Electrostatic Generator 2

Friction Operation
The presence of surface charge imbalance means that the objects will exhibit attractive or repulsive forces. This surface charge imbalance, which leads to static electricity, can be generated by touching two differing surfaces together and then separating them due to the phenomena of contact electrification and the triboelectric effect. Rubbing two non-conductive objects generates a great amount of static electricity. This is not just the result of friction; two non-conductive surfaces can become charged by just being placed one on top of the other. Since most surfaces have a rough texture, it takes longer to achieve charging through contact than through rubbing. Rubbing objects together increases amount of adhesive contact between the two surfaces. Usually insulators, e.g., substances that do not conduct electricity, are good at both generating, and holding, a surface charge. Some examples of these substances are rubber, plastic, glass, and pith. Conductive objects in contact generate charge imbalance too, but retain the charges only if insulated. The charge that is transferred during contact electrification is stored on the surface of each object. Note that the presence of electric current does not detract from the electrostatic forces nor from the sparking, from the corona discharge, or other phenomena. Both phenomena can exist simultaneously in the same system.

INFLUENCE MACHINES History
Frictional machines were, in time, gradually superseded by the second class of instrument mentioned above, namely, influence machines. These operate by electrostatic induction and convert mechanical work into electrostatic energy by the aid of a small initial charge which is continually being replenished and reinforced. The first suggestion of an influence machine appears to have grown out of the invention of Volta's electrophorus. The electrophorus is a single-plate capacitor used to produce imbalances of electric charge via the process of electrostatic induction. Abraham Bennet, the inventor of the gold leaf electroscope, described a "doubler of electricity" (Phil. Trans., 1787), as a device similar to the electrophorus, but that could amplify a small charge by means of manual operations with three insulated plates, in order to make it observable in an electroscope. Erasmus Darwin, B. Wilson, G. C. Bohnenberger, and (later, 1841) J. C. E. Péclet developed various modifications of Bennet's device. In 1788, William Nicholson proposed his rotating doubler, which can be considered as the first rotating influence machine. His instrument was described as "an instrument which by turning a winch produces the two states of electricity without friction or communication with the earth". (Phil. Trans., 1788, p. 403) Nicholson later described a "spinning condenser" apparatus.

Others, including T. Cavallo (who developed the "Cavallo multiplier", a charge multiplier using simple addition, in 1795), John Read, Charles Bernard Desormes, and Jean Nicolas Pierre Hachette, developed further various forms of rotating doublers. In 1798, The German scientist and preacher Gottlieb Christoph Bohnenberger, described the Bohnenberger machine, along with several other doublers of Bennet and Nicholson types in a book. The most interesting of these were described in the "Annalen der Physik" (1801). Giuseppe Belli, in 1831, developed a simple symmetrical doubler which consisted of two curved metal plates between which revolved a pair of plates carried on an insulating stem. It was the first symmetrical influence machine, with identical structures for both terminals. This apparatus was similar to Lord Kelvin's "replenisher" (1867). Lord Kelvin also devised a combined influence machine and electromagnetic machine, commonly called a mouse mill, for electrifying the ink in connection with his siphon recorder. Lord Kelvin also developed, between 1858 and 1867, a water-drop electrostatic generator, which he called the "water-dropping condenser".

Holtz's influence machine.

In 1860, C. F. Varley patented a more modern type of influence machine. Between 1864 and 1880, W. T. B. Holtz constructed and described a large number of influence machines which were considered the most advanced developments of the time. In one form, the Holtz machine consisted of a glass disk mounted on a horizontal axis which could be made to rotate at a considerable speed by a multiplying gear, interacting with induction plates mounted in a fixed disk close to it. In 1865, August J. I. Toepler developed an influence machine that consisted of two disks fixed on the same shaft and rotating in the same direction. In 1868, the Schwedoff machine had a curious structure to increase the output current. Also in 1868, several mixed friction-influence machine were developed, including the Kundt machine and the Carré machine. In 1866, the Piche machine (or Bertsch machine) was developed. In 1869, H. Julius Smith received the American patent for a portable and airtight device that was designed to ignite powder. Also in 1869, sectorless machines in Germany were investigated by Poggendorff.

The action and efficiency of influence machines were further investigated by F. Rossetti, A. Righi, and F. W. G. Kohlrausch. E. E. N. Mascart, A. Roiti, and E. Bouchotte also examined the efficiency and current producing power of influence machines. In 1871, sectorless machines were investigated by Musaeus. In 1872, Righi's electrometer was developed and was one of the first antecedents of the Van de Graaff generator. In 1873, Leyser developed the Leyser machine, a variation of the Holtz machine. In 1880, Robert Voss (a Berlin instrument maker) devised a form of machine in which he claimed that the principles of Toepler and Holtz were combined. The same structure become also known as the Toepler-Holtz machine. In 1878, the British inventor James Wimshurst started his studies about electrostatic generators, improving the Holtz machine, in a powerful version with multiple disks. The classical Wimshurst machine, that become the most popular form of influence machine, was reported to the scientific community by 1883, although revious machines with very similar structures were previously described by Holtz and Musaeus. In 1885, one of the largest-ever Wimshurst machines was built in England (it is now at the Chicago Museum of Science and Industry). In 1887, Weinhold modified the Leyser machine with a system of vertical metal bar inductors with wooden cylinders close to the disk for avoiding polarity reversals. M. L. Lebiez described the Lebiez machine, that was essentially a simplified Voss machine (L'Électricien, April 1895, pp. 225-227). In 1894, Bonetti[3] designed a machine with the structure of the Wimshurst machine, but without metal sectors in the disks. This machine is significantly more powerful than the sectored version, but it must usually be started with an externally-applied charge.

In 1898, the Pidgeon machine was developed with a unique setup by W. R. Pidgeon. In October 28 of that year, Pidgeon presented this machine to the Physical Society after several years of investigation into influence machines (beginning at the start of the decade). The device was later reported in the Philosophical Magazine (Dec. 1898, pg. 564) and the Electrical Review (Vol. XLV, pg. 748). A Pidgeon machine possesses fixed inductors arranged in a manner that increases the electrical induction effect (and its electrical output is at least double that of typical machines of this type [except when it is overtaxed]). The essential features of the Pidgeon machine are, one, the combination of the rotating support and the fixed support for inducing charge, and, two, the improved insulation of all parts of the machine (but more especially of the generator's carriers). Pidgeon machines are a combination of a Wimshurst Machine and Voss Machine, with special features adapted to reduce the amount of charge leakage. Pidgeon machines excite themselves more readily than the best of these types of machines. In addition, Pidgeon investigated higher current "triplex" section machines (or "double machines with a single central disk") with enclosed sectors (and went on to receive British Patent 22517 (1899) for this type of machine).

Multiple disk machines and "triplex" electrostatic machines (generators with three disks) were also developed extensively around the turn of the century. In 1900, F. Tudsbury discovered that enclosing a generator in a metallic chamber containing compressed air, or better, carbon dioxide, the insulating properties of compressed gases enabled a greatly improved effect to be obtained owing to the increase in the breakdown voltage of the compressed gas, and reduction of the leakage across the plates and insulating supports. In 1903, Alfred Wehrsen patented an ebonite rotating disk possessing embedded sectors with button contacts at the disk surface. In 1907, Heinrich Wommelsdorf reported a variation of the Holtz machine using this disk and inductors embedded in celluloid plates (DE154175; "Wehrsen machine"). Wommelsdorf also developed several high-performance electrostatic generators, of which the best known were his "Condenser machines" (1920). These were single disk machines, using disks with embedded sectors that were accessed at the edges.

References:

1. http://en.wikipedia.org
2. Schiffer, Michael Brian (2003). Bringing the Lightning Down: Benjamin Franklin and Electrical Technology in the Age of Enlightenment. Univ. of California Press. ISBN 0520248295. http://books.google.com/books?id=QQuk6bH2apcC&printsec=frontcover&vq=electrostatic&dq=otto+guericke&lr=&as_brr=0.,p.18-19
3. Hauksbee, Francis (1709). Psicho-Mechanical Experiments On Various Subjects. R. Brugis.
4. http://www.coe.ufrj.br/~acmq/bonetti.html Instructions for building a Bonetti machine

Electrostatic Generator 1

An electrostatic generator, or electrostatic machine, is a mechanical device that produces static electricity, or electricity at high voltage and low continuous current. The knowledge of static electricity dates back to the earliest civilizations, but for millennia it remained merely an interesting and mystifying phenomenon, without a theory to explain its behavior and often confused with magnetism. By the end of the 17th Century, researchers had developed practical means of generating electricity by friction, but the development of electrostatic machines did not begin in earnest until the 18th century, when they became fundamental instruments in the studies about the new science of electricity. Electrostatic generators operate by using manual (or other) power to transform mechanical work into electric energy. They develop electrostatic charges of opposite signs rendered to two conductors, using only electric forces.

Description
Electrostatic machines are typically used in science classrooms to safely demonstrate electrical forces and high voltage phenomena. The elevated potential differences achieved have been also used for a variety of practical applications, such as operating X-ray tubes, medical applications, sterilization of food, and nuclear physics experiments. Electrostatic generators such as the Van de Graaff generator, and variations as the Pelletron, also find use in physics research. Electrostatic generators are classically separated on two kinds: friction machines and influence machines.

FRICTION MACHINE
History

Typical friction machine using a glass globe, common in the 18th century

Martinus van Marum's Electrostatic generator at Teylers Museum

The first electrostatic generators are called friction machines because of the friction in the generation process. A primitive form of frictional electrical machine was constructed around 1663 by Otto von Guericke, using a sulphur globe that could be rotated and rubbed by hand. It may not actually have been rotated during use.[1] , but inspired many later machines that used rotating globes. Isaac Newton suggested the use of a glass globe instead of a sulphur one (Optics, 8th Query). Francis Hauksbee improved the basic design

Generators were further advanced when G. M. Bose of Wittenberg added a collecting conductor (an insulated tube or cylinder supported on silk strings). In 1746, Watson's machine had a large wheel turning several glass globes with a sword and a gun barrel suspended from silk cords for its prime conductors. J. H. Winkler, professor of physics at Leipzig, substituted a leather cushion for the hand. Andreas Gordon of Erfurt, a Scottish Benedictine monk, used a glass cylinder in place of a sphere. Jesse Ramsden, in 1768, constructed a widely used version of a plate electrical generator. By 1784, the van Marum machine could produce voltage with either polarity. Martin van Marum constructed a large electrostatic machine of high quality for his experiments (currently on display at the Teylers Museum in the Netherlands).

