background preloader

Relativity of Electric and Magnetic Fields

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,

http://galileo.phys.virginia.edu/classes/252/rel_el_mag.html

Related:  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. Graphene High-quality graphene is strong, light, nearly transparent and an excellent conductor of heat and electricity. Its interactions with other materials and with light and its inherently two-dimensional nature produce unique properties, such as the bipolar transistor effect, ballistic transport of charges and large quantum oscillations. At the time of its isolation in 2004,[1] researchers studying carbon nanotubes were already familiar with graphene's composition, structure and properties, which had been calculated decades earlier. The combination of familiarity, extraordinary properties, surprising ease of isolation and unexpectedly high quality of the obtained graphene enabled a rapid increase in graphene research.

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." The 13 Most Important Numbers in the Universe - James D. Stein's Cosmic Numbers In the 17th century, scientists understood three phases of matter—solids, liquids and gases (the discovery of plasma, the fourth phase of matter, lay centuries in the future). Back then, solids and liquids were much harder to work with than gases because changes in solids and liquids were difficult to measure with the equipment of the time. So many experimentalists played around with gases to try to deduce fundamental physical laws. Robert Boyle was perhaps the first great experimentalist, and was responsible for what we now consider to be the essence of experimentation: vary one or more parameter, and see how other parameters change in response. It may seem obvious in retrospect, but hindsight, as the physicist Leo Szilard once remarked, is notably more accurate than foresight.

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.

Vertical Farms Sprout into Reality NEW YORK — Seven billion humans need farms that cover a land mass equal to South America, but tomorrow's farmers may need even more space to grow food for hungry mouths. Such urgency has given root to a new agricultural idea in the past few years — building vertical farms that climb toward the sky or burrow beneath the Earth. Vertical farming got a big boost from a class taught by Dickson Despommier, a microbiologist and ecologist at Columbia University, in 1999. The students' ideas spread virally across the Internet and led to the rise of the first modern vertical farms in the U.S., South Korea, Japan and Singapore. Sweden has plans for a vertical farm skyscraper reaching 17 stories in height.

Why Humans Prevailed NEW YORK — One hundred thousand years ago, several humanlike species walked the Earth. There were tribes of stocky Neanderthals eking out an existence in Europe and northwest Asia, and bands of cave-dwelling Denisovans in Asia. A diminutive, hobbitlike people called Homo floresiensis inhabited Indonesia. 7 Man-Made Substances that Laugh in the Face of Physics The universe is full of weird substances like liquid metal and whatever preservative keeps Larry King alive. But mankind isn't happy to accept the weirdness of nature when we can create our own abominations of science that, due to the miracle of technology, spit in nature's face and call it retarded. That's why we came up with... #7. Ferrofluids What do you get when you suspend nanoparticles of iron compounds in a colloidal solution of water, oil and a surfactant?

Secrets of the first practical artificial leaf A detailed description of development of the first practical artificial leaf -- a milestone in the drive for sustainable energy that mimics the process, photosynthesis, that green plants use to convert water and sunlight into energy -- appears in the ACS journal Accounts of Chemical Research. The article notes that unlike earlier devices, which used costly ingredients, the new device is made from inexpensive materials and employs low-cost engineering and manufacturing processes. Daniel G. Nocera points out that the artificial leaf responds to the vision of a famous Italian chemist who, in 1912, predicted that scientists one day would uncover the "guarded secret of plants." The most important of those, Nocera says, is the process that splits water into hydrogen and oxygen.

Giant Tropical Lake Found on Saturn Moon Titan An oasis of liquid methane has unexpectedly been discovered amid the tropical dunes of Saturn's moon Titan, researchers say. This lake in the otherwise dry tropics of Titan hints that subterranean channels of liquid methane might feed it from below, scientists added. Titan has clouds, rain and lakes, like Earth, but these are composed of methane rather than water. However, methane lakes were seen only at Titan's poles until now — its tropics around the equator were apparently home to dune fields instead.

Near-Space Tourism Balloon Runs Test Launch A new tourist experience could be provided within five years by a huge balloon that offers stunning views of the horizon and the blackness of space. The designer tested the launch procedure last month, using a smaller version of the helium balloon and its passenger pod. The May 29 test was halted when a wind gust damaged the balloon's envelope. Franken-Physics: Atoms Split in Two & Put Back Together Physicists have just upped their ante: Not only have they split atoms but, even trickier, they've put them back together. Their secret? Quantum physics. A team of scientists was able to "split" an atom into its two possible spin states, up and down, and measure the difference between them even after the atom resumed the properties of a single state. The research wasn't just playtime for quantum physicists: It could be a steppingstone toward the development of a quantum computer, a way to simulate quantum systems (as plant photosynthesis and other natural processes appear to be) that would help solve complex problems far more efficiently than present-day computers can.

Related: