Lightning is a violent and sudden electrostatic discharge where two electrically charged regions in the atmosphere temporarily equalize themselves during a thunderstorm. Lightning creates a wide range of electromagnetic radiations from the hot plasma created by the electron flow, including visible light in the form of black-body radiation. Thunder is the sound formed by the shock wave formed as gaseous molecules experience a rapid pressure increase; the three main kinds of lightning are: created either inside one thundercloud, or between two clouds, or between a cloud and the ground. The 15 recognized observational variants include "heat lightning", seen but not heard, dry lightning, which causes many forest fires, ball lightning, observed scientifically. Humans have deified lightning for millennia, lightning inspired expressions like "Bolt from the blue", "Lightning never strikes twice", "blitzkrieg" are common. In some languages, "Love at first sight" translates as "lightning strike"; the details of the charging process are still being studied by scientists, but there is general agreement on some of the basic concepts of thunderstorm electrification.
The main charging area in a thunderstorm occurs in the central part of the storm where air is moving upward and temperatures range from −15 to −25 °C, see figure to the right. At that place, the combination of temperature and rapid upward air movement produces a mixture of super-cooled cloud droplets, small ice crystals, graupel; the updraft carries the super-cooled cloud droplets and small ice crystals upward. At the same time, the graupel, larger and denser, tends to fall or be suspended in the rising air; the differences in the movement of the precipitation cause collisions to occur. When the rising ice crystals collide with graupel, the ice crystals become positively charged and the graupel becomes negatively charged. See figure to the left; the updraft carries. The larger and denser graupel is either suspended in the middle of the thunderstorm cloud or falls toward the lower part of the storm; the result is that the upper part of the thunderstorm cloud becomes positively charged while the middle to lower part of the thunderstorm cloud becomes negatively charged.
The upward motions within the storm and winds at higher levels in the atmosphere tend to cause the small ice crystals in the upper part of the thunderstorm cloud to spread out horizontally some distance from thunderstorm cloud base. This part of the thunderstorm cloud is called the anvil. While this is the main charging process for the thunderstorm cloud, some of these charges can be redistributed by air movements within the storm. In addition, there is a small but important positive charge buildup near the bottom of the thunderstorm cloud due to the precipitation and warmer temperatures. A typical cloud-to-ground lightning flash culminates in the formation of an electrically conducting plasma channel through the air in excess of 5 km tall, from within the cloud to the ground's surface; the actual discharge is the final stage of a complex process. At its peak, a typical thunderstorm produces three or more strikes to the Earth per minute. Lightning occurs when warm air is mixed with colder air masses, resulting in atmospheric disturbances necessary for polarizing the atmosphere.
However, it can occur during dust storms, forest fires, volcanic eruptions, in the cold of winter, where the lightning is known as thundersnow. Hurricanes generate some lightning in the rainbands as much as 160 km from the center; the science of lightning is called fulminology, the fear of lightning is called astraphobia. Lightning is not distributed evenly around the planet. On Earth, the lightning frequency is 44 times per second, or nearly 1.4 billion flashes per year and the average duration is 0.2 seconds made up from a number of much shorter flashes of around 60 to 70 microseconds. Many factors affect the frequency, distribution and physical properties of a typical lightning flash in a particular region of the world; these factors include ground elevation, prevailing wind currents, relative humidity, proximity to warm and cold bodies of water, etc. To a certain degree, the ratio between IC, CC and CG lightning may vary by season in middle latitudes; because human beings are terrestrial and most of their possessions are on the Earth where lightning can damage or destroy them, CG lightning is the most studied and best understood of the three types though IC and CC are more common types of lightning.
