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Charged Particle

Charged particle

In physics, a charged particle is a particle with an electric charge. It may be either a subatomic particle or an ion. A collection of charged particles, or even a gas containing a proportion of charged particles, is called a plasma, which is called the fourth state of matter because its properties are quite different from solids, liquids and gases. Category:Electromagnetism



Electric charge

Electric charge is a fundamental conserved property of some subatomic particles, which determines their electromagnetic interactions. Electrically charged matter is influenced by, and produces, electromagnetic fields. The interaction between charge and field is the source of one of the four fundamental forces, the electromagnetic force.

Overview

Electric charge is a characteristic of subatomic particles, and is quantized. For example, electrons have a charge, by convention, of −1. Protons have the opposite charge of +1. Quarks have a fractional charge of −1/3 or +2/3. The antiparticle equivalents of these have the opposite charge. There are other charged particles. The SI unit of electric charge is the coulomb, which represents approximately 6.24 x 1018 elementary charges (the charge on a single electron or proton). The coulomb is defined as the quantity of charge that has passed through the cross-section of a conductor carrying one ampere within one second. The symbol Q is used to denote a quantity of electric charge. Electric charge can be directly measured with an electrometer. The discrete nature of electric charge was demonstrated by Robert Millikan in his oil-drop experiment. Formally, a measure of charge should be a multiple of the elementary charge e (charge is quantized), but since it is an average, macroscopic quantity, many orders of magnitude larger than a single elementary charge, it can effectively take on any real value.

History

As reported by the Ancient Greek philosopher Thales of Miletus around 600 BC, charge (or electricity) could be accumulated by rubbing fur on various substances, such as amber. The Greeks noted that the charged amber buttons could attract light objects such as hair. They also noted that if they rubbed the amber for long enough, they could even get a spark to jump. This property derives from the triboelectric effect. The word electricity derives from ηλεκτρον (electron), the Greek word for amber. C. F. Du Fay proposed in 1733 [http://www.sparkmuseum.com/BOOK_DUFAY.HTM] that electricity came in two varieties which cancelled each other, and expressed this in terms of a two-fluid theory. When glass was rubbed with silk, DuFay said that the glass was charged with vitreous electricity, and when amber was rubbed with fur, the amber was said to be charged with resinous electricity. By the 18th century, the study of electricity had become popular. One of the foremost experts was Benjamin Franklin, who argued in favor of a one-fluid theory of electricity. Franklin imagined electricity as being a type of invisible fluid present in all matter; for example he believed that it was the glass in a Leyden jar that held the accumulated charge. He posited that rubbing insulating surfaces together caused this fluid to change location, and that a flow of this fluid constitutes an electric current. He also posited that when matter contained too little of the fluid it was "negatively" charged, and when it had an excess it was "positively" charged. Arbitrarily (or for a reason that was not recorded) he identified the term "positive" with vitreous electricity and "negative" with resinous electricity. William Watson arrived at the same explanation at about the same time. We now know that the Franklin/Watson model was close, but too simple. Matter is actually composed of several kinds of electrically charged particles, the most common being the positively charged proton and the negatively charged electron. Rather than one possible electric current there are many: a flow of electrons, a flow of electron "holes" which act like positive particles, or in electrolytic solutions, a flow of both negative and positive particles called ions moving in opposite directions. To reduce this complexity, electrical workers still use Franklin's convention and they imagine that electric current (known as conventional current) is a flow of exclusively positive particles. The conventional current simplifies electrical concepts and calculations, but it ignores the fact that within some conductors (electrolytes, semiconductors, and plasma), two or more species of electric charges flow in opposite directions. The flow direction for conventional current is also backwards compared to the actual electron drift taking place during electric currents in metals, the typical conductor of electricity, which is a source of confusion for beginners in electronics.

Properties

Aside from the properties described in articles about electromagnetism, charge is a relativistic invariant. This means that any particle that has charge q, no matter how fast it goes, always has charge q. This property has been experimentally verified by showing that the charge of one helium nucleus (two protons and two neutrons bound together in a nucleus and moving around at incredible speeds) is the same as two deuterium nuclei (one proton and one neutron bound together, but moving much more slowly than they would if they were in a helium nucleus).