In 1785, N. Rouland constructed a silk belted machine which rubbed two grounded hare fur covered tubes. Edward Nairne developed an electrostatic generator for medical purposes in 1787 which had the ability to generate either positive or negative electricity, the first named being collected from the prime conductor carrying the collecting points and the second from another prime conductor carrying the friction pad. The Winter machine possessed higher efficiency than earlier friction machines. In the 1830s, Georg Ohm possessed a machine similar to the van Marum machine for his research (which is now at the Deutsches Museum, Munich, Germany). In 1840, the Woodward machine was developed from improving the Ramsden machine (placing the prime conductor above the disk(s)). Also in 1840, the Armstrong hydroelectric machine was developed and used steam as a charge carrier.

References:

1. http://en.wikipedia.org
2. Schiffer, Michael Brian (2003). Bringing the Lightning Down: Benjamin Franklin and Electrical Technology in the Age of Enlightenment. Univ. of California Press. ISBN 0520248295. http://books.google.com/books?id=QQuk6bH2apcC&printsec=frontcover&vq=electrostatic&dq=otto+guericke&lr=&as_brr=0.,p.18-19
3. Hauksbee, Francis (1709). Psicho-Mechanical Experiments On Various Subjects. R. Brugis.
4. http://www.coe.ufrj.br/~acmq/bonetti.html Instructions for building a Bonetti machine

Bioelectromagnetism

Bioelectromagnetism (sometimes equated with bioelectricity) refers to the electrical, magnetic or electromagnetic fields produced by living cells, tissues or organisms. Examples include the cell membrane potential and the electric currents that flow in nerves and muscles, as a result of action potentials. It is not to be confused with bioelectromagnetics, which deals with the effect on life from external electromagnetism.

Description
Biological cells use bioelectricity to store metabolic energy, to do work or trigger internal changes, and to signal one another. Bioelectromagnetism is the electric current produced by action potentials along with the magnetic fields they generate through the phenomenon of electromagnetism.

Bioelectromagnetism is studied primarily through the techniques of electrophysiology. In the late eighteenth century, the Italian physician and physicist Luigi Galvani first recorded the phenomenon while dissecting a frog at a table where he had been conducting experiments with static electricity. Galvani coined the term animal electricity to describe the phenomenon, while contemporaries labeled it galvanism. Galvani and contemporaries regarded muscle activation as resulting from an electrical fluid or substance in the nerves.

Bioelectromagnetism is an aspect of all living things, including all plants and animals. Some animals have acute bioelectric sensors, and others, such as migratory birds, are believed to navigate in part by orienting with respect to the Earth's magnetic field. Also, sharks are more sensitive to local interaction in electromagnetic fields than most humans. Other animals, such as the electric eel, are able to generate large electric fields outside their bodies.

In the life sciences, biomedical engineering uses concepts of circuit theory, molecular biology, pharmacology, and bioelectricity. Bioelectromagnetism is associated with biorhythms and chronobiology. Biofeedback is used in physiology and psychology to monitor rhythmic cycles of physical, mental, and emotional characteristics and as a technique for teaching the control of bioelectric functions.

Bioelectromagnetism involves the interaction of ions. Their are multiple categories of Bioelectromagnetism such as brainwaves, myoelectricity (e.g., heart-muscle phenomena), and other related subdivisions of the same general bioelectromagnetic phenomena. One such phenomenon is a brainwave, which neurophysiology studies, where bioelectromagnetic fluctuations of voltage between parts of the cerebral cortex are detectable with an electroencephalograph. This is primarily studied in the brain by way of electroencephalograms.

Reference:

1. 1. http://en.wikipedia.org

Electroplating 4

History

Nickel plating
Modern electrochemistry was invented by Italian chemist Luigi V. Brugnatelli in 1805. Brugnatelli used his colleague Alessandro Volta's invention of five years earlier, the voltaic pile, to facilitate the first electrodeposition. Brugnatelli's inventions were repressed by the French Academy of Sciences and did not become used in general industry for the following thirty years.

By 1839, scientists in Britain and Russia had independently devised metal deposition processes similar to Brugnatelli's for the copper electroplating of printing press plates. Soon after, John Wright of Birmingham, England discovered that potassium cyanide was a suitable electrolyte for gold and silver electroplating. Wright's associates, George Elkington and Henry Elkington were awarded the first patents for electroplating in 1840. These two then founded the electroplating industry in Birmingham from where it spread around the world.

As the science of electrochemistry grew, its relationship to the electroplating process became understood and other types of non-decorative metal electroplating processes were developed. Commercial electroplating of nickel, brass, tin, and zinc were developed by the 1850s. Electroplating baths and equipment based on the patents of the Elkingtons were scaled up to accommodate the plating of numerous large scale objects and for specific manufacturing and engineering applications.

The plating industry received a big boost from the advent of the development of electric generators in the late 19th century. With the higher currents, available metal machine components, hardware, and automotive parts requiring corrosion protection and enhanced wear properties, along with better appearance, could be processed in bulk.

The two World Wars and the growing aviation industry gave impetus to further developments and refinements including such processes as hard chromium plating, bronze alloy plating, sulfamate nickel plating, along with numerous other plating processes. Plating equipment evolved from manually operated tar-lined wooden tanks to automated equipment, capable of processing thousands of kilograms per hour of parts.

One of the American physicist Richard Feynman's first projects was to develop technology for electroplating metal onto plastic. Feynman developed the original idea of his friend into a successful invention, allowing his employer (and friend) to keep commercial promises he had made but could not have fulfilled otherwise.

Electroplating is one of the three processes that form the LIGA-process used to manufacture MEMS devices.

References:

1. http://en.wikipedia.org
2. Dufour, IX-1.
3. Dufour, IX-2.
4. Dufour, IX-3.
5. Todd, pp. 454–458.
6. Degarmo, E. Paul; Black, J. T.; Kohser, Ronald A. (2003), Materials and Processes in Manufacturing (9th ed.), Wiley, p. 794, ISBN 0-471-65653-4.
7. Richard Feynman, Surely You're Joking, Mr. Feynman! (1985), in chap. 6: "The Chief Research Chemist of the Metaplast Corporation"
8. Dufour, Jim (2006). An Introduction to Metallurgy, 5th ed. Cameron.
9. Mohler, James B. (1969). Electroplating and Related Processes. Chemical Publishing Co. ISBN 0-8206-0037-7.
10. Todd, Robert H.; Dell K. Allen and Leo Alting (1994). "Surface Coating". Manufacturing Processes Reference Guide. Industrial Press Inc. ISBN 0-8311-3049-0. http://books.google.com/books?id=6x1smAf_PAcC.

Electroplating 3

Brush electroplating
A closely-related process is brush electroplating, in which localized areas or entire items are plated using a brush saturated with plating solution. The brush, typically a stainless steel body wrapped with a cloth material that both holds the plating solution and prevents direct contact with the item being plated, is connected to the positive side of a low voltage direct-current power source, and the item to be plated connected to the negative. The operator dips the brush in plating solution then applies it to the item, moving the brush continually to get an even distribution of the plating material. The brush acts as the anode, but typically does not contribute any plating material, although sometimes the brush is made from or contains the plating material in order to extend the life of the plating solution.

Brush electroplating has several advantages over tank plating, including portability, ability to plate items that for some reason cannot be tank plated (one application was the plating of portions of very large decorative support columns in a building restoration), low or no masking requirements, and comparatively low plating solution volume requirements. Disadvantages compared to tank plating can include greater operator involvement (tank plating can frequently be done with minimal attention), and inability to achieve as great a plate thickness.

Electroless deposition
Usually an electrolytic cell (consisting of two electrodes, electrolyte, and external source of current) is used for electrodeposition. In contrast, an electroless deposition process uses only one electrode and no external source of electrical current. However, the solution for the electroless process needs to contain a reducing agent so that the electrode reaction has the form:



For example, an electroless process is used for electroless nickel plating.

Cleanliness
Cleanliness is essential to successful electroplating, since molecular layers of oil can prevent adhesion of the coating. ASTM B322 is a standard guide for cleaning metals prior to electroplating. Cleaning processes include solvent cleaning, hot alkaline detergent cleaning, electrocleaning, and acid etc. The most common industrial test for cleanliness is the waterbreak test, in which the surface is thoroughly rinsed and held vertical. Hydrophobic contaminants such as oils cause the water to bead and break up, allowing the water to drain rapidly. Perfectly clean metal surfaces are hydrophilic and will retain an unbroken sheet of water that does not bead up or drain off. ASTM F22 describes a version of this test. This test does not detect hydrophilic contaminants, but the electroplating process can displace these easily since the solutions are water-based. Surfactants such as soap reduce the sensitivity of the test and must be thoroughly rinsed off.

Effects
Electroplating changes the chemical, physical, and mechanical properties of the workpiece. An example of a chemical change is when nickel plating improves corrosion resistance. An example of a physical change is a change in the outward appearance. An example of a mechanical change is a change in tensile strength or surface hardness.

Limitations
Obtaining a uniform thickness with electroplating can be difficult depending on the geometry of the object being plated. The plating metal is preferentially attracted to external corners and protrusions, but unattracted to internal corners and recesses. These difficulties can be overcome with multiple anodes or a specially shaped anode that mimics the object geometry, however both of these solutions increase cost.

