Gas and Electricity
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Wikipedia-Article "Gas"
- For other uses, see Gas (disambiguation).
A gas is one of the four main phases of matter (after solid and liquid, and followed by plasma), that subsequently appear as a solid material is subjected to increasingly higher temperatures. Thus, as energy in the form of heat is added, a solid (e.g. ice) will first melt to become a liquid (e.g. water), which will then boil or evaporate to become a gas (e.g. water vapor). In some circumstances, a solid (e.g. "dry ice") can directly turn into a gas: this is called sublimation. If the gas is further heated, its atoms or molecules can become (wholly or partially) ionized, turning the gas into a plasma.
In the gas phase, the atoms or molecules constituting the matter basically move independently, with no forces keeping them together or pushing them apart. Their only interactions are rare and random collisions. The particles move in random directions, at high speeds, whose range is dependent on the temperature and defined by the Maxwell-Boltzmann distribution. Therefore, the gas phase is a completely disordered state. Following the second law of thermodynamics, gas particles will immediately diffuse to homogeneously fill any shape or volume of space that is made available to them.
The thermodynamic state of a gas is characterized by its volume, its temperature, which is determined by the average velocity or kinetic energy of the molecules, and its pressure, which is determined by the average velocity and density or number of molecules. These variables are related by the fundamental gas laws, which state that the pressure in an ideal gas is proportional to its temperature and number of molecules, but inversely proportional to its volume.
Like liquids and plasmas, gases are fluids: they have the ability to flow and do not tend to return to their former configuration after deformation, although they do have viscosity. Unlike liquids, however, unconstrained gases do not occupy a fixed volume, but expand to fill whatever space they occupy. The kinetic energy per molecule in a gas is the second greatest of the states of matter (after plasma). Because of this high kinetic energy, gas atoms and molecules tend to bounce off of any containing surface and off one another, the more powerfully as the kinetic energy is increased. A common misconception is that the collisions of the molecules with each other is essential to explain gas pressure, but in fact their random velocities are sufficient to define that quantity. Mutual collisions are important only for establishing the Maxwell-Boltzmann distribution.
Gas particles are normally well separated, as opposed to liquid particles, which are in contact. A material particle (say a dust mote) in a gas moves in Brownian Motion. Since it is at the limit of (or beyond) current technology to observe individual gas particles (atoms or molecules), only theoretical calculations give suggestions as to how they move, but their motion is different from Brownian Motion. The reason is that Brownian Motion involves a smooth drag due to the frictional force of many gas molecules, punctuated by violent collisions of an individual (or several) gas molecule(s) with the particle. The particle (generally consisting of millions or billions of atoms) thus moves in a jagged course, yet not so jagged as we would expect to find if we could examine an individual gas molecule.
Etymology
The word "gas" was apparently coined in the early 17th century by the Belgian chemist Jan Baptist van Helmont, as a re-spelling of his pronunciation of the Greek word chaos.
See also
- Gas laws
- Ideal gas
- Kinetic theory of gases
- Town Gas
- Natural Gas
- List of phases of matter
- Cooling curve
Wikipedia-Article "Electricity"
Electricity is a general term applied to phenomena involving a fundamental property of matter called an electric charge
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Related concepts
In casual usage, the term electricity is applied to several related concepts that are better identified by more precise terms.
- Electric charge: a fundamental conserved property of some subatomic particles, which determines their electromagnetic interactions. Electrically charged matter is influenced by, and produces, electromagnetic fields.
- Electric field is an effect produced by an electric charge that exerts a force on charged objects in its vicinity.
- Electric potential the potential energy per unit charge associated with a static (time-invariant) electric field.
- Electric current: a movement or flow of electrically charged particles.
- Electrical energy: energy made available by the flow of electric charge through a conductor or from the forces between charged particles.
- Electric power: The rate at which electric energy is converted into another form, such as light, heat, or mechanical energy (or converted from another form into electric energy).
History
Ancient
According to Thales of Miletus, writing circa 600 BCE, a form of electricity was known to the Ancient Greeks who found that rubbing fur on various substances, such as amber, would cause a particular attraction between the two. The Greeks noted that the amber buttons could attract light objects such as hair and that if they rubbed the amber for long enough they could even get a spark to jump.
The origin of the word "electricity" is from the Greek word ēlektron, a word the ancient Greeks used for both "amber" and "electrum".
An object found in Iraq in 1938, dated to about 250 BCE and called the Baghdad Battery, resembles a galvanic cell and is believed by some to have been used for electroplating.