Conservation of charge

The total electric charge of isolated systems remains constant regardless of changes within the system itself. This law is inherent to all processes known to physics and can be derived in a local form from Maxwell's equation as a continuity equation. More generally, the net change in charge density \rho within a volume of integration V is equal to the area integral over the current density J on the surface of the volume S, which is in turn equal to the net current I: :- \frac \int_V \rho dV = \int_S \mathbf \cdot \mathbf = I

See also


- Charge decay
- Current density
- Electrical discharge
- SI electromagnetism units

External links


- [http://www.unitconversion.org/unit_converter/charge.html Online Charge Converter] - convert between various units of charge, such as coulomb, EMU of charge, franklin, ampere-hour, faraday, and so on
- [http://www.unitconversion.org/unit_converter/charge-v.html Interactive Charge Conversion Table] - convert selected unit to all other units of charge
- [http://www.ce-mag.com/archive/2000/marapril/mrstatic.html How fast does a charge decay?]
- Category:Electricity Category:Physical quantity Category:Chemical properties Category:Introductory physics Category:Fundamental physics concepts ko:전하 ja:電荷

Ion

: This article is about the electrically charged particle. For other uses of this word, see ion (disambiguation). An ion is an atom or group of atoms with a net electric charge. A negatively charged ion, which has more electrons in its electron shell than it has protons in its nucleus, is known as an anion, for it is attracted to anodes, and a positively charged ion, which has fewer electrons than protons, is known as a cation (pronounced cat-eye-on), for it is attracted to cathodes. The process of converting into ions and the state of being ionized is called ionization. The recombining of ions and electrons to form neutral atoms is called recombination. Polyatomic anions which contain oxygen are sometimes known as oxyanion. Atomic and polyatomic ions are denoted by a superscript with the sign of the net electric charge and the number of electrons lost or gained, if more than one. For example: H+, SO32−. A collection of non-aqueous ions, or even a gas containing a proportion of charged particles, is called a plasma, which is called the fourth state of matter because its properties are quite different from solids, liquids, and gases.

Ionization potential

The energy required to detach an electron in its lowest energy state from an atom or molecule of a gas with less net electric charge is called the ionization potential, or ionization energy. The nth ionization energy of an atom is the energy required to detach its nth electron after the first n − 1 electrons have already been detached. Each successive ionization energy is markedly greater than the last. Particularly great increases occur after any given block of atomic orbitals is exhausted of electrons. For this reason, ions tend to form in ways that leave them with full orbital blocks. For example, sodium has one valence electron, in its outermost shell, so in ionized form it is commonly found with one lost electron, as Na+. On the other side of the periodic table, chlorine has seven valence electrons, so in ionized form it is commonly found with one gained electron, as Cl−. Francium has the lowest ionization energy of all the elements and fluorine has the greatest.

Other ions

A dianion is a species which has two negative charges on it. For example, the dianion of pentalene is aromatic. A zwitterion is an ion with a net charge of zero, but has both a positive and negative charge on it.

History

Ions were first theorized by Michael Faraday around 1830, to describe the portions of molecules that travel either to an anode or to a cathode. However, the mechanism by which this was achieved was not described until 1884 by Svante August Arrhenius in his doctoral dissertation to the University of Uppsala. His theory was initially not accepted but his dissertation won the Nobel Prize in Chemistry in 1903.

Etymology

The word ion is a name given by Michael Faraday, from Greek , neutral present participle of , "to go", thus "a goer". So, anion, , and cation, κ, mean "(a thing) going up" and "(a thing) going down", respectively, and anode, , and cathode, κ, mean "a going up" and "a going down", respectively, from , "way".

Applications

Ions are essential to life. Sodium, potassium, calcium and other ions play an important role in the cells of living organisms, particularly in cell membranes. They have many practical, everyday applications in items such as smoke detectors and are also finding use in unconventional technologies such as ion engines and ion cannons. Category:Physical chemistry ko:이온 ms:Ion ja:イオン simple:Ion th:ไอออน

Plasma

:This article is about plasma in the sense of an ionized gas. For other uses of the term, such as blood plasma, see plasma (disambiguation). plasma (disambiguation) In physics and chemistry, a plasma is an ionized gas, and is usually considered to be a distinct phase of matter. "Ionized" in this case means that at least one electron has been removed from a significant fraction of the molecules. The free electric charges make the plasma electrically conductive so that it couples strongly to electromagnetic fields. This fourth state of matter was first identified by Sir William Crookes in 1879 and dubbed "plasma" by Irving Langmuir in 1928, because it reminded him of a blood plasma [http://www.plasmacoalition.org/what.htm].