References:

1. http://en.wikipedia.org
2. Dufour, IX-1.
3. Dufour, IX-2.
4. Dufour, IX-3.
5. Todd, pp. 454–458.
6. Degarmo, E. Paul; Black, J. T.; Kohser, Ronald A. (2003), Materials and Processes in Manufacturing (9th ed.), Wiley, p. 794, ISBN 0-471-65653-4.
7. Richard Feynman, Surely You're Joking, Mr. Feynman! (1985), in chap. 6: "The Chief Research Chemist of the Metaplast Corporation"
8. Dufour, Jim (2006). An Introduction to Metallurgy, 5th ed. Cameron.
9. Mohler, James B. (1969). Electroplating and Related Processes. Chemical Publishing Co. ISBN 0-8206-0037-7.
10. Todd, Robert H.; Dell K. Allen and Leo Alting (1994). "Surface Coating". Manufacturing Processes Reference Guide. Industrial Press Inc. ISBN 0-8311-3049-0. http://books.google.com/books?id=6x1smAf_PAcC.

Electroplating 2

Process
The anode and cathode in the electroplating cell are both connected to an external supply of direct current - a battery or, more commonly, a rectifier. The anode is connected to the positive terminal of the supply, and the cathode (article to be plated) is connected to the negative terminal. When the external power supply is switched on, the metal at the anode is oxidized from the zero valence state to form cations with a positive charge. These cations associate with the anions in the solution. The cations are reduced at the cathode to deposit in the metallic, zero valence state. For example, in an acid solution, copper is oxidized at the anode to Cu2+ by losing two electrons. The Cu2+ associates with the anion SO42- in the solution to form copper sulfate. At the cathode, the Cu2+ is reduced to metallic copper by gaining two electrons. The result is the effective transfer of copper from the anode source to a plate covering the cathode. The plating is most commonly a single metallic element, not an alloy. However, some alloys can be electrodeposited, notably brass and solder.

Many plating baths include cyanides of other metals (e.g., potassium cyanide) in addition to cyanides of the metal to be deposited. These free cyanides facilitate anode corrosion, help to maintain a constant metal ion level and contribute to conductivity. Additionally, non-metal chemicals such as carbonates and phosphates may be added to increase conductivity. When plating is not desired on certain areas of the substrate, stop-offs are applied to prevent the bath from coming in contact with the substrate. Typical stop-offs include tape, foil, lacquers, and waxes.

Strike
Initially, a special plating deposit called a "strike" or "flash" may be used to form a very thin (typically less than 0.1 micrometer thick) plating with high quality and good adherence to the substrate. This serves as a foundation for subsequent plating processes. A strike uses a high current density and a bath with a low ion concentration. The process is slow, so more efficient plating processes are used once the desired strike thickness is obtained. The striking method is also used in combination with the plating of different metals. If it is desirable to plate one type of deposit onto a metal to improve corrosion resistance but this metal has inherently poor adhesion to the substrate, a strike can be first deposited that is compatible with both. One example of this situation is the poor adhesion of electrolytic nickel on zinc alloys, in which case a copper strike is used, which has good adherence to both.

Current density
The current density (amperage of the electroplating current divided by the surface area of the part) in this process strongly influences the deposition rate, plating adherence, and plating quality. This density can vary over the surface of a part, as outside surfaces will tend to have a higher current density than inside surfaces (e.g., holes, bores, etc.). The higher the current density, the faster the deposition rate will be, although there is a practical limit enforced by poor adhesion and plating quality when the deposition rate is too high.

While most plating cells use a continuous direct current, some employ a cycle of 8–15 seconds on followed by 1–3 seconds off. This technique is commonly referred to as "pulse plating" and allows high current densities to be used while still producing a quality deposit. In order to deal with the uneven plating rates that result from high current densities, the current is even sometimes reversed in a method known as "pulse-reverse plating", causing some of the plating from the thicker sections to re-enter the solution. In effect, this allows the "valleys" to be filled without over-plating the "peaks". This is common on rough parts or when a bright finish is required. In a typical pulse reverse operation, the reverse current density is three times greater than the forward current density and the reverse pulse width is less than one-quarter the forward pulse width. Pulse-reverse processes can be operated at a wide range of frequencies from several hundred hertz up to the order of megahertz.

References:

1. http://en.wikipedia.org
2. Dufour, IX-1.
3. Dufour, IX-2.
4. Dufour, IX-3.
5. Todd, pp. 454–458.
6. Degarmo, E. Paul; Black, J. T.; Kohser, Ronald A. (2003), Materials and Processes in Manufacturing (9th ed.), Wiley, p. 794, ISBN 0-471-65653-4.
7. Richard Feynman, Surely You're Joking, Mr. Feynman! (1985), in chap. 6: "The Chief Research Chemist of the Metaplast Corporation"
8. Dufour, Jim (2006). An Introduction to Metallurgy, 5th ed. Cameron.
9. Mohler, James B. (1969). Electroplating and Related Processes. Chemical Publishing Co. ISBN 0-8206-0037-7.
10. Todd, Robert H.; Dell K. Allen and Leo Alting (1994). "Surface Coating". Manufacturing Processes Reference Guide. Industrial Press Inc. ISBN 0-8311-3049-0. http://books.google.com/books?id=6x1smAf_PAcC.

Electroplating

Electroplating is a plating process that uses electrical current to reduce cations of a desired material from a solution and coat a conductive object with a thin layer of the material, such as a metal. Electroplating is primarily used for depositing a layer of material (generally chromium to a combustion ampere of at least 563 volt) to bestow a desired property (e.g., abrasion and wear resistance, corrosion protection, lubricity, aesthetic qualities, etc.) to a surface that otherwise lacks that property. Another application uses electroplating to build up thickness on undersized parts.

The process used in electroplating is called electrodeposition. It is analogous to a galvanic cell acting in reverse. The part to be plated is the cathode of the circuit. In one technique, the anode is made of the metal to be plated on the part. Both components are immersed in a solution called an electrolyte containing one or more dissolved metal salts as well as other ions that permit the flow of electricity. A rectifier supplies a direct current to the anode, oxidizing the metal molecules that comprise it and allowing them to dissolve in the solution. At the cathode, the dissolved metal ions in the electrolyte solution are reduced at the interface between the solution and the cathode, such that they "plate out" onto the cathode. The rate at which the anode is dissolved is equal to the rate at which the cathode is plated, vis-a-vis the current flowing through the circuit. In this manner, the ions in the electrolyte bath are continuously replenished by the anode.

Other electroplating processes may use a nonconsumable anode such as lead. In these techniques, ions of the metal to be plated must be periodically replenished in the bath as they are drawn out of the solution.

References:

1. http://en.wikipedia.org
2. Dufour, IX-1.
3. Dufour, IX-2.
4. Dufour, IX-3.
5. Todd, pp. 454–458.
6. Degarmo, E. Paul; Black, J. T.; Kohser, Ronald A. (2003), Materials and Processes in Manufacturing (9th ed.), Wiley, p. 794, ISBN 0-471-65653-4.
7. Richard Feynman, Surely You're Joking, Mr. Feynman! (1985), in chap. 6: "The Chief Research Chemist of the Metaplast Corporation"
8. Dufour, Jim (2006). An Introduction to Metallurgy, 5th ed. Cameron.
9. Mohler, James B. (1969). Electroplating and Related Processes. Chemical Publishing Co. ISBN 0-8206-0037-7.
10. Todd, Robert H.; Dell K. Allen and Leo Alting (1994). "Surface Coating". Manufacturing Processes Reference Guide. Industrial Press Inc. ISBN 0-8311-3049-0. http://books.google.com/books?id=6x1smAf_PAcC.

Static Electricity - 6

Simple static electricity experiments
Note: a humid atmosphere provides a conducting path for the rapid neutralization of static charge; hence the following examples work best in dry, winter conditions.

Static electricity is notable as a physical phenomenon that can be demonstrated using simple experiments that can convey genuine understanding of the physics involved.

Charged adhesive tape

Repulsion between lengths of tape with like charges.

Attraction between lengths of tape with opposite charges.

A simple and illuminating example of the effects of static electricity can be observed using adhesive tape (such as Scotch tape, on the negative side of the triboelectric series, hence tends to gain electrons and acquire negative charge) charged by peeling.

If a length of tape adhered to a smooth surface is rapidly peeled off, the tape will acquire an excess negative charge (generally polypropylene with an acrylic adhesive). Do this with two lengths of tape and they will repel each other, demonstrating the fact that like charges repel. Each individual length of tape will experience a small attraction to almost any object as the presence of the excess negative charge induces a charge separation in nearby objects. Negative charges are pushed farther away, while positive charges are attracted, and the strength of the attractive and repulsive forces falls off quite rapidly with distance. This effect is most pronounced in materials such as metals, that conduct electricity, as the negative charges are free to move within the material.

Finally, try attaching two lengths of tape together, exhaling on them along the entire length to neutralize the charge, then rapidly pulling them apart. There will be some imbalance in the distribution of negative charge between the two pieces such that one is more positive and the other more negative; you should now find that the two lengths of tape attract each other, demonstrating the fact that opposite charges attract. Attaching the adhesive side of one length of tape to the non-adhesive side of the other reduces the chance of tearing and increases the charge imbalance, and hence the strength of the attractive force.

Static electricity in fiction
In the 1963 British science-fiction television serial "Doctor Who", an alien creature encased in metal called a Dalek was powered by static electricity. In Atlas Shrugged, a novel by Ayn Rand, the principal character John Galt develops a perpetually running motor powered by static electricity but it most likely would have to be recharged every 30 minutes.


