1. Curent electric – An electric current is a flow of electric charge. In electric circuits this charge is carried by moving electrons in a wire. It can also be carried by ions in an electrolyte, or by both ions and electrons such as in an ionised gas. The SI unit for measuring a current is the ampere. Electric current is measured using a device called an ammeter, electric currents cause Joule heating, which creates light in incandescent light bulbs. They also create magnetic fields, which are used in motors, inductors and generators, the particles that carry the charge in an electric current are called charge carriers. In metals, one or more electrons from each atom are loosely bound to the atom and these conduction electrons are the charge carriers in metal conductors. The conventional symbol for current is I, which originates from the French phrase intensité de courant, current intensity is often referred to simply as current. The I symbol was used by André-Marie Ampère, after whom the unit of current is named, in formulating the eponymous Ampères force law. The notation travelled from France to Great Britain, where it became standard, in a conductive material, the moving charged particles which constitute the electric current are called charge carriers. In other materials, notably the semiconductors, the carriers can be positive or negative. Positive and negative charge carriers may even be present at the same time, a flow of positive charges gives the same electric current, and has the same effect in a circuit, as an equal flow of negative charges in the opposite direction. Since current can be the flow of positive or negative charges. The direction of current is arbitrarily defined as the same direction as positive charges flow. This is called the direction of current I. If the current flows in the direction, the variable I has a negative value. When analyzing electrical circuits, the direction of current through a specific circuit element is usually unknown. Consequently, the directions of currents are often assigned arbitrarilyCurent electric – A simple electric circuit, where current is represented by the letter i. The relationship between the voltage (V), resistance (R), and current (I) is V=IR; this is known as Ohm's Law.
2. Magnetosferă – A magnetosphere is the region of space surrounding an astronomical object in which charged particles are controlled by that objects magnetic field. The magnetic field near the surface of many astronomical objects resembles that of a dipole, the field lines farther away from the surface can be significantly distorted by the flow of electrically conducting plasma emitted from a nearby star. Study of Earths magnetosphere began in 1600, when William Gilbert discovered that the field on the surface of Earth resembled that on a terrella. In the 1940s, Walter M. Elsasser proposed the model of dynamo theory, through the use of magnetometers, scientists were able to study the variations in Earths magnetic field as functions of both time and latitude and longitude. Beginning in the late 1940s, rockets were used to study cosmic rays, in 1958, Explorer 1, the first of the Explorer series of space missions, was launched to study the intensity of cosmic rays above the atmosphere and measure the fluctuations in this activity. This mission observed the existence of the Van Allen radiation belt, also in 1958, Eugene Parker proposed the idea of the solar wind. The term magnetosphere was proposed by Thomas Gold in 1959, the Explorer 12 mission led to the observation by Cahill and Amazeen in 1963 of a sudden decrease in the strength of the magnetic field near the noon meridian, later named the magnetopause. In 1983, the International Cometary Explorer observed the magnetotail, or the distant magnetic field, the distance at which a planet can withstand the solar wind pressure is called the Chapman–Ferraro distance. Mercury, Earth, Jupiter, Ganymede, Saturn, Uranus, a magnetosphere is classified as induced when R C F ≪ R P, or when the solar wind is not opposed by the objects magnetic field. In this case, the solar wind interacts with the atmosphere or ionosphere of the planet, when R C F ≈ R P, the planet itself and its magnetic field both contribute. It is possible that Mars is of this type, the bow shock forms the outermost layer of the magnetosphere, the boundary between the magnetosphere and the ambient medium. For stars, this is usually the boundary between the wind and interstellar medium, for planets, the speed of the solar wind there decreases as it approaches the magnetopause. The magnetosheath is the region of the magnetosphere between the bow shock and the magnetopause and it is formed mainly from shocked solar wind, though it contains a small amount of plasma from the magnetosphere. It is an area exhibiting high particle flux, where the direction. This is caused by the collection of solar wind gas that has effectively undergone thermalization and it acts as a cushion that transmits the pressure from the flow of the solar wind and the barrier of the magnetic field from the object. The magnetopause is the area of the magnetosphere wherein the pressure from the magnetic field is balanced with the pressure from the solar wind. It is the convergence of the solar wind from the magnetosheath with the magnetic field of the object. Because both sides of this convergence contain magnetized plasma, the interactions between them are complex, the structure of the magnetopause depends upon the Mach number and beta of the plasma, as well as the magnetic fieldMagnetosferă – Infrared image and artist's concept of the bow shock around R Hydrae