Lightning's relative unpredictability limits a complete explanation of how or why it occurs after hundreds of years of scientific investigation. About 70 % of lightning occurs over land in the tropics; this occurs from both the mixture of warmer and colder air masses, as well as differences in moisture concentrations, it happens at the boundaries between them. The flow of warm ocean currents past drier land masses, such as the Gulf Stream explains the elevated frequency of lightning in the Southeast United States; because the influence of small or absent land masses in the vast stretches of the world's oceans limits the differences between these variants in the atmosphere, lightning is notably less frequent there than over larger landforms. The North and South Poles are limited in their coverage of thunderstorms and theref
Earth's magnetic field
Earth's magnetic field known as the geomagnetic field, is the magnetic field that extends from the Earth's interior out into space, where it interacts with the solar wind, a stream of charged particles emanating from the Sun. The magnetic field, is generated by electric currents due to the motion of convection currents of molten iron in the Earth's outer core: these convection currents are caused by heat escaping from the core, a natural process called a geodynamo; the magnitude of the Earth's magnetic field at its surface ranges from 25 to 65 microteslas. As an approximation, it is represented by a field of a magnetic dipole tilted at an angle of about 11 degrees with respect to Earth's rotational axis, as if there were a bar magnet placed at that angle at the center of the Earth; the North geomagnetic pole located near Greenland in the northern hemisphere, is the south pole of the Earth's magnetic field, conversely. While the North and South magnetic poles are located near the geographic poles and continuously move over geological time scales, but sufficiently for ordinary compasses to remain useful for navigation.
However, at irregular intervals averaging several hundred thousand years, the Earth's field reverses and the North and South Magnetic Poles abruptly switch places. These reversals of the geomagnetic poles leave a record in rocks that are of value to paleomagnetists in calculating geomagnetic fields in the past; such information in turn is helpful in studying the motions of continents and ocean floors in the process of plate tectonics. The magnetosphere is the region above the ionosphere, defined by the extent of the Earth's magnetic field in space, it extends several tens of thousands of kilometers into space, protecting the Earth from the charged particles of the solar wind and cosmic rays that would otherwise strip away the upper atmosphere, including the ozone layer that protects the Earth from harmful ultraviolet radiation. The Earth's magnetic field serves to deflect most of the solar wind, whose charged particles would otherwise strip away the ozone layer that protects the Earth from harmful ultraviolet radiation.
One stripping mechanism is for gas to be caught in bubbles of magnetic field, which are ripped off by solar winds. Calculations of the loss of carbon dioxide from the atmosphere of Mars, resulting from scavenging of ions by the solar wind, indicate that the dissipation of the magnetic field of Mars caused a near total loss of its atmosphere; the study of past magnetic field of the Earth is known as paleomagnetism. The polarity of the Earth's magnetic field is recorded in igneous rocks, reversals of the field are thus detectable as "stripes" centered on mid-ocean ridges where the sea floor is spreading, while the stability of the geomagnetic poles between reversals has allowed paleomagnetists to track the past motion of continents. Reversals provide the basis for magnetostratigraphy, a way of dating rocks and sediments; the field magnetizes the crust, magnetic anomalies can be used to search for deposits of metal ores. Humans have used compasses for direction finding since the 11th century A.
D. and for navigation since the 12th century. Although the magnetic declination does shift with time, this wandering is slow enough that a simple compass remains useful for navigation. Using magnetoreception various other organisms, ranging from some types of bacteria to pigeons, use the Earth's magnetic field for orientation and navigation. At any location, the Earth's magnetic field can be represented by a three-dimensional vector. A typical procedure for measuring its direction is to use a compass to determine the direction of magnetic North, its angle relative to true North is the variation. Facing magnetic North, the angle the field makes with the horizontal is the inclination or magnetic dip; the intensity of the field is proportional to the force. Another common representation is in Y and Z coordinates; the intensity of the field is measured in gauss, but is reported in nanoteslas, with 1 G = 100,000 nT. A nanotesla is referred to as a gamma; the tesla is the SI unit of the magnetic field, B.
The Earth's field ranges between 25,000 and 65,000 nT. By comparison, a strong refrigerator magnet has a field of about 10,000,000 nanoteslas. A map of intensity contours is called an isodynamic chart; as the World Magnetic Model shows, the intensity tends to decrease from the poles to the equator. A minimum intensity occurs in the South Atlantic Anomaly over South America while there are maxima over northern Canada and the coast of Antarctica south of Australia; the inclination is given by an angle that can assume values between -90° to 90°. In the northern hemisphere, the field points downwards, it is straight down at the North Magnetic Pole and rotates upwards as the latitude decreases until it is horizontal at the magnetic equator. It continues to rotate upwards. Inclination can be measured with a dip circle. An isoclinic chart for the Earth's magnetic field is shown below. Declination is positive for an eastward deviation of the field relative to true north, it can be estimated by comparing the magnetic north/south heading on a compass with the direction of a celestial pole.