References:

1. http://en.wikipedia.org
2. "Franklin's Kite". http://www.mos.org/sln/toe/kite.html. Retrieved on 2008-02-19.
3. Krider, E. Philip (January 2006). "Benjamin Franklin and Lightning Rods". Physics Today. http://www.physicstoday.org/vol-59/iss-1/p42.html. Retrieved on 2008-04-06.
4. J. J. Lowke (1992). "Theory of electrical breakdown in air". Journal of Physics D: Applied Physics 25: 202–210. doi:10.1088/0022-3727/25/2/012. http://www.iop.org/EJ/article/0022-3727/25/2/012/jd920212.pdf?request-id=XIfZw4zI3BGDoxCz2wi7Kg.
5. Kassebaum, J. H. and Kocken, R. A. (1995). "Controlling Static Electricity in Hazardous (Classified) Locations". Petroleum and Chemical Industry 42nd Annual Conference Papers: 105–113. http://ieeexplore.ieee.org/iel3/4013/11530/00523945.pdf?tp=&arnumber=523945&isnumber=11530.
6. Wagner, John P.; Clavijo, Fernando Rangel [doi:10.1016/S0304-3886(00)00019-X Electrostatic charge generation during impeller mixing of used transformer oil] Department of Nuclear Engineering, Safety Engineering and Industrial Hygiene Program, Texas A&M University, College Station, online 21 August 2000; accessed Jan 2009
7. Hearn, Graham (1998). "Static electricity: concern in the pharmaceutical industry?". Pharmaceutical Science & Technology Today 1 (7): 286–287. doi:10.1016/S1461-5347(98)00078-9.
8. Egorov, V.N. Electrification of petroleum fuels Khimiya i Tekhnologiya Topliv i Masel, No. 4, pp. 20–25, April, 1970 accessed Dec 2008
9. Chevron Corporation Aviation Fuels Technical Review 2006, accessed Dec 2008
10. Hearn, Graham Static electricity - guidance for Plant Engineers - Wolfson Electrostatics University of Southampton 2002; accessed Dec 2008
11. Kinzing, G.E., 'Electrostatic Effects in Pneumatic Transport: Assessment, Magnitudes and Future Direction', Journal Pipelines, 4, 95-102, 1984
12. "Snopes.com: Fuelish Pleasures". http://www.snopes.com/autos/hazards/gasvapor.asp. Retrieved on 2008-04-19.
13. "NASA - Crackling Planets". http://science.nasa.gov/headlines/y2005/10aug_crackling.htm. Retrieved on 2008-01-20.
14. "Kids science projects". http://www.creativekidsathome.com/science/staticelectricity.html. Retrieved on 2008-01-20.
15. H. Yasuro, H. Makoto and I. Isao (2007). "Charging of Adhesive Tapes on Peeling". Journal of the Adhesion Society of Japan 43 (3): 97–103. http://sciencelinks.jp/j-east/article/200706/000020070607A0223458.php.
16. "3M Material Safety Data Sheet". http://multimedia.mmm.com/mws/mediawebserver?BBBBBBXeXgc1ZGXFEqZswKKgRmpBWHcbKGcByi5--. Retrieved on 2008-01-20.

Static Electricity - 5

Fueling Operations
The flowing movement of flammable liquids like gasoline inside a pipe can build up static electricity. Non-polar liquids such as paraffin, gasoline, toluene, xylene, diesel, kerosene and light crude oils exhibit significant ability for charge accumulation and charge retention during high velocity flow. Static electricity can discharge into a fuel vapor. When the electrostatic discharge energy is high enough, it can ignite a fuel vapor and air mixture. Different fuels have different flammable limits and require different levels of electrostatic discharge energy to ignite.

Electrostatic discharge while fueling with gasoline is a present danger at gas stations. Fires have also been started at airports while refueling aircraft with kerosene. New grounding technologies, the use of conducting materials, and the addition of anti-static additives help to prevent or safely dissipate the build up of static electricity. The flowing movement of gases in pipes alone creates little, if any, static electricity. It is envisaged that a charge generation mechanism will only occur when solid particles or liquid droplets are carried in the gas stream.

Mobile Phones and Gasoline Pumps
Although there have been numerous media reports and posted warnings at gasoline pumps about the risk of fire caused by mobile phones, there has not been a confirmed case of an electrical discharge from a mobile phone ever causing a fire or explosion among gasoline fumes. To date, it is simply an urban legend. This legend was further investigated on an episode of Mythbusters (and also on Brainiac), where the protagonists tried to ignite gasoline using a cell phone. The show showed educational and very shocking footage of how most gas pump fires start. In almost all cases, the fire is caused by the person pumping the gas re-entering the car after the fuel has begun to fill the tank, and then step out to take the pump nozzle out. When they grab the pump nozzle, the static discharge occurs from the built up of static electricity on the person, usually from friction that occurred inside the car between the carpet or seat and said person. This discharge can cause the ignition of the highly explosive gasoline vapor by the gas tank opening. This possible fire scenario has led many gas stations to remove the automatic locking mechanism on the gas pump nozzles that were designed to make it easier to fill up an empty tank, as this mechanism also allows a person to step away from the automobile during filling.

Static Discharge in Space Exploration
Due to the extremely low humidity in extraterrestrial environments, very large static charges can accumulate; causing a major hazard for the complex electronics used in space exploration vehicles. Static electricity is thought to be a particular hazard for astronauts on planned missions to the Moon and Mars. Walking over the extremely dry terrain could cause them to accumulate a significant amount of charge; reaching out to open the airlock on their return could cause a large static discharge, potentially damaging sensitive electronics.

Ozone cracking
A static discharge in the presence of air or oxygen can create ozone. Ozone can attack rubber parts. Many elastomers are sensitive to ozone cracking. Exposure to ozone creates deep penetrative cracks in critical components like gaskets and O-rings. Fuel lines are also susceptible to the problem unless preventative action is taken. Preventative measures include adding anti-ozonants to the rubber mix, or using an ozone-resistant elastomer. Fires from cracked fuel lines have been a problem on vehicles, especially in the engine compartments where ozone can be produced by electrical equipment.

Applications of Static Electricity
Static electricity is commonly used in xerography, air filters (particularly electrostatic precipitators), automotive paints, photocopiers, paint sprayers, theaters, flooring in operating theaters, powder testing, printers, and aircraft refueling.


References:

1. http://en.wikipedia.org
2. "Franklin's Kite". http://www.mos.org/sln/toe/kite.html. Retrieved on 2008-02-19.
3. Krider, E. Philip (January 2006). "Benjamin Franklin and Lightning Rods". Physics Today. http://www.physicstoday.org/vol-59/iss-1/p42.html. Retrieved on 2008-04-06.
4. J. J. Lowke (1992). "Theory of electrical breakdown in air". Journal of Physics D: Applied Physics 25: 202–210. doi:10.1088/0022-3727/25/2/012. http://www.iop.org/EJ/article/0022-3727/25/2/012/jd920212.pdf?request-id=XIfZw4zI3BGDoxCz2wi7Kg.
5. Kassebaum, J. H. and Kocken, R. A. (1995). "Controlling Static Electricity in Hazardous (Classified) Locations". Petroleum and Chemical Industry 42nd Annual Conference Papers: 105–113. http://ieeexplore.ieee.org/iel3/4013/11530/00523945.pdf?tp=&arnumber=523945&isnumber=11530.
6. Wagner, John P.; Clavijo, Fernando Rangel [doi:10.1016/S0304-3886(00)00019-X Electrostatic charge generation during impeller mixing of used transformer oil] Department of Nuclear Engineering, Safety Engineering and Industrial Hygiene Program, Texas A&M University, College Station, online 21 August 2000; accessed Jan 2009
7. Hearn, Graham (1998). "Static electricity: concern in the pharmaceutical industry?". Pharmaceutical Science & Technology Today 1 (7): 286–287. doi:10.1016/S1461-5347(98)00078-9.
8. Egorov, V.N. Electrification of petroleum fuels Khimiya i Tekhnologiya Topliv i Masel, No. 4, pp. 20–25, April, 1970 accessed Dec 2008
9. Chevron Corporation Aviation Fuels Technical Review 2006, accessed Dec 2008
10. Hearn, Graham Static electricity - guidance for Plant Engineers - Wolfson Electrostatics University of Southampton 2002; accessed Dec 2008
11. Kinzing, G.E., 'Electrostatic Effects in Pneumatic Transport: Assessment, Magnitudes and Future Direction', Journal Pipelines, 4, 95-102, 1984
12. "Snopes.com: Fuelish Pleasures". http://www.snopes.com/autos/hazards/gasvapor.asp. Retrieved on 2008-04-19.
13. "NASA - Crackling Planets". http://science.nasa.gov/headlines/y2005/10aug_crackling.htm. Retrieved on 2008-01-20.
14. "Kids science projects". http://www.creativekidsathome.com/science/staticelectricity.html. Retrieved on 2008-01-20.
15. H. Yasuro, H. Makoto and I. Isao (2007). "Charging of Adhesive Tapes on Peeling". Journal of the Adhesion Society of Japan 43 (3): 97–103. http://sciencelinks.jp/j-east/article/200706/000020070607A0223458.php.
16. "3M Material Safety Data Sheet". http://multimedia.mmm.com/mws/mediawebserver?BBBBBBXeXgc1ZGXFEqZswKKgRmpBWHcbKGcByi5--. Retrieved on 2008-01-20.

Static Electricity - 4

Electronic Components
Many semiconductor devices used in electronics are extremely sensitive to the presence of static electricity and can be damaged by a static discharge.

Static Build-up in Flowing Flammable and Ignitable Materials
Discharge of static electricity can create severe hazards in those industries dealing with flammable substances, where a small electrical spark may ignite explosive mixtures. The flowing movement of finely powdered substances or low conductivity fluids in pipes or through mechanical agitation can build up static electricity. Dust clouds of finely powdered substances can become combustible or explosive. When there is a static discharge in a dust or vapor cloud, explosions have occurred. Major industrial incidents occurred at a grain silo in southwest France, a paint plant in Thailand, and a factory making fiberglass mouldings in Canada.

The ability of a fluid to retain an electrostatic charge depends on its electrical conductivity. When low conductivity fluids flow through pipelines or are mechanically agitated, contact-induced charge separation called flow electrification occurs. Fluids that have low electrical conductivity (below 50 pico siemens/m), are called accumulators. Fluids having conductivities above 50 pico siemens/m are called non-accumulators. In non-accumulators, charges recombine as fast as they are separated and hence electrostatic charge accumulation is not significant. In the petrochemical industry, 50 pico siemens/m is the recommended minimum value of electrical conductivity for adequate removal of charge from a fluid.

