).
Since the 19th century, scientists have gone on to understand that many types of energy are in fact forms of electromagnetic energy. These include x rays, gamma rays, visible light (i.e. photons), ultraviolet light, infrared radiation, radio waves, and microwaves. These forms of electromagnetic energy differ from each other only in terms of the wavelength and frequency. Those forms which have shorter waves and higher frequencies tend to be the more harmful varieties, such as x-rays and gamma rays, while those that have longer waves and shorter frequencies, such as radio waves, tend to be more benign.
In mathematical terms, the equation for measuring the output of a magnetic field can be expressed as follows: V = L dI/dt + RI where V is volume, L is inductance, R is resistance, I is charge, dI represents change in charge, and dt represents change over time.
According to a new proposal, GPS satellites may be the key to finding dark matter. Credit: NASA
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In 1957, the Soviet Union launched the world’s first satellite, known as Sputnik. This changed the course of world history and led the United States, their chief rival in the Space Race, to mount a massive effort of its own to put manned craft in orbit and land a man on the moon. Since then, the presence of satellites in our atmosphere has become commonplace, which has muted the sense of awe and wonder involved. However, for many, especially students studying in engineering and aerospace programs, the question of How Satellites Work is still one of vital importance.
Satellite perform a wide array of functions. Some are observational, such as the Hubble Space Telescope – providing scientists with images of distant stars, nebulas, galaxies, and other deep space phenomena. Others are dedicated to scientific research, particularly the behavior of organisms in low-gravity environments. Then there are communications satellites which relay telecommunications signals back and forth across the globe. GPS satellites offer navigational aid and tracking aides to people looking to transport goods or navigate their way across land and oceans. And military satellites are used to observe and monitor enemy installations and formations on the ground while also helping the airforce and navy guide their ordinance to enemy targets.
Satellites are deployed by attaching them to rockets which then ferry them into orbit around the planet. Once deployed, they are typically powered by rechargeable batteries which are recharged through solar panels. Other satellites have internal fuel cells that convert chemical energy to electrical energy, while a few rely on nuclear power. Small thrusters provide attitude, altitude, and propulsion control to modify and stabilize the satellite’s position in space.
When it comes to classifying the orbit of a satellite, scientists use a varying list to describe the particular nature of their orbits. For example, Centric classifications refer to the object which the satellite orbits (i.e. planet Earth, the Moon, etc). Altitude classifications determine how far the satellite is from Earth, whether it is in low, medium or high orbit. Inclination refers to whether the satellite is in orbit around the equatorial plane, the polar regions, or the polar-sun orbit that passes the equator at the same local time on every pass so as to stay in the light. Eccentricity classifications describe whether the orbit is circular or elliptical, while Synchronous classifications describe whether or not the satellite’s rotation matches the rotational period of the object (i.e. a standard day).
Depending on the nature of their purpose, satellites also carry a wide range of components inside their housing. This can include radio equipment, storage containers, camera equipment, and even weaponry. In addition, satellites typically have an on-board computer to send and receive information from their controllers on the ground, as well as compute their positions and calculate course corrections.