Maps include information on the declination as an angle or a small diagram showing the relationship between magnetic north and true north. Information on declination for a region can be represented by a chart with isogonic lines. Components of the Earth's
An electroscope is an early scientific instrument used to detect the presence of electric charge on a body. It detects; the amount of charge on an object is proportional to its voltage. The accumulation of enough charge to detect with an electroscope requires hundreds or thousands of volts, so electroscopes are used with high voltage sources such as static electricity and electrostatic machines. An electroscope can only give a rough indication of the quantity of charge; the electroscope was the first electrical measuring instrument. The first electroscope was a pivoted needle, invented by British physician William Gilbert around 1600; the pith-ball electroscope and the gold-leaf electroscope are two classical types of electroscope that are still used in physics education to demonstrate the principles of electrostatics. A type of electroscope is used in the quartz fiber radiation dosimeter. Electroscopes were used by the Austrian scientist Victor Hess in the discovery of cosmic rays. In 1731, Stephen Gray used a simple hanging thread, which would be attracted to any nearby charged object.
This was the first improvement on Gilbert's versorium from 1600. The pith-ball electroscope, invented by British schoolmaster and physicist John Canton in 1754, consists of one or two small balls of a lightweight nonconductive substance a spongy plant material called pith, suspended by silk or linen thread from the hook of an insulated stand. Tiberius Cavallo made an electroscope in 1770 with pith balls at the end of silver wires. Modern electroscopes use balls made of plastic. In order to test the presence of a charge on an object, the object is brought near to the uncharged pith ball. If the object is charged, the ball will move toward it; the attraction occurs because of induced polarization of the atoms inside the pith ball. All matter consists of electrically charged particles located close together; the pith is a nonconductor, so the electrons in the ball are bound to atoms of the pith and are not free to leave the atoms and move about in the ball, but they can move a little within the atoms.
See diagram at right. If, for example, a positively charged object is brought near the pith ball, the negative electrons in each atom will be attracted and move toward the side of the atom nearer the object; the positively charged nuclei will be repelled and will move away. Since the negative charges in the pith ball are now nearer the object than the positive charges, their attraction is greater than the repulsion of the positive charges, resulting in a net attractive force; this separation of charge is microscopic, but since there are so many atoms, the tiny forces add up to a large enough force to move a light pith ball. The pith ball can be charged by touching it to a charged object, so some of the charges on the surface of the charged object move to the surface of the ball; the ball can be used to distinguish the polarity of charge on other objects because it will be repelled by objects charged with the same polarity or sign it has, but attracted to charges of the opposite polarity. The electroscope will have a pair of suspended pith balls.
This allows one to tell at a glance. If one of the pith balls is touched to a charged object, charging it, the second one will be attracted and touch it, communicating some of the charge to the surface of the second ball. Now both balls have the same polarity charge, so they repel each other, they hang in an inverted'V' shape with the balls spread apart. The distance between the balls will give a rough idea of the magnitude of the charge; the gold-leaf electroscope was developed in 1787 by British clergyman and physicist Abraham Bennet, as a more sensitive instrument than pith ball or straw blade electroscopes in use. It consists of a vertical metal rod brass, from the end of which hang two parallel strips of thin flexible gold leaf. A disk or ball terminal is attached to the top of the rod. To protect the gold leaves from drafts of air they are enclosed in a glass bottle open at the bottom and mounted over a conductive base. There are grounded metal plates or foil strips in the bottle flanking the gold leaves on either side.