Common plasmas

blood plasma Plasmas are the most common phase of matter. The entire visible universe outside the Solar System is plasma, since all we can see are stars. Since the space between the stars is filled with a plasma, although a very sparse one (see interstellar- and intergalactic medium), essentially the entire volume of the universe is plasma. In the Solar System, the planet Jupiter accounts for most of the non-plasma, only about 0.1% of the mass and 10−15 of the volume within the orbit of Pluto. Alfvén also noted that due to their electric charge, very small grains also behave as ions and form part of a plasma (see dusty plasmas). Commonly encountered forms of plasma include:
- Artificially produced
  - Inside fluorescent lamps (low energy lighting), neon signs
  - Rocket exhaust
  - The area in front of a spacecraft's heat shield during reentry into the atmosphere
  - Fusion energy research
  - The electric arc in an arc lamp or an arc welder
  - Plasma ball (sometimes called a plasma sphere or plasma globe)
- Earth plasmas
  - Flames (ie. fire)
  - Lightning
  - The ionosphere
  - The polar aurorae
- Space and astrophysical
  - The Sun and other stars (which are plasmas heated by nuclear fusion)
  - The solar wind
  - The Interplanetary medium (the space between the planets)
  - The Interstellar medium (the space between star systems)
  - The Intergalactic medium (the space between galaxies)
  - The Io-Jupiter flux-tube
  - Accretion disks
  - Interstellar nebulae

Characteristics

The term plasma is generally reserved for a system of charged particles large enough to behave as one. Even a partially ionized gas in which as little as 1% of the particles are ionized can have the characteristics of a plasma (i.e. respond to magnetic fields and be highly electrically conductive). In technical terms, the typical characteristics of a plasma are: # Debye screening lengths that are short compared to the physical size of the plasma. # Large number of particles within a sphere with a radius of the Debye length. # Mean time between collisions usually is long when compared to the period of plasma oscillations.

Plasma scaling

Plasmas and their characteristics exist over a wide range of scales (ie. they are scaleable over many orders of magnitude). The following chart deals only with conventional atomic plasmas and not other exotic phenomena, such as, quark gluon plasmas:
Typical plasma scaling ranges: orders of magnitude (OOM)
CharacteristicTerrestrial plasmasCosmic plasmas
Size
in metres (m)		10−6 m (lab plasmas) to:
102 m (lightning) (~8 OOM)		10−6 m (spacecraft sheath) to
1025 m (intergalactic nebula) (~31 OOM)
Lifetime
in seconds (s)		10−12 s (laser-produced plasma) to:
107 s (fluorescent lights) (~19 OOM)		101 s (solar flares) to:
1017 s (intergalactic plasma) (~17 OOM)
Density
in particles per
cubic metre		107 to:
1021 (inertial confinement plasma)		1030 (stellar core) to:
100 (i.e., 1) (intergalactic medium)
Temperature
in kelvins (K)		~0 K (Crystalline non-neutral plasma[http://sdphca.ucsd.edu/]) to:
108 K (magnetic fusion plasma)		102 K (aurora) to:
107 K (Solar core)
Magnetic fields
in teslas (T)		10−4 T (Lab plasma) to:
103 T (pulsed-power plasma)		10−12 T (intergalactic medium) to:
107 T (Solar core)

Temperatures

plasma scaling characteristic of the gas being excited.]] The defining characteristic of a plasma is ionization. Although ionization can be caused by UV radiation, energetic particles, or strong electric fields, (processes that tend to result in a non-Maxwellian electron distribution function), it is more commonly caused by heating the electrons in such a way that they are close to thermal equilibrium so the electron temperature is relatively well-defined. Because the large mass of the ions relative to the electrons hinders energy transfer, it is possible for the ion temperature to be very different from (usually lower than) the electron temperature. The degree of ionization is determined by the electron temperature relative to the ionization energy (and more weakly by the density) in accordance with the Saha equation. If only a small fraction of the gas molecules are ionized (for example 1%), then the plasma is said to be a cold plasma, even though the electron temperature is typically several thousand degrees. The ion temperature in a cold plasma is often near the ambient temperature. Because the plasmas utilized in plasma technology are typically cold, they are sometimes called technological plasmas. They are often created by using a very high electric field to accelerate electrons, which then ionize the atoms. The electric field is either capacitively or inductively coupled into the gas by means of a plasma source, e.g. microwaves. Common applications of cold plasmas include plasma-enhanced chemical vapor deposition, plasma ion doping, and reactive ion etching. A hot plasma, on the other hand, is nearly fully ionized. This is what would commonly be known as the "fourth-state of matter". The Sun is an example of a hot plasma. The electrons and ions are more likely to have equal temperatures in a hot plasma, but there can still be significant differences.

