# Relativity of Electric and Magnetic Fields

previous home next PDF Michael Fowler, University of Virginia A Magnetic Puzzle… Suppose we have an infinitely long straight wire, having a charge density of electrons of –λ coulombs per meter, all moving at speed v to the right (recall typical speeds are centimeters per minute) and a neutralizing fixed background of positive charge, also of course λ coulombs per meter. The current in the wire has magnitude I = λv (and actually is flowing to the left, since the moving electrons carry negative charge). Suppose also that a positive charge q is outside the wire, a distance r from the axis, and this outside charge is moving at the same exact velocity as the electrons in the wire. What force does the positive charge q feel? The wire is electrically neutral, since it contains equal densities of positive and negative charges, both uniformly distributed throughout the wire (the illustration above is of course schematic). However, since q is moving, it will feel a magnetic force, Related:  Magnetism

Japanese breakthrough will make wind power cheaper than nuclear NOTE: Some major wind projects like the proposed TWE Carbon Valley project in Wyoming are already pricing in significantly lower than coal power -- \$80 per MWh for wind versus \$90 per MWh for coal -- and that is without government subsidies using today's wind turbine technology. The International Clean Energy Analysis (ICEA) gateway estimates that the U.S. possesses 2.2 million km2 of high wind potential (Class 3-7 winds) — about 850,000 square miles of land that could yield high levels of wind energy. This makes the U.S. something of a Saudi Arabia for wind energy, ranked third in the world for total wind energy potential. The United States uses about 26.6 billion MWh's, so at the above rate we could satisfy a full one-third of our total annual energy needs. Now what if a breakthrough came along that potentially tripled the energy output of those turbines? You see where I'm going. Well, such a breakthrough has been made, and it's called the "wind lens." Editor's note: Want more info?

What is Magnetism? | Magnetic Fields & Magnetic Force Magnetism is one aspect of the combined electromagnetic force. It refers to physical phenomena arising from the force caused by magnets, objects that produce fields that attract or repel other objects. A magnetic field exerts a force on particles in the field due to the Lorentz force, according to Georgia State University's HyperPhysics website. The motion of electrically charged particles gives rise to magnetism. All materials experience magnetism, some more strongly than others. How the King of Snakes Makes a Meal Out of Rival Serpents | Video The kingsnake triumphs over larger, rival serpents by squeezing them to death with its powerful constriction. Magnetic fields are generated by rotating electric charges, according to HyperPhysics. Magnetic field sources are dipolar, having a north and south magnetic pole. The Earth itself is a giant magnet. Other metals besides iron have been found to have ferromagnetic properties. The applications of electromagnets are nearly countless.

The Borg of the Microbes Takes Up . . . Farming? You are witnessing one of nature's most incredible migrations that never gets shown on the Discovery Channel. Believe it or not, each one of those little dots is a solitary amoeba. But not for long. Note: This post contains a prize inside! It will await those patient enough to dig to the bottom. : ) Regular readers of this blog know well about my weakness for the protists formerly known as slime molds (scientists know apparently prefer the more PC and sexy “social amoebae”, although how you can get much sexier than “slime mold” I really don’t know). Before we get into their new status as potential FFA members, let’s talk a little bit about this particular group of slimes. But there is another kind of slime mold. In a cellular slime mold, something even more remarkable happens: a single amoeba called a myxamoeba suddenly decides it is starving. Take a look at this process: That aggregation star at left is a schematic of what you're seeing in the image at the top of this page. Yes.

people Perpetual Futility A short history of the search for perpetual motion. by Donald E. Simanek Popular histories too often present perpetual motion machines as "freaks and curiosities" of engineering without telling us just how they were understood at the time. Sometimes a particular device comes to us with a label, such as "Bishop Wilkins' magnetic perpetual motion machine." Bhaskara's Wheels. Villard de Honnecourt was born in the late 12th century and probably lived and worked in the north of France from 1225 to 1250. The most celebrated of his machine designs was for a perpetual motion wheel. Many a time have skilful workmen tried to contrive a wheel that should turn of itself; here is a way to make such a one, by means of an uneven number of mallets, or by quicksilver (mercury). The reference to quicksilver (mercury) indicates that Villard was familiar with the Bhaskara device, whose design had reached Europe. Mariano di Iacopo, called Taccola (Siena, 1382-1458?) 56. That's it.