Kerosines may have conductivity ranging from <1 pico siemens/m to 20 pico siemens/m. For comparison, deionized water has a conductivity of about 10,000,000 pico siemens/m.
An important concept for insulating fluids is the static relaxation time. This is similar to the time constant (tau) within an RC circuit. For insulating materials, it is the ratio of the static dielectric constant divided by the electrical conductivity of the material. For hydrocarbon fluids, dividing the number 18 by the electrical conductivity of the fluid sometimes approximates this. Thus a fluid that has an electrical conductivity of 1 pico siemens /m will have an estimated relaxation time of about 18 seconds. The excess charge within a fluid will be almost completely dissipated after 4 to 5 times the relaxation time, or 90 seconds for the fluid in the above example.

Charge generation increases at higher fluid velocities and larger pipe diameters, becoming quite significant in pipes 8 inches (200 mm) or larger. Limiting fluid velocity best controls static charge generation in these systems. The British standard BS PD CLC/TR 50404:2003 (formerly BS-5958-Part 2) Code of Practice for Control of Undesirable Static Electricity prescribes pipe flow velocity limits. Because water content has a large impact on the fluids dielectric constant, the recommended velocity for hydrocarbon fluids containing water should be limited to 1 meter/second.

Bonding and earthing are the usual ways by which charge buildup can be prevented. For fluids with electrical conductivity below 10 pico siemens/m, bonding and earthing are not adequate for charge dissipation, and anti-static additives may be required.

References:

1. http://en.wikipedia.org
2. "Franklin's Kite". http://www.mos.org/sln/toe/kite.html. Retrieved on 2008-02-19.
3. Krider, E. Philip (January 2006). "Benjamin Franklin and Lightning Rods". Physics Today. http://www.physicstoday.org/vol-59/iss-1/p42.html. Retrieved on 2008-04-06.
4. J. J. Lowke (1992). "Theory of electrical breakdown in air". Journal of Physics D: Applied Physics 25: 202–210. doi:10.1088/0022-3727/25/2/012. http://www.iop.org/EJ/article/0022-3727/25/2/012/jd920212.pdf?request-id=XIfZw4zI3BGDoxCz2wi7Kg.
5. Kassebaum, J. H. and Kocken, R. A. (1995). "Controlling Static Electricity in Hazardous (Classified) Locations". Petroleum and Chemical Industry 42nd Annual Conference Papers: 105–113. http://ieeexplore.ieee.org/iel3/4013/11530/00523945.pdf?tp=&arnumber=523945&isnumber=11530.
6. Wagner, John P.; Clavijo, Fernando Rangel [doi:10.1016/S0304-3886(00)00019-X Electrostatic charge generation during impeller mixing of used transformer oil] Department of Nuclear Engineering, Safety Engineering and Industrial Hygiene Program, Texas A&M University, College Station, online 21 August 2000; accessed Jan 2009
7. Hearn, Graham (1998). "Static electricity: concern in the pharmaceutical industry?". Pharmaceutical Science & Technology Today 1 (7): 286–287. doi:10.1016/S1461-5347(98)00078-9.
8. Egorov, V.N. Electrification of petroleum fuels Khimiya i Tekhnologiya Topliv i Masel, No. 4, pp. 20–25, April, 1970 accessed Dec 2008
9. Chevron Corporation Aviation Fuels Technical Review 2006, accessed Dec 2008
10. Hearn, Graham Static electricity - guidance for Plant Engineers - Wolfson Electrostatics University of Southampton 2002; accessed Dec 2008
11. Kinzing, G.E., 'Electrostatic Effects in Pneumatic Transport: Assessment, Magnitudes and Future Direction', Journal Pipelines, 4, 95-102, 1984
12. "Snopes.com: Fuelish Pleasures". http://www.snopes.com/autos/hazards/gasvapor.asp. Retrieved on 2008-04-19.
13. "NASA - Crackling Planets". http://science.nasa.gov/headlines/y2005/10aug_crackling.htm. Retrieved on 2008-01-20.
14. "Kids science projects". http://www.creativekidsathome.com/science/staticelectricity.html. Retrieved on 2008-01-20.
15. H. Yasuro, H. Makoto and I. Isao (2007). "Charging of Adhesive Tapes on Peeling". Journal of the Adhesion Society of Japan 43 (3): 97–103. http://sciencelinks.jp/j-east/article/200706/000020070607A0223458.php.
16. "3M Material Safety Data Sheet". http://multimedia.mmm.com/mws/mediawebserver?BBBBBBXeXgc1ZGXFEqZswKKgRmpBWHcbKGcByi5--. Retrieved on 2008-01-20.

Static Electricity - 3

Lightning

Natural static discharge

Lightning is a dramatic natural example of static discharge. While the details are unclear and remain the subject of debate, the initial charge separation is thought to be associated with contact between ice particles within storm clouds. In general, significant charge accumulations can only persist in regions of low electrical conductivity (very few charges free to move in the surroundings), hence the flow of neutralizing charges often results from neutral atoms and molecules in the air being torn apart to form separate positive and negative charges which then travel in opposite directions as an electric current, neutralizing the original accumulation of charge. The static charge in air typically breaks down in this way at around 30,000 volts-per-centimeter (30 kV/cm) depending on humidity. The discharge superheats the surrounding air causing the bright flash, and produces a shockwave causing the clicking sound. The lightning bolt is simply a scaled up version of the sparks seen in more domestic occurrences of static discharge. The flash occurs because the air in the discharge channel is heated to such a high temperature that it emits light by incandescence. The clap of thunder is the result of the shock wave created as the superheated air expands explosively.

References:

1. http://en.wikipedia.org
2. "Franklin's Kite". http://www.mos.org/sln/toe/kite.html. Retrieved on 2008-02-19.
3. Krider, E. Philip (January 2006). "Benjamin Franklin and Lightning Rods". Physics Today. http://www.physicstoday.org/vol-59/iss-1/p42.html. Retrieved on 2008-04-06.
4. J. J. Lowke (1992). "Theory of electrical breakdown in air". Journal of Physics D: Applied Physics 25: 202–210. doi:10.1088/0022-3727/25/2/012. http://www.iop.org/EJ/article/0022-3727/25/2/012/jd920212.pdf?request-id=XIfZw4zI3BGDoxCz2wi7Kg.
5. Kassebaum, J. H. and Kocken, R. A. (1995). "Controlling Static Electricity in Hazardous (Classified) Locations". Petroleum and Chemical Industry 42nd Annual Conference Papers: 105–113. http://ieeexplore.ieee.org/iel3/4013/11530/00523945.pdf?tp=&arnumber=523945&isnumber=11530.
6. Wagner, John P.; Clavijo, Fernando Rangel [doi:10.1016/S0304-3886(00)00019-X Electrostatic charge generation during impeller mixing of used transformer oil] Department of Nuclear Engineering, Safety Engineering and Industrial Hygiene Program, Texas A&M University, College Station, online 21 August 2000; accessed Jan 2009
7. Hearn, Graham (1998). "Static electricity: concern in the pharmaceutical industry?". Pharmaceutical Science & Technology Today 1 (7): 286–287. doi:10.1016/S1461-5347(98)00078-9.
8. Egorov, V.N. Electrification of petroleum fuels Khimiya i Tekhnologiya Topliv i Masel, No. 4, pp. 20–25, April, 1970 accessed Dec 2008
9. Chevron Corporation Aviation Fuels Technical Review 2006, accessed Dec 2008
10. Hearn, Graham Static electricity - guidance for Plant Engineers - Wolfson Electrostatics University of Southampton 2002; accessed Dec 2008
11. Kinzing, G.E., 'Electrostatic Effects in Pneumatic Transport: Assessment, Magnitudes and Future Direction', Journal Pipelines, 4, 95-102, 1984
12. "Snopes.com: Fuelish Pleasures". http://www.snopes.com/autos/hazards/gasvapor.asp. Retrieved on 2008-04-19.
13. "NASA - Crackling Planets". http://science.nasa.gov/headlines/y2005/10aug_crackling.htm. Retrieved on 2008-01-20.
14. "Kids science projects". http://www.creativekidsathome.com/science/staticelectricity.html. Retrieved on 2008-01-20.
15. H. Yasuro, H. Makoto and I. Isao (2007). "Charging of Adhesive Tapes on Peeling". Journal of the Adhesion Society of Japan 43 (3): 97–103. http://sciencelinks.jp/j-east/article/200706/000020070607A0223458.php.
16. "3M Material Safety Data Sheet". http://multimedia.mmm.com/mws/mediawebserver?BBBBBBXeXgc1ZGXFEqZswKKgRmpBWHcbKGcByi5--. Retrieved on 2008-01-20.

Static Electricity - 2

Pressure-induced charge separation
Applied mechanical stress generates a separation of charge in certain types of crystals and ceramics molecules.

Heat-induced charge separation
Heating generates a separation of charge in the atoms or molecules of certain materials. All pyroelectric materials are also piezoelectric. The atomic or molecular properties of heat and pressure response are closely related.

Charge-induced charge separation
A charged object brought into the vicinity of an electrically neutral object will cause a separation of charge within the conductor. Charges of the same polarity are repelled and charges of the opposite polarity are attracted. As the force due to the interaction of electric charges falls off rapidly with increasing distance, the effect of the closer (opposite polarity) charges is greater and the two objects feel a force of attraction. The effect is most pronounced when the neutral object is an electrical conductor as the charges are more free to move around. Careful grounding of part of an object with a charge-induced charge separation can permanently add or remove electrons, leaving the object with a global, permanent charge. This process is integral to the workings of the Van de Graaf Generator, a device commonly used to demonstrate the effects of static electricity.