Densities

Next to the temperature, which is of fundamental importance for the very existence of a plasma, the most important property is the density. The word "plasma density" by itself usually refers to the electron density, that is, the number of free electrons per unit volume. The ion density is related to this by the average charge state \langle Z\rangle of the ions through n_e=\langle Z\rangle n_i. (See quasineutrality below.) The third important quantity is the density of neutrals n_0. In a hot plasma this is small, but may still determine important physics. The degree of ionization is n_i/(n_0+n_i).

Potentials

reactive ion etching Since plasmas are very good conductors, electric potentials play an important role. The potential as it exists on average in the space between charged particles, independent of the question of how it can be measured, is called the plasma potential or the space potential. If an electrode is inserted into a plasma, its potential will generally lie considerably below the plasma potential due to the development of a Debye sheath. Due to the good electrical conductivity, the electric fields in plasmas tend to be very small, although where double layers are formed, the potential drop can be large enough to accelerate ions to relativistic velocities and produce synchrotron radiation such as x-rays and gamma rays. This results in the important concept of quasineutrality, which says that, on the one hand, it is a very good approximation to assume that the density of negative charges is equal to the density of positive charges (n_e=\langle Z\rangle n_i), but that, on the other hand, electric fields can be assumed to exist as needed for the physics at hand. The magnitude of the potentials and electric fields must be determined by means other than simply finding the net charge density. A common example is to assume that the electrons satisfy the Boltzmann relation, n_e \propto e^. Differentiating this relation provides a means to calculate the electric field from the density: \vec = (k_BT_e/e)(\nabla n_e/n_e). It is, of course, possible to produce a plasma that is not quasineutral. An electron beam, for example, has only negative charges. The density of a non-neutral plasma must generally be very low, or it must be very small, otherwise it will be dissipated by the repulsive electrostatic force. In astrophysical plasmas, Debye screening prevents electric fields from directly affecting the plasma over large distances (ie. greater than the Debye length). But the existence of charged particles causes the plasma to generate and be affected by magnetic fields. This can and does cause extremely complex behavior, such as the generation of plasma double layers, an object that separates charge over a few tens of Debye lengths. The dynamics of plasmas interacting with external and self-generated magnetic fields are studied in the academic discipline of magnetohydrodynamics.

In contrast to the gas phase

Plasma is often called the fourth state of matter. It is distinct from the three lower-energy phases of matter; solid, liquid, and gas, although it is closely related to the gas phase in that it also has no definite form or volume. There is still some disagreement as to whether a plasma is a distinct state of matter or simply a type of gas. Most physicists consider a plasma to be more than a gas because of a number of distinct properties including the following:
Property Gas Plasma
Electrical Conductivity Very low
 		 Very high
  1. For many purposes the electric field in a plasma may be treated as zero, although when current flows the voltage drop, though small, is finite, and density gradients are usually associated with an electric field according to the Boltzmann relation.
  2. The possibility of currents couples the plasma strongly to magnetic fields, which are responsible for a large variety of structures such as filaments, sheets, and jets.
  3. Collective phenomena are common because the electric and magnetic forces are both long-range and potentially many orders of magnitude stronger than gravitational forces.
Independently acting species One Two or three
Electrons, ions, and neutrals can be distinguished by the sign of their charge so that they behave independently in many circumstances, having different velocities or even different temperatures, leading to new types of waves and instabilities, among other things
Velocity distribution Maxwellian May be non-Maxwellian
Whereas collisional interactions always lead to a Maxwellian velocity distribution, electric fields influence the particle velocities differently. The velocity dependence of the Coulomb collision cross section can amplify these differences, resulting in phenomena like two-temperature distributions and run-away electrons.
Interactions Binary
Two-particle collisions are the rule, three-body collisions extremely rare.		 Collective
Each particle interacts simultaneously with many others. These collective interactions are about ten times more important than binary collisions.