These are a safety measure. They capture charge leaking through the air that accumulate on the glass walls, that increase the sensitivity of the instrument. In the precision instruments the inside of the bottle was evacuated, to prevent the charge on the terminal from leaking off through the ionization of the air; when the metal terminal is touched with a charged object, the gold leaves spread apart in an inverted'V'. This is because some of the charge on the object is conducted through the terminal and metal rod to the leaves. Since they receive the same sign charge they repel each other and thus diverge. If the terminal is grounded by touching it with a finger, the charge is transferred through the human body into the earth and the gold leaves close together; the electroscope can be charged without touching it to a charged object, by electrostatic induction. If a charged object is brought near the electroscope terminal, the leaves diverge, because the electric field of the object causes charges in the electrosco
The electron is a subatomic particle, symbol e− or β−, whose electric charge is negative one elementary charge. Electrons belong to the first generation of the lepton particle family, are thought to be elementary particles because they have no known components or substructure; the electron has a mass, 1/1836 that of the proton. Quantum mechanical properties of the electron include an intrinsic angular momentum of a half-integer value, expressed in units of the reduced Planck constant, ħ; as it is a fermion, no two electrons can occupy the same quantum state, in accordance with the Pauli exclusion principle. Like all elementary particles, electrons exhibit properties of both particles and waves: they can collide with other particles and can be diffracted like light; the wave properties of electrons are easier to observe with experiments than those of other particles like neutrons and protons because electrons have a lower mass and hence a longer de Broglie wavelength for a given energy. Electrons play an essential role in numerous physical phenomena, such as electricity, magnetism and thermal conductivity, they participate in gravitational and weak interactions.
Since an electron has charge, it has a surrounding electric field, if that electron is moving relative to an observer, it will generate a magnetic field. Electromagnetic fields produced from other sources will affect the motion of an electron according to the Lorentz force law. Electrons absorb energy in the form of photons when they are accelerated. Laboratory instruments are capable of trapping individual electrons as well as electron plasma by the use of electromagnetic fields. Special telescopes can detect electron plasma in outer space. Electrons are involved in many applications such as electronics, cathode ray tubes, electron microscopes, radiation therapy, gaseous ionization detectors and particle accelerators. Interactions involving electrons with other subatomic particles are of interest in fields such as chemistry and nuclear physics; the Coulomb force interaction between the positive protons within atomic nuclei and the negative electrons without, allows the composition of the two known as atoms.
Ionization or differences in the proportions of negative electrons versus positive nuclei changes the binding energy of an atomic system. The exchange or sharing of the electrons between two or more atoms is the main cause of chemical bonding. In 1838, British natural philosopher Richard Laming first hypothesized the concept of an indivisible quantity of electric charge to explain the chemical properties of atoms. Irish physicist George Johnstone Stoney named this charge'electron' in 1891, J. J. Thomson and his team of British physicists identified it as a particle in 1897. Electrons can participate in nuclear reactions, such as nucleosynthesis in stars, where they are known as beta particles. Electrons can be created through beta decay of radioactive isotopes and in high-energy collisions, for instance when cosmic rays enter the atmosphere; the antiparticle of the electron is called the positron. When an electron collides with a positron, both particles can be annihilated, producing gamma ray photons.
The ancient Greeks noticed. Along with lightning, this phenomenon is one of humanity's earliest recorded experiences with electricity. In his 1600 treatise De Magnete, the English scientist William Gilbert coined the New Latin term electrica, to refer to those substances with property similar to that of amber which attract small objects after being rubbed. Both electric and electricity are derived from the Latin ēlectrum, which came from the Greek word for amber, ἤλεκτρον. In the early 1700s, Francis Hauksbee and French chemist Charles François du Fay independently discovered what they believed were two kinds of frictional electricity—one generated from rubbing glass, the other from rubbing resin. From this, du Fay theorized that electricity consists of two electrical fluids and resinous, that are separated by friction, that neutralize each other when combined. American scientist Ebenezer Kinnersley also independently reached the same conclusion. A decade Benjamin Franklin proposed that electricity was not from different types of electrical fluid, but a single electrical fluid showing an excess or deficit.
He gave them the modern charge nomenclature of negative respectively. Franklin thought of the charge carrier as being positive, but he did not identify which situation was a surplus of the charge carrier, which situation was a deficit. Between 1838 and 1851, British natural philosopher Richard Laming developed the idea that an atom is composed of a core of matter surrounded by subatomic particles that had unit electric charges. Beginning in 1846, German physicist William Weber theorized that electricity was composed of positively and negatively charged fluids, their interaction was governed by the inverse square law. After studying the phenomenon of electrolysis in 1874, Irish physicist George Johnstone Stoney suggested that there existed a "single definite quantity of electricity", the charge of a monovalent ion, he was able to estimate the value of this elementary charge e by means of Faraday's laws of electrolysis. However, Stoney could not be removed. In 1881, German physicist Hermann von Helmholtz argued that both positive and negative charges were divided into elementary parts, each of which "behaves like atoms of electricity".