3. Ionizare – Ionization is the process by which an atom or a molecule acquires a negative or positive charge by gaining or losing electrons to form ions, often in conjunction with other chemical changes. Ionization can result from the loss of an electron after collisions with particles, collisions with other atoms, molecules and ions. Heterolytic bond cleavage and heterolytic substitution reactions can result in the formation of ion pairs, ionization can occur through radioactive decay by the internal conversion process, in which an excited nucleus transfers its energy to one of the inner-shell electrons causing it to be ejected. Everyday examples of gas ionization are such as within a fluorescent lamp or other electrical discharge lamps and it is also used in radiation detectors such as the Geiger-Müller counter or the ionization chamber. The ionization process is used in a variety of equipment in fundamental science and in such as mass spectrometry. Negatively charged ions are produced when an electron collides with an atom and is subsequently trapped inside the electric potential barrier. The process is known as electron capture ionization, positively charged ions are produced by transferring a sufficient amount of energy to a bound electron in a collision with charged particles or with photons. The threshold amount of the energy is known as ionization potential. The study of such collisions is of importance with regard to the few-body problem. The Townsend discharge is an example of the creation of positive ions. It is a reaction involving electrons in a region with a sufficiently high electric field in a gaseous medium that can be ionized. Following an original event, due to such as ionizing radiation. If the electric field is strong enough, the free electron gains sufficient energy to liberate a further electron when it collides with another molecule. The two free electrons then travel towards the anode and gain sufficient energy from the field to cause impact ionization when the next collisions occur. This is effectively a chain reaction of electron generation, and is dependent on the free electrons gaining sufficient energy between collisions to sustain the avalanche, ionization efficiency is the ratio of the number of ions formed to the number of electrons or photons used. The trend in the energy of atoms is often used to demonstrate the periodic behavior of atoms with respect to the atomic number. This is a tool for establishing and understanding the ordering of electrons in atomic orbitals without going into the details of wave functions or the ionization process. An example is presented in figure 1, the periodic abrupt decrease in ionization potential after rare gas atoms, for instance, indicates the emergence of a new shell in alkali metalsIonizare – Figure 1. Ionization energies of neutral elements.
4. Centura de radiații Van Allen – A radiation belt is a zone of energetic charged particles, most of which originate from the solar wind that is captured by and held around a planet by that planets magnetic field. The Earth has two belts and sometimes others may be temporarily created. The discovery of the belts is credited to James Van Allen, Earths two main belts extend from an altitude of about 1,000 to 60,000 kilometers above the surface in which region radiation levels vary. Most of the particles form the belts are thought to come from solar wind. By trapping the solar wind, the magnetic field deflects those energetic particles, the belts are located in the inner region of the Earths magnetosphere. The belts trap energetic electrons and protons, other nuclei, such as alpha particles, are less prevalent. The belts endanger satellites, which must have their sensitive components protected with adequate shielding if they spend significant time in that zone, kristian Birkeland, Carl Størmer, and Nicholas Christofilos had investigated the possibility of trapped charged particles before the Space Age. Explorer 1 and Explorer 3 confirmed the existence of the belt in early 1958 under James Van Allen at the University of Iowa, the trapped radiation was first mapped by Explorer 4, Pioneer 3 and Luna 1. The term Van Allen belts refers specifically to the radiation belts surrounding Earth, however, the Sun does not support long-term radiation belts, as it lacks a stable, global, dipole field. The Earths atmosphere limits the belts particles to regions above 200–1,000 km, the belts are confined to a volume which extends about 65° on either side of the celestial equator. The NASA Van Allen Probes mission aims at understanding how populations of relativistic electrons and ions in space form or change in response to changes in solar activity, the Van Allen Probes mission successfully launched on August 30,2012. The primary mission is scheduled to last two years with expendables expected to last four, NASAs Goddard Space Flight Center manages the Living With a Star program of which the Van Allen Probes is a project, along with Solar Dynamics Observatory. The Applied Physics Laboratory is responsible for the implementation and instrument management for the Van Allen Probes, Radiation belts exist around other planets and moons in the solar system that have magnetic fields powerful enough to sustain them. To date, most of these belts have been poorly mapped. The Voyager Program only nominally confirmed the existence of similar belts around Uranus, the inner Van Allen Belt extends typically from an altitude of 0.2 to 2 Earth radii or 1,000 km to 6,000 km above the Earth. In certain cases when solar activity is stronger or in areas such as the South Atlantic Anomaly. The inner belt contains high concentrations of electrons in the range of hundreds of keV and energetic protons with energies exceeding 100 MeV, the source of lower energy protons is believed to be proton diffusion due to changes in the magnetic field during geomagnetic storms. Due to the offset of the belts from Earths geometric centerCentura de radiații Van Allen – Jupiter's variable radiation belts