Complex plasma phenomena

Boltzmann relation. Langmuir coined the name plasma because of its similarity to blood plasma, and Hannes Alfvén noted its cellular nature. Note also the filamentary blue outer shell of X-ray emitting high-speed electrons]] Plasma may exhibit complex behaviour. And just as plasma properties scale over many orders of magnitude (see table above), so do these complex features. Many of these features were first studied in the laboratory, and in more recent years, have been applied to, and recognised throughout the universe. Some of these features include:
- Filamentation, the striations or "stringy things" seen in a "plasma ball", the aurora, lightning, electric arcs, and nebulae. They are caused by larger current densities, and are also called magnetic ropes or plasma cables.
- Double layers, localised charge separation regions that have a large potential difference across the layer, and a vanishing electric field on either side. Double layers are found between adjacent plasmas regions with different physical characteristics, and can accelerate ions and produce synchrotron radiation (such as x-rays and gamma rays).
- Birkeland currents, a magnetic-field-aligned electric current, first observed in the Earth's aurora, and also found in plasma filaments.
- Circuits. Birkeland currents imply electric circuits, that follow Kirchhoff's circuit laws. Circuits have a resistance and inductance, and the behaviour of the plasma depends on the entire circuit. Such circuits also store inductive energy, and should the circuit be disrupted, for example, by a plasma instability, the inductive energy will be released in the plasma.
- Cellular structure. Plasma double layers may separate regions with different properties such as magnetization, density, and temperature, resulting in cell-like regions. Examples include the magnetosphere, heliosphere, and heliospheric current sheet.
- Critical ionization velocity in which the relative velocity between an ionized plasma and a neutral gas, may cause further ionization of the gas, resulting in a greater influence of electomagnetic forces.

Ultracold plasmas

It is also possible to create ultracold plasmas, by using lasers to trap and cool neutral atoms to temperatures of 1 mK or lower. Another laser then ionizes the atoms by giving each of the outermost electrons just enough energy to escape the electrical attraction of its parent ion. The key point about ultracold plasmas is that by manipulating the atoms with lasers, the kinetic energy of the liberated electrons can be controlled. Using standard pulsed lasers, the electron energy can be made to correspond to a temperature of as low as 0.1 K ­ a limit set by the frequency bandwidth of the laser pulse. The ions, however, retain the millikelvin temperatures of the neutral atoms. This type of non-equilibrium ultracold plasma evolves rapidly, and many fundamental questions about its behaviour remain unanswered. Experiments conducted so far have revealed surprising dynamics and recombination behaviour that are pushing the limits of our knowledge of plasma physics.

Mathematical descriptions

Plasmas may be usefully described with various levels of detail. However the plasma itself is described, if electric or magnetic fields are present, then Maxwell's equations will be needed to describe them. The coupling of the description of a conductive fluid to electromagnetic fields is known generally as magnetohydrodynamics, or simply MHD.

Fluid

The simplest possibility is to treat the plasma as a single fluid governed by the Navier Stokes Equations. A more general description is the two-fluid picture, where the ions and electrons are considered to be distinct.

Kinetic

For some cases the fluid description is not sufficient. Kinetic models include information on distortions of the velocity distribution functions with respect to a Maxwell-Boltzmann distribution. This may be important when currents flow, when waves are involved, or when gradients are very steep.

Particle-in-cell

Particle-in-cell (PIC) models include kinetic information by following the trajectories of a large number of individual particles. Charge and current densities are determined by summing the particles in cells which are small compared to the problem at hand but still contain many particles. The electric and magnetic fields are found from the charge and current densities with appropriate boundary conditions. PIC codes for plasma applications were developed at Los Alamos National Laboratory in the 1950's. Although often more calculationally intensive than alternative models, they are relatively easy to understand and program and can be very general.

Fundamental plasma parameters

Los Alamos National Laboratory All quantities are in Gaussian cgs units except temperature expressed in eV and ion mass expressed in units of the proton mass \mu = m_i/m_p; Z is charge state; k is Boltzmann's constant; K is wavelength; γ is the adiabatic index; ln Λ is the Coulomb logarithm.