Stoney coined the term
Aluminium or aluminum is a chemical element with symbol Al and atomic number 13. It is a silvery-white, soft and ductile metal in the boron group. By mass, aluminium makes up about 8% of the Earth's crust; the chief ore of aluminium is bauxite. Aluminium metal is so chemically reactive that native specimens are rare and limited to extreme reducing environments. Instead, it is found combined in over 270 different minerals. Aluminium is remarkable for its low density and its ability to resist corrosion through the phenomenon of passivation. Aluminium and its alloys are vital to the aerospace industry and important in transportation and building industries, such as building facades and window frames; the oxides and sulfates are the most useful compounds of aluminium. Despite its prevalence in the environment, no known form of life uses aluminium salts metabolically, but aluminium is well tolerated by plants and animals; because of these salts' abundance, the potential for a biological role for them is of continuing interest, studies continue.
Of aluminium isotopes, only 27Al is stable. This is consistent with aluminium having an odd atomic number, it is the only aluminium isotope that has existed on Earth in its current form since the creation of the planet. Nearly all the element on Earth is present as this isotope, which makes aluminium a mononuclidic element and means that its standard atomic weight equates to that of the isotope; the standard atomic weight of aluminium is low in comparison with many other metals, which has consequences for the element's properties. All other isotopes of aluminium are radioactive; the most stable of these is 26Al and therefore could not have survived since the formation of the planet. However, 26Al is produced from argon in the atmosphere by spallation caused by cosmic ray protons; the ratio of 26Al to 10Be has been used for radiodating of geological processes over 105 to 106 year time scales, in particular transport, sediment storage, burial times, erosion. Most meteorite scientists believe that the energy released by the decay of 26Al was responsible for the melting and differentiation of some asteroids after their formation 4.55 billion years ago.
The remaining isotopes of aluminium, with mass numbers ranging from 21 to 43, all have half-lives well under an hour. Three metastable states are known, all with half-lives under a minute. An aluminium atom has 13 electrons, arranged in an electron configuration of 3s23p1, with three electrons beyond a stable noble gas configuration. Accordingly, the combined first three ionization energies of aluminium are far lower than the fourth ionization energy alone. Aluminium can easily surrender its three outermost electrons in many chemical reactions; the electronegativity of aluminium is 1.61. A free aluminium atom has a radius of 143 pm. With the three outermost electrons removed, the radius shrinks to 39 pm for a 4-coordinated atom or 53.5 pm for a 6-coordinated atom. At standard temperature and pressure, aluminium atoms form a face-centered cubic crystal system bound by metallic bonding provided by atoms' outermost electrons; this crystal system is shared by some other metals, such as copper. Aluminium metal, when in quantity, is shiny and resembles silver because it preferentially absorbs far ultraviolet radiation while reflecting all visible light so it does not impart any color to reflected light, unlike the reflectance spectra of copper and gold.
Another important characteristic of aluminium is its low density, 2.70 g/cm3. Aluminium is a soft, lightweight and malleable with appearance ranging from silvery to dull gray, depending on the surface roughness, it is nonmagnetic and does not ignite. A fresh film of aluminium serves as a good reflector of visible light and an excellent reflector of medium and far infrared radiation; the yield strength of pure aluminium is 7–11 MPa, while aluminium alloys have yield strengths ranging from 200 MPa to 600 MPa. Aluminium has stiffness of steel, it is machined, cast and extruded. Aluminium atoms are arranged in a face-centered cubic structure. Aluminium has a stacking-fault energy of 200 mJ/m2. Aluminium is a good thermal and electrical conductor, having 59% the conductivity of copper, both thermal and electrical, while having only 30% of copper's density. Aluminium is capable of superconductivity, with a superconducting critical temperature of 1.2 kelvin and a critical magnetic field of about 100 gauss.