Modern
In 1600 the English scientist William Gilbert returned to the subject in De Magnete, and coined the modern Latin word electricus from ηλεκτρον (elektron), the Greek word for "amber", which soon gave rise to the English words electric and electricity. He was followed in 1660 by Otto von Guericke, who is regarded as having invented an early electrostatic generator. Other European pioneers were Robert Boyle, who in 1675 stated that electric attraction and repulsion can act across a vacuum; Stephen Gray, who in 1729 classified materials as conductors and insulators; and C. F. Du Fay, who first identified the two types of electricity that would later be called positive and negative. The Leyden jar, a type of capacitor for electrical energy in large quantities, was invented at Leiden University by Pieter van Musschenbroek in 1745. William Watson, experimenting with the Leyden jar, discovered in 1747 that a discharge of static electricity was equivalent to an electric current.
In June, 1752, Benjamin Franklin promoted his investigations of electricity and theories through the famous, though extremely dangerous, experiment of flying a kite during a thunderstorm. Following these experiments he invented a lightning rod and established the link between lightning and electricity. If Franklin did fly a kite in a storm, he did not do it the way it is often described (as it would have been dramatic but fatal). It was either Franklin (more frequently) or Ebenezer Kinnersley of Philadelphia (less frequently) who created the convention of positive and negative electricity.
Franklin's observations aided later scientists such as Michael Faraday, Luigi Galvani, Alessandro Volta, André-Marie Ampère, and Georg Simon Ohm whose work provided the basis for modern electrical technology. The work of Faraday, Volta, Ampere, and Ohm is honored by society, in that fundamental units of electrical measurement are named after them.
Volta worked with chemicals and discovered that chemical reactions could be used to create positively charged anodes and negatively charged cathodes. When a conductor was attached between these, the difference in the electrical potential (also known as voltage) drives a current between them through the conductor. The potential difference between two points is measured in units of volts in recognition of Volta's work.
The invention of the electric telegraph showed that commercial and practical use could be made of electrical phenomena. By the end of the 19th century electrical engineering became a distinct profession, separate from the physicist or inventor. The late 19th and early 20th century produced such giants of electrical engineering as Nikola Tesla, inventor of the polyphase induction motor; Samuel Morse, inventor of the telegraph; Antonio Meucci, an inventor of the telephone; Thomas Edison inventor of the phonograph and a practical incandescent light bulb; George Westinghouse, inventor of the electric locomotive; Charles Steinmetz, theoretician of alternating current; Alexander Graham Bell, another inventor of the telephone and founder of a successful telephone business.
The rapid advance of electrical technology in the latter 19th and early 20th centuries lead to commercial rivalry such as the so-called War of the Currents), between Edison's direct-current system or Westinghouse's alternating-current method. Often concurrent research in widely scattered locations lead to multiple claims to the invention of a device or system.
Electric charge
- For more details on this topic, see Electric charge.
Electric charge is a property of certain subatomic particles (e.g., electrons and protons) which interacts with electromagnetic fields and causes attractive and repulsive forces between them. Electric charge gives rise to one of the four fundamental forces of nature, and is a conserved property of matter that can be quantified. In this sense, the phrase "quantity of electricity" is used interchangeably with the phrases "charge of electricity" and "quantity of charge." There are two types of charge: we call one kind of charge positive and the other negative. Through experimentation, we find that like-charged objects repel and opposite-charged objects attract one another. The magnitude of the force of attraction or repulsion is given by Coulomb's law.
Electric field
- For more details on this topic, see Electric field.
The concept of electric field was introduced by Michael Faraday. The electrical field force acts between two charges, in the same way that the gravitational field force acts between two masses. However, electric field is a little bit different. Gravitational force depends on the mass of two bodies, whereas electric force depends on the electric charge of two bodies. While gravity can only pull two masses together, the electric force can be an attractive or repulsive force. The criteria for the direction of the forces between two charged bodies is generally proposed as follows:
1) Both charges are of same sign (i.e. both charges are positive) in which case there will be a repulsive force between the two.
2) The charges are opposite in which case there will be an attractive force between the two bodies.
The magnitude of the force is dependent upon the distance between the two bodies, and varies inversely with the square of the distance between them. The magnitude of the force is also directly proportional to the product of the unsigned magnitude of the two charges. The most common experience with electric charge in everyday life is that of static cling - when two particular types of materials are rubbed together, they tend to stick together, at least for a while. This phenomenon occurs because of the exchange of charges between the two materials-- one becomes positively charged while the other becomes negatively charged, and because of their opposite signs there will be a force of attraction between them. Another common experience with electric charge is when one rubs his or her shoes on the carpet while walking and touches a doorknob experiencing a shock. When you rub your feet along the carpet your body acquires a charge, and when you bring your finger close to the doorknob the charges spark off of your finger to discharge.