Static discharge
The spark associated with static electricity is caused by electrostatic discharge, or simply static discharge, as excess charge is neutralized by a flow of charges from or to the surroundings. The feeling of a static electric shock is caused by the stimulation of nerves as the neutralizing current flows through the human body. Due to the ubiquitous presence of water in places inhabited by people, the accumulated charge is generally not enough to cause a dangerously high current.

Despite the apparently innocuous nature of static electricity as we generally experience it, there can be significant risks associated with it in circumstances where large charges may accumulate in the presence of sensitive materials or devices.


References:

1. http://en.wikipedia.org
2. "Franklin's Kite". http://www.mos.org/sln/toe/kite.html. Retrieved on 2008-02-19.
3. Krider, E. Philip (January 2006). "Benjamin Franklin and Lightning Rods". Physics Today. http://www.physicstoday.org/vol-59/iss-1/p42.html. Retrieved on 2008-04-06.
4. J. J. Lowke (1992). "Theory of electrical breakdown in air". Journal of Physics D: Applied Physics 25: 202–210. doi:10.1088/0022-3727/25/2/012. http://www.iop.org/EJ/article/0022-3727/25/2/012/jd920212.pdf?request-id=XIfZw4zI3BGDoxCz2wi7Kg.
5. Kassebaum, J. H. and Kocken, R. A. (1995). "Controlling Static Electricity in Hazardous (Classified) Locations". Petroleum and Chemical Industry 42nd Annual Conference Papers: 105–113. http://ieeexplore.ieee.org/iel3/4013/11530/00523945.pdf?tp=&arnumber=523945&isnumber=11530.
6. Wagner, John P.; Clavijo, Fernando Rangel [doi:10.1016/S0304-3886(00)00019-X Electrostatic charge generation during impeller mixing of used transformer oil] Department of Nuclear Engineering, Safety Engineering and Industrial Hygiene Program, Texas A&M University, College Station, online 21 August 2000; accessed Jan 2009
7. Hearn, Graham (1998). "Static electricity: concern in the pharmaceutical industry?” Pharmaceutical Science & Technology Today 1 (7): 286–287. doi:10.1016/S1461-5347(98)00078-9.
8. Egorov, V.N. Electrification of petroleum fuels Khimiya i Tekhnologiya Topliv i Masel, No. 4, pp. 20–25, April, 1970 accessed Dec 2008
9. Chevron Corporation Aviation Fuels Technical Review 2006, accessed Dec 2008
10. Hearn, Graham Static electricity - guidance for Plant Engineers - Wolfson Electrostatics University of Southampton 2002; accessed Dec 2008
11. Kinzing, G.E., 'Electrostatic Effects in Pneumatic Transport: Assessment, Magnitudes and Future Direction', Journal Pipelines, 4, 95-102, 1984
12. "Snopes.com: Fuelish Pleasures". http://www.snopes.com/autos/hazards/gasvapor.asp. Retrieved on 2008-04-19.
13. "NASA - Crackling Planets". http://science.nasa.gov/headlines/y2005/10aug_crackling.htm. Retrieved on 2008-01-20.
14. "Kids science projects". http://www.creativekidsathome.com/science/staticelectricity.html. Retrieved on 2008-01-20.
15. H. Yasuro, H. Makoto and I. Isao (2007). "Charging of Adhesive Tapes on Peeling". Journal of the Adhesion Society of Japan 43 (3): 97–103. http://sciencelinks.jp/j-east/article/200706/000020070607A0223458.php.
16. "3M Material Safety Data Sheet". http://multimedia.mmm.com/mws/mediawebserver?BBBBBBXeXgc1ZGXFEqZswKKgRmpBWHcbKGcByi5--. Retrieved on 2008-01-20.

Static Electricity 1

Contact with the slide has left the hair positively charged
so that the individual hairs repel one another.

Static electricity refers to the buildup of electric charge on the surface of objects. The static charges remains on an object until they either bleed off to ground or are quickly neutralized by a discharge. Although charge exchange can happen whenever any two surfaces come into contact and separate, a static charge will only remain when at least one of the surfaces has a high resistance to electrical flow (an electrical insulator). The effects of static electricity are familiar to most people because we can see, feel and even hear the spark as the excess charge is neutralized when brought close to a large electrical conductor (for example a path to ground), or a region with an excess charge of the opposite polarity (positive or negative). The familiar phenomenon of a static 'shock' is caused by the neutralization of charge.

History

A simple demonstration using a charged rod to attract scraps of paper.
From the 1878 book Opfindelsernes Bog (Book of inventions), by André Lütken.

The natural phenomenon of static electricity was known at least as early as the 6th century BC, as attested by Thales of Miletus. Scientific research into the subject began when machines were built to create it artificially, such as the friction generator developed by Otto von Guericke in the 17th century. Benjamin Franklin famously demonstrated the connection between static electricity and storm clouds in 1750. In 1832, Michael Faraday published the results of his experiment on the identity of electricities, which proved that the electricity induced using a magnet, voltaic electricity produced by a battery, and static electricity were all the same. Since Faraday's result, the history of static electricity merged with the study of electricity in general.

Causes of static electricity
The materials we observe and interact with from day-to-day are formed from atoms and molecules that are electrically neutral, having an equal number of positive charges (protons, in the nucleus) and negative charges (electrons, in shells surrounding the nucleus). The phenomenon of static electricity requires a separation of positive and negative charges.

Contact-induced charge separation
Electrons can be exchanged between materials on contact; materials with weakly bound electrons tend to lose them, while materials with sparsely filled outer shells tend to gain them. This is known as the triboelectric effect and results in one material becoming positively charged and the other negatively charged. The polarity and strength of the charge on a material once they are separated depends on their relative positions in the triboelectric series. The tribo electric effect is the main cause of static electricity as observed in everyday life, and in common high-school science demonstrations involving rubbing different materials together (e.g. fur and an acrylic rod). Contact-induced charge separation causes your hair to stand up and causes static cling.

References:

1. http://en.wikipedia.org
2. "Franklin's Kite". http://www.mos.org/sln/toe/kite.html. Retrieved on 2008-02-19.
3. Krider, E. Philip (January 2006). "Benjamin Franklin and Lightning Rods". Physics Today. http://www.physicstoday.org/vol-59/iss-1/p42.html. Retrieved on 2008-04-06.
4. J. J. Lowke (1992). "Theory of electrical breakdown in air". Journal of Physics D: Applied Physics 25: 202–210. doi:10.1088/0022-3727/25/2/012. http://www.iop.org/EJ/article/0022-3727/25/2/012/jd920212.pdf?request-id=XIfZw4zI3BGDoxCz2wi7Kg.
5. Kassebaum, J. H. and Kocken, R. A. (1995). "Controlling Static Electricity in Hazardous (Classified) Locations". Petroleum and Chemical Industry 42nd Annual Conference Papers: 105–113. http://ieeexplore.ieee.org/iel3/4013/11530/00523945.pdf?tp=&arnumber=523945&isnumber=11530.
6. Wagner, John P.; Clavijo, Fernando Rangel [doi:10.1016/S0304-3886(00)00019-X Electrostatic charge generation during impeller mixing of used transformer oil] Department of Nuclear Engineering, Safety Engineering and Industrial Hygiene Program, Texas A&M University, College Station, online 21 August 2000; accessed Jan 2009
7. Hearn, Graham (1998). "Static electricity: concern in the pharmaceutical industry?". Pharmaceutical Science & Technology Today 1 (7): 286–287. doi:10.1016/S1461-5347(98)00078-9.
8. Egorov, V.N. Electrification of petroleum fuels Khimiya i Tekhnologiya Topliv i Masel, No. 4, pp. 20–25, April, 1970 accessed Dec 2008
9. Chevron Corporation Aviation Fuels Technical Review 2006, accessed Dec 2008
10. Hearn, Graham Static electricity - guidance for Plant Engineers - Wolfson Electrostatics University of Southampton 2002; accessed Dec 2008
11. Kinzing, G.E., 'Electrostatic Effects in Pneumatic Transport: Assessment, Magnitudes and Future Direction', Journal Pipelines, 4, 95-102, 1984
12. "Snopes.com: Fuelish Pleasures". http://www.snopes.com/autos/hazards/gasvapor.asp. Retrieved on 2008-04-19.
13. "NASA - Crackling Planets". http://science.nasa.gov/headlines/y2005/10aug_crackling.htm. Retrieved on 2008-01-20.
14. "Kids science projects". http://www.creativekidsathome.com/science/staticelectricity.html. Retrieved on 2008-01-20.
15. H. Yasuro, H. Makoto and I. Isao (2007). "Charging of Adhesive Tapes on Peeling". Journal of the Adhesion Society of Japan 43 (3): 97–103. http://sciencelinks.jp/j-east/article/200706/000020070607A0223458.php.
16. "3M Material Safety Data Sheet". http://multimedia.mmm.com/mws/mediawebserver?BBBBBBXeXgc1ZGXFEqZswKKgRmpBWHcbKGcByi5--. Retrieved on 2008-01-20.

Electric Shock 4

Deliberate uses
Electroconvulsive therapy

1. Electric shock is also used as a medical therapy, under carefully controlled conditions:
2. Electroconvulsive therapy or ECT is a psychiatric therapy for mental illness. The objective of the therapy is to induce a seizure for theraputic effect. There is no sensation of shock because the patient is anesthetized. The therapy was originally conceived of after it was observed that depressed patients who also suffered from epilepsy experienced some remission after a spontaneous seizure. The first attempts at deliberately inducing seizure as therapy used not electricity but chemicals; however electricity provided finer control for delivering the minimum stimulus needed. Ideally some other method of inducing seizure would be used, as the electricity may be associated with some of the negative side effects of ECT including amnesia. ECT is generally administered three times a week for about 8-12 treatments.
3. As a treatment for fibrillation or irregular heart rhythms: see defibrillator and cardioversion.
4. As a method of pain relief: see Transcutaneous Electrical Nerve Stimulator (more commonly referred to as a TENS unit).
5. As an aversive punishment for conditioning of mentally handicapped patients with severe behavioral issues. This method is highly controversial and is employed at only one institution in the United States, the Judge Rotenberg Educational Center. The institute also uses electric shock punishments on non-handicapped children with behavioral problems. Whether this constitutes legitimate medical treatment versus abusive discipline is the subject of ongoing litigation.