Frequencies


- electron gyrofrequency, the angular frequency of the circular motion of an electron in the plane perpendicular to the magnetic field: :\omega_ = eB/m_ec = 1.76 \times 10^7 B \mbox
- ion gyrofrequency, the angular frequency of the circular motion of an ion in the plane perpendicular to the magnetic field: :\omega_ = eB/m_ic = 9.58 \times 10^3 Z \mu^ B \mbox
- electron plasma frequency, the frequency with which electrons oscillate when their charge density is not equal to the ion charge density (plasma oscillation): :\omega_ = (4\pi n_ee^2/m_e)^ = 5.64 \times 10^4 n_e^ \mbox
- ion plasma frequency: :\omega_ = (4\pi n_iZ^2e^2/m_i)^ = 1.32 \times 10^3 Z \mu^ n_i^ \mbox
- electron trapping rate :\nu_ = (eKE/m_e)^ = 7.26 \times 10^8 K^ E^ \mbox^
- ion trapping rate :\nu_ = (ZeKE/m_i)^ = 1.69 \times 10^7 Z^ K^ E^ \mu^ \mbox^
- electron collision rate :\nu_e = 2.91 \times 10^ n_e\,\ln\Lambda\,T_e^ \mbox^
- ion collision rate :\nu_i = 4.80 \times 10^ Z^4 \mu^ n_i\,\ln\Lambda\,T_i^ \mbox^

Lengths

plasma oscillation http://history.nasa.gov/SP-345/ch15.htm#250 Ref]]
- Electron thermal de Broglie wavelength, approximate average de Broglie wavelength of electrons in a plasma: :\Lambda_e= \sqrt= 6.919\times 10^\,T_e^\,\mbox
- classical distance of closest approach, the closest that two particles with the elementary charge come to each other if they approach head-on and each have a velocity typical of the temperature, ignoring quantum-mechanical effects: :e^2/kT=1.44\times10^\,T^\,\mbox
- electron gyroradius, the radius of the circular motion of an electron in the plane perpendicular to the magnetic field: :r_e = v_/\omega_ = 2.38\,T_e^B^\,\mbox
- ion gyroradius, the radius of the circular motion of an ion in the plane perpendicular to the magnetic field: :r_i = v_/\omega_ = 1.02\times10^2\,\mu^Z^T_i^B^\,\mbox
- plasma skin depth, the depth in a plasma to which electromagnetic radiation can penetrate: :c/\omega_ = 5.31\times10^5\,n_e^\,\mbox
- Debye length, the scale over which electric fields are screened out by a redistribution of the electrons: :\lambda_D = (kT/4\pi ne^2)^ = 7.43\times10^2\,T^n^\,\mbox

Velocities


- electron thermal velocity, typical velocity of an electron in a Maxwell-Boltzmann distribution: :v_ = (kT_e/m_e)^ = 4.19\times10^7\,T_e^\,\mbox
- ion thermal velocity, typical velocity of an ion in a Maxwell-Boltzmann distribution: :v_ = (kT_i/m_i)^ = 9.79\times10^5\,\mu^T_i^\,\mbox
- ion sound velocity, the speed of the longitudinal waves resulting from the mass of the ions and the pressure of the electrons: :c_s = (\gamma ZkT_e/m_i)^ = 9.79\times10^5\,(\gamma ZT_e/\mu)^\,\mbox
- Alfven velocity, the speed of the waves resulting from the mass of the ions and the restoring force of the magnetic field: :v_A = B/(4\pi n_im_i)^ = 2.18\times10^\,\mu^n_i^B\,\mbox

Dimensionless

waves meeting the heliopause]]
- square root of electron/proton mass ratio :(m_e/m_p)^ = 2.33\times10^ = 1/42.9
- number of particles in a Debye sphere :(4\pi/3)n\lambda_D^3 = 1.72\times10^9\,T^n^
- Alven velocity/speed of light :v_A/c = 7.28\,\mu^n_i^B
- electron plasma/gyrofrequency ratio :\omega_/\omega_ = 3.21\times10^\,n_e^B^
- ion plasma/gyrofrequency ratio :\omega_/\omega_ = 0.137\,\mu^n_i^B^
- thermal/magnetic energy ratio :\beta = 8\pi nkT/B^2 = 4.03\times10^\,nTB^
- magnetic/ion rest energy ratio :B^2/8\pi n_im_ic^2 = 26.5\,\mu^n_i^B^2

Miscellaneous


- Bohm diffusion coefficient :D_B = (ckT/16eB) = 6.25\times10^6\,TB^\,\mbox^2/\mbox
- transverse Spitzer resistivity :\eta_\perp = 1.15\times10^\,Z\,\ln\Lambda\,T^\,\mbox = 1.03\times10^\,Z\,\ln\Lambda\,T^\,\Omega\,\mbox