Electric potential
- For more details on this topic, see Electric potential.
The electric potential difference between two points is defined as the work done per unit charge (against electrical forces) in moving a positive point charge slowly between two points. If one of the points is taken to be a reference point with zero potential, then the electric potential at any point can be defined in terms of the work done per unit charge in moving a positive point charge from that reference point to the point at which the potential is to be determined. For isolated charges, the reference point is usually taken to be infinity. The potential is measured in volts. (1 volt = 1 joule/coulomb) The electric potential is analogous to temperature: there is a different temperature at every point in space, and the temperature gradients indicate the direction of heat flows. Similarly, there is an electric potential at every point in space, and its gradient in the electric field indicates where charges move.
Electric current
- For more details on this topic, see Current (electricity).
The electric charge which occurs naturally within conductors can be forced to flow, while the charges within insulators are locked in place and cannot be moved. Devices that use charge flow principles in materials are called electronic devices. A flow of electric charge is called an electric current. A direct current (DC) is a unidirectional flow; alternating current (AC) is a flow whose time average is zero, but whose energy capability (RMS level) is not zero. With AC the electric current repeatedly changes direction. Electric current is measured in Amperes
Ohm's Law is an important relationship describing the behaviour of electric currents: See also: electrical conduction
For historical reasons, electric current is said to flow from the most positive part of a circuit to the most negative part. The electric current thus defined is called conventional current. It is now known that, depending on the conditions, an electric current can consist of a flow of charged particles in either direction, or even in both directions at once. The positive-to-negative convention is widely used to simplify this situation. If another definition is used - for example, "electron current" - it should be explicitly stated.
Electrical energy
- For more details on this topic, see Electrical energy.
Electrical energy is the flow of electrons or ions. When electrons are flowing through a wire or through hundreds of feet of air in the case of lightning it is because they are being forced to do so by an electrical field. A force is exerted on the electrons and they move. Work is done on the charged particles. A force is pushing them through a distance. More properly, they are moving from outer orbitals of one atom to another, being pushed by the electromotive force. While the electrons are in motion they contain kinetic energy. Consequently, atomic level electricity is a form of kinetic energy.
Electric power
- For more details on this topic, see Electric power.
Electric power is the capacity of the circuit for performing work in a particular amount of time. When a charge moves in a conductor, work is done by that charge. Devices can be made which convert this work into heat (Electric arc furnaces), light (light bulbs and Fluorescent lamps), or motion, i.e. kinetic energy (electric motors).
The unit for all forms of power is the watt (symbol: W). In practice, however, this is generally reserved for the real power component. Apparent power is conventionally expressed in volt-amperes (VA) since it is the simple multiple of rms voltage and current. The unit for reactive power is given the special name "VAR", which stands for volt-amperes-reactive.
SI electricity units
| SI electromagnetic units
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|---|---|---|---|---|
| Symbol | Name of Quantity | Derived Units | Base Units | |
| I | Current | ampere (SI base unit) | A | A |
| q | Electric charge, Quantity of electricity | coulomb | C | A·s |
| V | Potential difference | volt | V | J/C = kg·m2·s−3·A−1 |
| R, Z | Resistance, Impedance, Reactance | ohm | Ω | V/A = kg·m2·s−3·A−2 |
| ρ | Resistivity | ohm metre | Ω·m | kg·m3·s−3·A−2 |
| P | Power, Electrical | watt | W | V·A = kg·m2·s−3 |
| C | Capacitance | farad | F | C/V = kg−1·m−2·A2·s4 |
| Elastance | reciprocal farad | F−1 | V/C = kg·m2·A−2·s−4 | |
| ε | Permittivity | farad per metre | F/m | kg−1·m−3·A2·s4 |
| χe | Electric susceptibility | (dimensionless) | - | - |
| Conductance, Admittance, Susceptance | siemens | S | Ω−1 = kg−1·m−2·s3·A2 | |
| σ | Conductivity | siemens per metre | S/m | kg−1·m−3·s3·A2 |
| H | Magnetic field, magnetic field intensity | ampere per metre | A/m | A·m−1 |
| Φm | Magnetic flux | weber | Wb | V·s = kg·m2·s−2·A−1 |
| B | Magnetic flux density, magnetic induction, magnetic field strength | tesla | T | Wb/m2 = kg·s−2·A−1 |
| Reluctance | ampere-turns per weber | A/Wb | kg−1·m−2·s2·A2 | |
| L | Inductance | henry | H | Wb/A = V·s/A = kg·m2·s−2·A−2 |
| μ | Permeability | henry per metre | H/m | kg·m·s−2·A−2 |
| χm | Magnetic susceptibility | (dimensionless) | - | - |