Torture
Electric shocks have been used as a method of torture, since the received voltage and amperage can be controlled with precision and used to cause pain while avoiding obvious evidence on the victim's body. Such torture usually uses electrodes attached to parts of the victim's body. Another method of electrical torture is stunning with an electroshock gun such as a cattle prod or a taser (provided a sufficiently high voltage and non-lethal current is used in the former case). The Nazis are known to have used electrical torture during World War II. An extensive fictional depiction of such torture is included in the 1966 book The Secret of Santa Vittoria by Robert Crichton. During the Vietnam War, electric shock torture is said to have been used by both the Americans and Vietnamese. A scene of electrical torture in the American Deep South is included in the 1980 Robert Redford film Brubaker. Amnesty International published an official statement that Russian military forces in Chechnya tortured local women with electric shocks by connecting electric wires to their bra straps. Examples in popular modern culture are the electric torture of Martin Riggs in Lethal Weapon and John Rambo in Rambo: First Blood Part II. Japanese serial killer Futoshi Matsunaga used electric shocks for controlling his victims. Advocates for the mentally ill and some psychiatrists such as Thomas Szasz have asserted that electroconvulsive therapy is torture when used without a bona fide medical benefit against recalcitrant or non-responsive patients. See above for ECT as medical therapy. These same arguments and oppositions apply to the use of extremely painful shocks as punishment for behavior modification, a practice that is openly used only at the Judge Rotenberg Institute.

Capital punishment
Electric shock delivered by an electric chair is sometimes used as an official means of capital punishment in the United States, although its use has become rare in recent times. Although the electric chair was at one time considered a more humane and modern execution method than hanging, shooting, poison gassing, the guillotine, etc., it has now been replaced in countries which practice capital punishment by lethal injections. Modern reporting has claimed that it sometimes takes several shocks to be lethal, and that the condemned person may actually catch fire before the process is complete. The brain is always severely damaged and inactivated. Other than in parts of the United States, only the Philippines reportedly has used this method, and only for a few years. It remains a legal means of execution in a few states of the USA.

References:

1. http://en.wikipedia.org
2. http://hypertextbook.com/facts/2000/JackHsu.shtml
3. http://www.grandin.com/humane/elec.stun.html
4. "Industry Backs IEEE-NFPA Arc Flash Testing Program With Initial Donations Of $1.25 Million". IEEE. 14 July 2006. http://standards.ieee.org/announcements/pr_FINArc.html. Retrieved on 2008-01-01.
5. "Publication No. 98-131: Worker Deaths by Electrocution". National Institute for Occupational Safety and Health. http://www.cdc.gov/niosh/docs/98-131/overview.html. Retrieved on 2008-08-16.
6. Philippe Morel, "Line Maintenance Reaches New Heights", Transmission & Distribution World, Aug 1, 1999, accessed 2007-06-22
7. Folliot, Dominigue (1998). "Electricity: Physiological Effects". Encyclopaedia of Occupational Health and Safety, Fourth Edition. http://www.ilo.org/encyclopedia/?doc&nd=857100207&nh=0. Retrieved on 2006-09-04.
8. NIOSH (1998) Worker Death by Electrocution Cincinnati: National Institute for Occupational Safety and Health, NIOSH Pub. No. 98-131.
9. "Torture, American style: The surprising force behind torture: democracies". Boston Globe. 2007-12-16. http://www.boston.com/bostonglobe/ideas/articles/2007/12/16/torture_american_style/. Retrieved on 2008-01-01.
10. Russian Federation Preliminary briefing to the UN Committee against Torture 1 April 2006, statement by Amnesty International
11. "Serial killer's death sentence upheld". Asahi Shimbun. 2007-09-27. http://www.asahi.com/english/Herald-asahi/TKY200709270058.html. Retrieved on 21 March 2008.
12. Death Penalty Information Center

Electric Shock 3

Avoiding danger of shock
It is strongly recommended that people should not work on exposed live conductors if at all possible. If this is not possible then insulated gloves and tools should be used. If both hands make contact with surfaces or objects at different voltages, current can flow through the body from one hand to the other. This can lead the current through the heart. Similarly, if the current is from one hand to the feet, significant current will probably flow through the heart. An alternative to using insulated tools is to isolate the operator from ground, so that there is no conductive path from the live conductor, through the operator's body, to ground. This method is used for working on live high-voltage overhead power lines. It is possible to have a voltage potential between neutral wires and the ground in the event of an improperly wired (disconnected) neutral, or if it is part of certain obsolete (and now illegal) switch circuits. The electrical appliance or lighting equipment might provide some voltage drop, but not nearly enough to avoid a shock. "Live" neutral wires should be treated with the same respect as live wires. Also, the neutral wire must be insulated to the same degree as the live wire to avoid a short circuit. It should be mentioned that much care needs to be taken with electrical systems on ships and boats, especially steel or aluminum ones. Anyone standing on a metal deck or leaning against a bulkhead is automatically grounded, so great care must be taken that all live electrical wires are well insulated. As an example of the danger, during WWII, the battleship USS Washington had not one casualty due to enemy action. However, there were some sailors killed by electrocution while doing such things as using electric drills that had defects in them. For the details, see the official history of this USN warship.

Electrical codes in many parts of the world call for installing a residual-current device (RCD or GFI, ground fault interrupter) in electrical circuits thought to pose a particular hazard to reduce the risk of electrocution. In the USA, for example, a new or remodeled residential dwelling must have them installed in all kitchens, bathrooms, laundry rooms, garages, and also any other room with an unfinished concrete floor* such as a workshop. These devices work by detecting an imbalance between the live and neutral wires. In other words, if more current exits through the live wire than is returning though its neutral wire (presumably via ground), it assumes something is wrong and breaks the circuit in a tiny fraction of a second. There is some concern that these devices might not be fast enough to protect infants and small children in rare instances.
Concrete contains a residual amount of water that makes it somewhat electrically conductive. Also, concrete in contact with any source of water or moisture will absorb some, and the water in concrete always contains dissolved minerals that make the water significantly conductive.
The plumbing system in a home or other small building has historically used metal pipes and thus been connected to ground through the pipes*. This is no longer always true because of the extensive use of plastic piping in recent years, but a plastic system cannot be relied upon for safety purposes. Contrary to popular belief, pure water is not a good conductor of electricity. However, most water is not pure and contains enough dissolved particles (salts) to greatly enhance its conductivity. When the human skin becomes wet, it allows much more current than the dry human body would. Thus, being in the bath or shower will not only ground oneself to return path of the power mains, but lower the body's resistance as well. Under these circumstances, touching any metal switch or appliance that is connected to the power mains could result in severe electric shock or electrocution. While such an appliance is not supposed to be live on its outer metal switch or frame, it may have become so if a defective live bare wire is accidentally touching it (either directly or indirectly via internal metal parts). It is for this reason that mains electrical sockets are prohibited in bathrooms in the United Kingdom. However, the widespread use of plastic cases for everyday appliances, grounding of these appliances, and mandatory installation of Residual Current Devices (R.C.D.s) have greatly reduced this type of electrocution over the recent past decades.

Connecting electrical neutrals to plumbing is against the electrical codes, at least in the United States of America. This is for several reasons. One of these is that connecting any electrical lines to plumbing presents a danger to plumbers or anyone else working on or around plumbing. Also, with metallic plumbing, even small amounts of electric current through them over a significant length of time can cause corrosion to the pipes, the removal of their zinc linings - if they have any, and the breakdown of the solder in their joints.

The ground wire (grounding conductor) of the system is allowed to be connected to plumbing. However as previously stated, the neutral (grounded conductor) is not allowed to be connected. NEC 250.52 Grounding Electrodes (A) Electrodes Permitted for Grounding (1) Metal Underground Water Pipe. This requires: a metal underground water pipe in direct contact with the earth for 3.0m (10ft) or more and electrically continuous to the points of connection of the grounding electrode conductor and the bonding conductor.

A properly grounded appliance greatly reduces the electric shock potential by causing a short circuit if any portion of the metal frame (chassis) is accidentally touching the live wire. This will cause the circuit breaker to turn off or the fuse to blow resulting in a power outage in that area of the home or building. Often there will be a large "bang" and possibly smoke which could easily scare anyone nearby. However, this is still much safer than risking electric shock, since the chance of an out-of-control fire is remote. Where live circuits must be frequently worked on (e.g. television repair), an isolation transformer is sometimes used. Unlike ordinary transformers which raise or lower voltage, the coil windings of an isolation transformer are at a 1:1 ratio, which keeps the voltage unchanged. The purpose is to isolate the neutral wire so that it has no connection to ground. Thus, if a technician accidentally touches the live chassis and ground at the same time, nothing would happen. Neither ground fault interrupters (RCD/GFI) nor isolation transformers can prevent electrocution between the live and neutral wires. This is the same path used by functional electrical appliances, so protection is not possible. However, most accidental electrocutions, especially those not involving electrical work and repair, are via ground -- not the neutral wire.

Electrocution statistics
There were 550 electrocutions in the US in 1993, which translates to 2.1 deaths per million inhabitants. At that time, the incidence of electrocutions was decreasing. Electrocutions in the workplace make up the majority of these fatalities. From 1980–1992, an average of 411 workers were killed each year by electrocution.