Aluminium is the most common material for the fabrication of superconducting qubits. Aluminium's corrosion resistance can be excellent due to a thin surface layer of aluminium oxide that forms when the bare metal is exposed to air preventing further oxidation, in a process termed passivation; the strongest aluminium alloys are less corrosion resistant due to galvanic reactions with alloyed copper. This corrosion resistance is reduced by aqueous salts in the presence of dissimilar metals. In acidic solutions, aluminium reacts with water to form hydrogen, in alkaline ones to form aluminates—protective passivation under these conditions is negligible; because it is corroded by dissolved chlorides, such as common sodium chloride, household plumbing is never made from aluminium. However, because
Electrostatic induction known as "electrostatic influence" or "influence" in Europe and Latin America, is a redistribution of electric charge in an object, caused by the influence of nearby charges. In the presence of a charged body, an insulated conductor develops a positive charge on one end and a negative charge on the other end. Induction was discovered by British scientist John Canton in 1753 and Swedish professor Johan Carl Wilcke in 1762. Electrostatic generators, such as the Wimshurst machine, the Van de Graaff generator and the electrophorus, use this principle. Due to induction, the electrostatic potential is constant at any point throughout a conductor. Electrostatic Induction is responsible for the attraction of light nonconductive objects, such as balloons, paper or styrofoam scraps, to static electric charges. Electrostatic induction laws apply in dynamic situations as far as the quasistatic approximation is valid. Electrostatic induction should not be confused with Electromagnetic induction.
A normal uncharged piece of matter has equal numbers of positive and negative electric charges in each part of it, located close together, so no part of it has a net electric charge. The positive charges are the atoms' nuclei which are bound into the structure of matter and are not free to move; the negative charges are the atoms' electrons. In electrically conductive objects such as metals, some of the electrons are able to move about in the object; when a charged object is brought near an uncharged, electrically conducting object, such as a piece of metal, the force of the nearby charge due to Coulomb's law causes a separation of these internal charges. For example, if a positive charge is brought near the object, the electrons in the metal will be attracted toward it and move to the side of the object facing it; when the electrons move out of an area, they leave an unbalanced positive charge due to the nuclei. This results in a region of negative charge on the object nearest to the external charge, a region of positive charge on the part away from it.
These are called induced charges. If the external charge is negative, the polarity of the charged regions will be reversed. Since this process is just a redistribution of the charges that were in the object, it doesn't change the total charge on the object; this induction effect is reversible. However, the induction effect can be used to put a net charge on an object. If, while it is close to the positive charge, the above object is momentarily connected through a conductive path to electrical ground, a large reservoir of both positive and negative charges, some of the negative charges in the ground will flow into the object, under the attraction of the nearby positive charge; when the contact with ground is broken, the object is left with a net negative charge. This method can be demonstrated using a gold-leaf electroscope, an instrument for detecting electric charge; the electroscope is first discharged, a charged object is brought close to the instrument's top terminal. Induction causes a separation of the charges inside the electroscope's metal rod, so that the top terminal gains a net charge of opposite polarity to that of the object, while the gold leaves gain a charge of the same polarity.
Since both leaves have the same charge, they spread apart. The electroscope has not acquired a net charge: the charge within it has been redistributed, so if the charged object were to be moved away from the electroscope the leaves will come together again, but if an electrical contact is now made between the electroscope terminal and ground, for example by touching the terminal with a finger, this causes charge to flow from ground to the terminal, attracted by the charge on the object close to the terminal. This charge neutralizes the charge in the gold leaves, so the leaves come together again; the electroscope now contains a net charge opposite in polarity to that of the charged object. When the electrical contact to earth is broken, e.g. by lifting the finger, the extra charge that has just flowed into the electroscope cannot escape, the instrument retains a net charge. The charge is held in the top of the electroscope terminal by the attraction of the inducing charge, but when the inducing charge is moved away, the charge is released and spreads throughout the electroscope terminal to the leaves, so the gold leaves move apart again.
The sign of the charge left on the electroscope after grounding is always opposite in sign to the external inducing charge. The two rules of induction are: If the object is not grounded, the nearby charge will induce equal and opposite charges in the object. If any part of the object is momentarily grounded while the inducing charge is near, a charge opposite in polarity to the inducing charge will be attracted from ground into the object, it will be left with a charge opposite to the inducing charge. A remaining question is; the movement of charges is caused by the force exerted on them by the electric field of the external charged object, by Coulomb's law. As the charges in the metal object continue to separate, the resulting positive and negative regions create their own electric field, which opposes the field of the external charge; this process continues until quickly an equilibrium is reached in which the induced charges are the right size to cancel the external electric field throughout the interior of the metal object.
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