Fields of active research

Bohm diffusion is so effective at accelerating ions, that electric fields are used in ion drives]] This is just a partial list of topics. A more complete and organised list can be found on the Web site for Plasma science and technology [http://www.plasmas.com/topics.htm].
- Plasma theory
  - Plasma equilibria and stability
  - Plasma interactions with waves and beams
  - Guiding center
  - adiabatic invariant
  - Debye sheath
  - Coulomb collision
- Plasmas in nature
  - The Earth's ionosphere
  - Space plasmas, e.g. Earth's plasmasphere (an inner portion of the magnetosphere dense with plasma)
  - plasma cosmology
- Plasma sources
- Dusty Plasmas
- Plasma diagnostics
  - Thomson scattering
  - Langmuir probe
  - Spectroscopy
  - Interferometry
  - Ionospheric heating
  - Incoherent scatter radar
- Plasma applications
  - Fusion power
    - Magnetic fusion energy (MFE) -- tokamak, stellarator, reversed field pinch, magnetic mirror, dense plasma focus
    - Inertial fusion energy (IFE) (also Inertial confinement fusion — ICF)
    - Plasma-based weaponry
  - Industrial plasmas
    - plasma chemistry
    - plasma processing
    - plasma display

See also

plasma display
- Magnetohydrodynamics
- Electric field screening
- List of plasma physicists
- Large Helical Device
- Important publications in plasma physics

External links


- [http://fusedweb.pppl.gov/CPEP/Chart_Pages/5.Plasma4StateMatter.html Plasmas: the Fourth State of Matter]
- [http://www.plasmas.org/ Plasma Science and Technology]
- [http://plasma-gate.weizmann.ac.il/PlasmaI.html Plasma on the Internet] comprehensive list of plasma related links.
- [http://farside.ph.utexas.edu/teaching/plasma/lectures/lectures.html Introduction to Plasma Physics: a graduate level lecture course given by Richard Fitzpatrick]
- [http://plasmas.org/ An overview of plasma links and applications]
- [http://wwwppd.nrl.navy.mil/nrlformulary/index.html NRL Plasma Formulary online] (or an [http://w3.pppl.gov/~dcoster/nrl/ html version])
- [http://www.plasmacoalition.org/ Plasma Coalition page]
- [http://starfire.ne.uiuc.edu/ Plasma Material Interaction]
- [http://jnaudin.free.fr/html/oa_plasmoid.htm How to build a Stable Plasmoid at One Atmosphere] (requires pre-ignition)
- [http://jnaudin.free.fr/html/oa_plsm4.htm How to build a Stable Plasmoid with this Enhanced Generator] (self-igniting)
- [http://c3po.barnesos.net/homepage/lpl/grapeplasma/ How to make a glowing ball of plasma in your microwave with a grape] Category:Astrophysics ko:플라즈마 ja:プラズマ

Liquid

A liquid (a phase of matter) is a fluid whose volume is fixed under conditions of constant temperature and pressure; and, whose shape is usually determined by the container it fills. Furthermore, liquids exert pressure on the sides of a container as well as on anything within the liquid itself; this pressure is transmitted undiminished in all directions. If a liquid is at rest in a uniform gravitational field, the pressure p at any point is given by :p=\rho gz where \rho is the density of the liquid (assumed constant) and z is the depth of the point below the surface. Note that this formula assumes that the pressure at the free surface is zero, and that surface tension effects may be neglected. Liquids have traits of surface tension and capillarity; they generally expand when heated, and contract when cooled. Objects immersed in liquids are subject to the phenomenon of buoyancy. Liquids at their respective boiling point change to gases, and at their freezing points, change to a solids. Via fractional distillation, liquids can be separated from one another as they vaporise at their own individual boiling points. Cohesion between molecules of liquid is insufficient to prevent those at free surface from evaporating. It should be noted that glass at normal temperatures is not a "supercooled liquid", but a solid. See the article on glass for more details.