arXiv.org e-Print archive Interplanetary Transport Network Not to be confused with InterPlanetary Network This stylized depiction of the ITN is designed to show its (often convoluted) path through the Solar System. The green ribbon represents one path from among the many that are mathematically possible along the surface of the darker green bounding tube. Locations where the ribbon changes direction abruptly represent trajectory changes at Lagrange points, while constricted areas represent locations where objects linger in temporary orbit around a point before continuing on. The Interplanetary Transport Network (ITN)[1] is a collection of gravitationally determined pathways through the Solar System that require very little energy for an object to follow. The ITN makes particular use of Lagrange points as locations where trajectories through space are redirected using little or no energy. History As it turns out, it is very easy to transit from a path leading to the point to one leading back out. Further explanation See also

Lévitation Magnétique For years, NASA has been researching the possibility of using the high speeds of maglev transportation to fling spacecraft into low Earth orbit. "It would really open up space to human exploration and commercialization," Powell says. "It's something we can't do now because it's too expensive." Powell and his colleagues have proposed two generations of space launching technology. And that's just the first generation.

Electric fish diverging Carl Hopkins Although these fish look alike and have the same DNA genetic makeup, they have very different electrical signals and will only mate with fish that produce the same signals. Cornell researchers believe that these different electrical signals are the fishes' first step in diverging into separate species. Avoiding quicksand along the banks of the Ivindo River in Gabon, Cornell neurobiologists armed with oscilloscopes search for shapes and patterns of electricity created by fish in the water. They know from their previous research that the various groups of local electric fish have different DNA, different communication patterns and won't mate with each other. The researchers' conclusion: The fish appear to be on the verge of forming two separate species. The electric fish -- known as mormyrids -- emit weak electric fields from a batterylike organ in their tails to sense their surroundings and communicate with other fish. Except for some, Arnegard has discovered.

MAKE HOMEMADE SCIENCE TOYS AND PROJECTS Space Settlement - National Space Society We Can Do It When the first person landed on the Moon in 1969 after only eight short years of intense effort, the National Aeronautics and Space Administration (NASA) proved that we could do nearly anything we put our minds and resources to that is consistent with understood principles of engineering and science. A few years later, Princeton physicist Gerard O'Neill and others showed that large orbital space settlements would fall within understood principles of engineering and science [Refs. 1-5]. Dr. O'Neill's analysis strongly suggested that asteroids and lunar mines could supply the materials, the Sun could provide the energy, and that our technology had nearly reached the point where we could build space settlements. In 1990, Robert Zubrin and David Baker described a program called Mars Direct, an innovative approach to beginning the settlement of Mars. Many plans for space settlement have been proposed — in orbit, on the Moon, on Mars, the asteroids, or elsewhere. A Better Future

Magnetism A magnetic quadrupole Magnetism is a class of physical phenomena that includes forces exerted by magnets on other magnets. It has its origin in electric currents and the fundamental magnetic moments of elementary particles. These give rise to a magnetic field that acts on other currents and moments. All materials are influenced to some extent by a magnetic field. The strongest effect is on permanent magnets, which have persistent magnetic moments caused by ferromagnetism. The magnetic state (or phase) of a material depends on temperature (and other variables such as pressure and the applied magnetic field) so that a material may exhibit more than one form of magnetism depending on its temperature, etc. History In ancient China, the earliest literary reference to magnetism lies in a 4th-century BC book named after its author, The Master of Demon Valley (鬼谷子): "The lodestone makes iron come or it attracts it Michael Faraday, 1842 Sources of magnetism Topics Diamagnetism

Hot springs microbe yields record-breaking, heat-tolerant enzyme Bioprospectors from the University of California, Berkeley, and the University of Maryland School of Medicine have found a microbe in a Nevada hot spring that happily eats plant material – cellulose – at temperatures near the boiling point of water. In fact, the microbe’s cellulose-digesting enzyme, called a cellulase, is most active at a record 109 degrees Celsius (228 degrees Fahrenheit), significantly above the 100℃ (212℉) boiling point of water. A 94°C geothermal pool, with a level-maintaining siphon, near Gerlach, Nevada. This so-called hyperthermophilic microbe, discovered in a 95℃ (203℉) geothermal pool, is only the second member of the ancient group Archaea known to grow by digesting cellulose above 80℃. “These are the most thermophilic Archaea discovered that will grow on cellulose and the most thermophilic cellulase in any organism,” said coauthor Douglas S. Clark and coworkers at UC Berkeley are teaming with colleagues, led by Frank T. For more information:

Related:  physics