References:

1. http://en.wikipedia.org
2. http://hypertextbook.com/facts/2000/JackHsu.shtml
3. http://www.grandin.com/humane/elec.stun.html
4. "Industry Backs IEEE-NFPA Arc Flash Testing Program With Initial Donations Of $1.25 Million". IEEE. 14 July 2006. http://standards.ieee.org/announcements/pr_FINArc.html. Retrieved on 2008-01-01.
5. "Publication No. 98-131: Worker Deaths by Electrocution". National Institute for Occupational Safety and Health. http://www.cdc.gov/niosh/docs/98-131/overview.html. Retrieved on 2008-08-16.
6. Philippe Morel, "Line Maintenance Reaches New Heights", Transmission & Distribution World, Aug 1, 1999, accessed 2007-06-22
7. Folliot, Dominigue (1998). "Electricity: Physiological Effects". Encyclopaedia of Occupational Health and Safety, Fourth Edition. http://www.ilo.org/encyclopedia/?doc&nd=857100207&nh=0. Retrieved on 2006-09-04.
8. NIOSH (1998) Worker Death by Electrocution Cincinnati: National Institute for Occupational Safety and Health, NIOSH Pub. No. 98-131.
9. "Torture, American style: The surprising force behind torture: democracies". Boston Globe. 2007-12-16. http://www.boston.com/bostonglobe/ideas/articles/2007/12/16/torture_american_style/. Retrieved on 2008-01-01.
10. Russian Federation Preliminary briefing to the UN Committee against Torture 1 April 2006, statement by Amnesty International
11. "Serial killer's death sentence upheld". Asahi Shimbun. 2007-09-27. http://www.asahi.com/english/Herald-asahi/TKY200709270058.html. Retrieved on 21 March 2008.
12. Death Penalty Information Center

Electric Shock 2

Arc-flash hazards
Approximately 80% of all injuries and fatalities caused by electrical incidents are not caused by electric shock, but by the intense heat, light, and pressure wave (blast) caused by electrical faults. The arc flash in an electrical fault produces the same type of light radiation from which electric welders protect themselves using face shields with dark glass, heavy leather gloves, and full-coverage clothing. The heat produced may cause severe burns, especially on unprotected flesh. The blast produced by vaporizing metallic components can break bones and irreparably damage internal organs. The degree of hazard present at a particular location can be determined by a detailed analysis of the electrical system, and appropriate protection worn if the electrical work must be performed with the electricity on.

Issues affecting lethality
Other issues affecting lethality are frequency, which is an issue in causing cardiac arrest or muscular spasms, and pathway—if the current passes through the chest or head there is an increased chance of death. From a main circuit or power distribution panel the damage is more likely to be internal, leading to cardiac arrest.

The comparison between the dangers of alternating current and direct current has been a subject of debate ever since the War of Currents in the 1880s. DC tends to cause continuous muscular contractions that make the victim hold on to a live conductor, thereby increasing the risk of deep tissue burns. On the other hand, mains-magnitude AC tends to interfere more with the heart's electrical pacemaker, leading to an increased risk of fibrillation. AC at higher frequencies holds a different mixture of hazards, such as RF burns and the possibility of tissue damage with no immediate sensation of pain. Generally, higher frequency AC current tends to run along the skin rather than penetrating and touching vital organs such as the heart. While there will be severe burn damage at higher voltages, it is normally not fatal.

It is sometimes suggested that human lethality is most common with alternating current at 100–250 volts; however, death has occurred outside this range, with supplies as low as 32 volts and supplies at over 250 volts frequently causing fatalities. Electrical discharge from lightning tends to travel over the surface of the body causing burns and may cause respiratory arrest.

Skin Resistance
The voltage necessary for electrocution depends on the current through the body and the duration of the current. Using Ohm's law, Voltage = Current × Resistance, we see that the current drawn depends on the resistance of the body. The resistance of our skin varies from person to person and fluctuates between different times of day. In general, dry skin is a poor conductor that may have a resistance of around 100,000 Ω, while broken or wet skin may have a resistance of around 1,000 Ω.

Point of entry

1. Macroshock: Current across intact skin and through the body. Current from arm to arm, or between an arm and a foot, is likely to traverse the heart, therefore it is much more dangerous than current between a leg and the ground.
2. Microshock: Direct current path to the heart tissue.

References:

1. http://en.wikipedia.org
2. http://hypertextbook.com/facts/2000/JackHsu.shtml
3. http://www.grandin.com/humane/elec.stun.html
4. "Industry Backs IEEE-NFPA Arc Flash Testing Program With Initial Donations Of $1.25 Million". IEEE. 14 July 2006. http://standards.ieee.org/announcements/pr_FINArc.html. Retrieved on 2008-01-01.
5. "Publication No. 98-131: Worker Deaths by Electrocution". National Institute for Occupational Safety and Health. http://www.cdc.gov/niosh/docs/98-131/overview.html. Retrieved on 2008-08-16.
6. Philippe Morel, "Line Maintenance Reaches New Heights", Transmission & Distribution World, Aug 1, 1999, accessed 2007-06-22
7. Folliot, Dominigue (1998). "Electricity: Physiological Effects". Encyclopaedia of Occupational Health and Safety, Fourth Edition. http://www.ilo.org/encyclopedia/?doc&nd=857100207&nh=0. Retrieved on 2006-09-04.
8. NIOSH (1998) Worker Death by Electrocution Cincinnati: National Institute for Occupational Safety and Health, NIOSH Pub. No. 98-131.
9. "Torture, American style: The surprising force behind torture: democracies". Boston Globe. 2007-12-16. http://www.boston.com/bostonglobe/ideas/articles/2007/12/16/torture_american_style/. Retrieved on 2008-01-01.
10. Russian Federation Preliminary briefing to the UN Committee against Torture 1 April 2006, statement by Amnesty International
11. "Serial killer's death sentence upheld". Asahi Shimbun. 2007-09-27. http://www.asahi.com/english/Herald-asahi/TKY200709270058.html. Retrieved on 21 March 2008.
12. Death Penalty Information Center

Electric Shock

An electric shock can occur upon contact of a human's body with any source of voltage high enough to cause sufficient current through the muscles or hair. The minimum current a human can feel is thought to be about 1 milliampere (mA). The current may cause tissue damage or fibrillation if it is sufficiently high. Death caused by an electric shock is referred to as electrocution. Generally, currents approaching 100 mA are lethal if they pass through sensitive portions of the body.

Shock effects
Psychological
The perception of electric shock can be different depending on the voltage, duration, current, path taken, frequency, etc. Current entering the hand has a threshold of perception of about 5 to 10 mA (milliampere) for DC and about 1 to 10 mA for AC at 60 Hz. Shock perception declines with increasing frequency, ultimately disappearing at frequencies above 15-20 kHz.

Burns
Heating due to resistance can cause extensive and deep burns. Voltage levels of 500 to 1000 volts tend to cause internal burns due to the large energy (which is proportional to the duration multiplied by the square of the voltage) available from the source. Damage due to current is through tissue heating. In some cases 16 volts might be fatal to a human being when the electricity passes through organs such as the heart.

Ventricular fibrillation
A low-voltage (110 to 220 V), 50 or 60-Hz AC current through the chest for a fraction of a second may induce ventricular fibrillation at currents as low as 60 mA. With DC, 300 to 500 mA is required. If the current has a direct pathway to the heart (e.g., via a cardiac catheter or other kind of electrode), a much lower current of less than 1 mA, (AC or DC) can cause fibrillation. If not immediately treated by defibrillation, fibrillations are usually lethal because all the heart muscle cells move independently. Above 200 mA, muscle contractions are so strong that the heart muscles cannot move at all.

Neurological effects
Current can cause interference with nervous control, especially over the heart and lungs. Repeated or severe electric shock which does not lead to death has been shown to cause neuropathy.

When the current path is through the head, it appears that, with sufficient current, loss of consciousness almost always occurs swiftly. (This is borne out by some limited self-experimentation by early designers of the electric chair and by research from the field of animal husbandry, where electric stunning has been extensively studied).

Arc-flash hazards
Approximately 80% of all injuries and fatalities caused by electrical incidents are not caused by electric shock, but by the intense heat, light, and pressure wave (blast) caused by electrical faults. The arc flash in an electrical fault produces the same type of light radiation from which electric welders protect themselves using face shields with dark glass, heavy leather gloves, and full-coverage clothing. The heat produced may cause severe burns, especially on unprotected flesh. The blast produced by vaporizing metallic components can break bones and irreparably damage internal organs. The degree of hazard present at a particular location can be determined by a detailed analysis of the electrical system, and appropriate protection worn if the electrical work must be performed with the electricity on.


References:

1. http://en.wikipedia.org
2. http://hypertextbook.com/facts/2000/JackHsu.shtml
3. http://www.grandin.com/humane/elec.stun.html
4. "Industry Backs IEEE-NFPA Arc Flash Testing Program With Initial Donations Of $1.25 Million". IEEE. 14 July 2006. http://standards.ieee.org/announcements/pr_FINArc.html. Retrieved on 2008-01-01.
5. "Publication No. 98-131: Worker Deaths by Electrocution". National Institute for Occupational Safety and Health. http://www.cdc.gov/niosh/docs/98-131/overview.html. Retrieved on 2008-08-16.
6. Philippe Morel, "Line Maintenance Reaches New Heights", Transmission & Distribution World, Aug 1, 1999, accessed 2007-06-22
7. Folliot, Dominigue (1998). "Electricity: Physiological Effects". Encyclopaedia of Occupational Health and Safety, Fourth Edition. http://www.ilo.org/encyclopedia/?doc&nd=857100207&nh=0. Retrieved on 2006-09-04.
8. NIOSH (1998) Worker Death by Electrocution Cincinnati: National Institute for Occupational Safety and Health, NIOSH Pub. No. 98-131.
9. "Torture, American style: The surprising force behind torture: democracies". Boston Globe. 2007-12-16. http://www.boston.com/bostonglobe/ideas/articles/2007/12/16/torture_american_style/. Retrieved on 2008-01-01.
10. Russian Federation Preliminary briefing to the UN Committee against Torture 1 April 2006, statement by Amnesty International
11. "Serial killer's death sentence upheld". Asahi Shimbun. 2007-09-27. http://www.asahi.com/english/Herald-asahi/TKY200709270058.html. Retrieved on 21 March 2008.
12. Death Penalty Information Center