5. Magnetohidrodinamică – Magnetohydrodynamics is the study of the magnetic properties of electrically conducting fluids. Examples of such magnetofluids include plasmas, liquid metals, salt water, the word magnetohydrodynamics is derived from magneto- meaning magnetic field, hydro- meaning water, and -dynamics meaning movement. The field of MHD was initiated by Hannes Alfvén, for which he received the Nobel Prize in Physics in 1970. The fundamental concept behind MHD is that magnetic fields can induce currents in a conductive fluid. The set of equations that describe MHD are a combination of the Navier-Stokes equations of fluid dynamics and these differential equations must be solved simultaneously, either analytically or numerically. The importance of the waves in this respect are pointed out. The ebbing salty water flowing past Londons Waterloo Bridge interacts with the Earths magnetic field to produce a difference between the two river-banks. Michael Faraday tried this experiment in 1832 but the current was too small to measure with the equipment at the time, however, by a similar process the voltage induced by the tide in the English Channel was measured in 1851. The simplest form of MHD, Ideal MHD, assumes that the fluid has so little resistivity that it can be treated as a perfect conductor and this is the limit of infinite magnetic Reynolds number. In ideal MHD, Lenzs law dictates that the fluid is in a sense tied to the field lines. To explain, in ideal MHD a small volume of fluid surrounding a field line will continue to lie along a magnetic field line. This is sometimes referred to as the field lines being frozen in the fluid. This difficulty in reconnecting magnetic field makes it possible to store energy by moving the fluid or the source of the magnetic field. The energy can become available if the conditions for ideal MHD break down. The ideal MHD equations consist of the continuity equation, the Cauchy momentum equation, Amperes Law neglecting displacement current, as with any fluid description to a kinetic system, a closure approximation must be applied to highest moment of the particle distribution equation. This is often accomplished with approximations to the flux through a condition of adiabaticity or isothermality. The main quantities which characterize the electrically conducting fluid are the plasma velocity field v, the current density J, the mass density ρ. The flowing electric charge in the plasma is the source of a magnetic field B, All quantities generally vary with time tMagnetohidrodinamică – The sun is an MHD system that is not well understood.
6. Curentul Birkeland – A Birkeland current is a set of currents that flow along geomagnetic field lines connecting the Earth’s magnetosphere to the Earths high latitude ionosphere. In the Earth’s magnetosphere, the currents are driven by the wind and interplanetary magnetic field. The strength of the Birkeland currents changes with activity in the magnetosphere, small scale variations in the upward current sheets accelerate magnetospheric electrons which, when they reach the upper atmosphere, create the Auroras Borealis and Australis. In the high latitude ionosphere, the Birkeland currents close through the region of the auroral electrojet, the Birkeland currents occur in two pairs of field-aligned current sheets. One pair extends from noon through the sector to the midnight sector. The other pair extends from noon through the sector to the midnight sector. The sheet on the high side of the auroral zone is referred to as the Region 1 current sheet. The currents were predicted in 1908 by Norwegian explorer and physicist Kristian Birkeland and this could only imply that currents were flowing in the atmosphere above. He theorized that somehow the Sun emitted a ray, and corpuscles from what is now known as a solar wind entered the Earth’s magnetic field and created currents. This view was scorned by other researchers, but in 1967 a satellite, launched into the auroral region, in honour of him and his theory these currents are named Birkeland currents. A good description of the discoveries by Birkeland is given in the book by Jago and these in turn lead to consequences such as acceleration of charged particles, both positive and negative, and element separation. Both of these classes of phenomena should have a general astrophysical interest far beyond that of understanding the environment of our own Earth. Auroral Birkeland currents carry about 100,000 amperes during quiet times, Birkeland had estimated currents at heights of several hundred kilometres, and strengths of up to a million amperes in 1908. The ionospheric currents that connect the field-aligned currents heat up the atmosphere due to the finite conductivity of the ionosphere. The heat is transferred from the plasma to the gas of the upper atmosphere. Birkeland currents can also be created in the laboratory with multi-terawatt pulsed power generators, the resulting cross-section pattern indicates a hollow beam of electrons in the form of a circle of vortices, a formation called the diocotron instability, that subsequently leads to filamentation. Such vortices can be seen in aurora as auroral curls, Birkeland currents are also one of a class of plasma phenomena called a z-pinch, so named because the azimuthal magnetic fields produced by the current pinches the current into a filamentary cable. This can also twist, producing a helical pinch that spirals like a twisted or braided rope, there is also a short-range circular component to the force between two Birkeland currents that is opposite to the longer-range parallel forcesCurentul Birkeland – Auroral-like Birkeland currents created by scientist Kristian Birkeland in his terrella, featuring a magnetised anode globe in an evacuated chamber.