See also


- List of phases of matter
- Cooling curve
- Ripple
- Specific gravity
- Liquid dancing Category:Condensed matter physics ko:액체 ms:Cecair ja:液体 simple:Liquid

Category:Electromagnetism

Electromagnetism is the set of phenomena associated with electricity and magnetism.
Electromagnetism
Electricity | Magnetism
Electrostatics Magnetostatics
Electric charge | Coulomb's law | Electric field | Gauss's law | Electric potential Electric current | Ampere's law | Magnetic field | Magnetic moment
Electrodynamics Electrical circuits
Lorentz force law | Electromotive force | Magnetomotive force |Electromagnetic induction | Faraday-Lenz law | Displacement current | Maxwell's equations | Electromagnetic field |Electromagnetic radiation Electrical conduction | Electrical resistance | Capacitance | Inductance | Impedance | Resonant cavities | Waveguides
Category:Physics Category:Special relativity ko:분류:전자기학 ja:Category:電磁気学

Přírodní památka Kladnatá - Grapy

Přírodní památka Kladnatá - Grapy je tvořenaí podmáčenou smrčinou s pestrou mozaikou různých stanovišť - balvanitými svahy se skalními výchozy, rašeliništi a prameništi. Nachází se v nadmořské výšce 765-880 m na jihozápadně exponovaných svazích pod vrcholy Kladnatá (918 m) a Grapy v Radhošťské hornatině v Moravskoslezských Beskydech v CHKO Beskydy.
- Výměra: 62,82 ha
- Katastrální územ:í Horní Bečva, okres Vsetín
- rok vyhlášení: 1999

Důvod ochrany

Posláním přírodní památky je ochrana pestrých přírodních poměrů daných rozmanitostí půdních typů a geomorfologických útvarů (rašeliniště, prameniště, balvanité svahy, skalní výchozy istebňanských vrstev), na které se váže výskyt vzácných a ohrožených druhů rostlin.

Geologie

Geologický podklad tvoří istebňanské vrstvy slezské jednotky. Osu jižní části území tvoří silně rozrušená skalní ostruha. Na jejím úpatí a přilehlých svazích se nachází balvanité sutě a kamenité svahoviny. Severozápadní svah je rozbrázděn stržemi zdrojnic a přítoků potoka Sergač. V členitém reliéfu jsou zastoupeny různorodé půdní typy a geomorfologické útvary.

Flóra

Pestré přírodní podmínky dané rozmanitostí půdních typů a výskytem geomorfologických útvarů podmiňují existenci mnoha druhů a společenstev. Dřevinná skladba je silně pozměněná ve prospěch smrku (Picea abies). Pouze na balvanitých svazích rostou stanovištně vhodné dřeviny - jeřáb ptačí (Sorbus aucuparia) a bříza bělokorá (Betula pendula). Dále se vyskytuje olše lepkavá (Alnus glutinosa), jedle bělokorá (Abies alba) a ojediněle buk lesní (Fagus sylvatica). Na území přírodní památky bylo dosud zaznamenáno 76 druhů cévnatých rostlin a 60 druhů mechorostů. Na zamokřených místech roste např. ostřice ježatá (Carex echinata), prstnatec Fuchsův pravý (Dactylorhiza fuchsii subsp. fuchsii), sítina cibulkatá (Juncus bulbosus), škarda bahenní (Crepis paludosa), violka bahenní (Viola palustris), rašeliníky (Sphagnum sp.), ze vzácnějších druhů mechorostů játrovky ústěnka smutná (Jungermania atrovirens) a stěkovec mnohodílný (Riccardia multifida). Typickými lesními druhy jsou zde kapraďorosty, např. plavuň pučivá (Lycopodium annotinum), plavuň vidlačka (Lycopodium clavatum), vranec jedlový (Huperzia selago), pernatec horský (Lastrea limbosperma), žebrovice různolistá (Blechnum spicant) a přeslička lesní (Equisetum sylvestris). Dále se zde vyskytuje kyčelnice devítilistá (Dentaria enneaphyllos), kýchavice bílá Lobelova (Veratrum album subsp. lobelianum), pstroček dvoulistý (Maianthemum bifolium), na světlinách ve vyšších polohách hořec tolitovitý (Gentiana asclepiadea) aj.

Fauna

Z obojživelníků zde nacházejí vhodné podmínky pro rozmnožování např. ropucha obecná (Bufo bufo), mlok skvrnitý (Salamandra salamandra) a čolek horský (Triturus alpestris), z plazů ještěrka živorodá (Zootoca vivipara), ještěrka obecná (Lacerta agilis) a zmije obecná (Vipera berus). Z ptáků se zde byli pozorováni např. datel černý (Dryocopus martius), kos horský (Turdus torquatus), králíček obecný (Regulus regulus), krkavec velký (Corvus corax), linduška lesní (Anthus trivialis), pěvuška modrá (Prunella modularis) a žluna zelená (Picus viridis). Vyskytuje se zde rys ostrovid (Lynx lynx). kategorie:přírodní památky ČR kategorie:okres Vsetín

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