text:
United States currency/1¢

The United States one-cent coin (penny) is a unit of currency equaling 1/100th of a United States dollar. Its obverse has featured the profile of President Abraham Lincoln since 1909, the centennial of his birth. Since 1959 (the sesquicentennial of Lincoln's birth), the reverse has featured the Lincoln Memorial. The coin is .75 inches (19.05 mm) in diameter and .061 inches (1.55 mm) in thickness.

The one-cent coin is often called a "penny", but the U.S. Mint's official name for this coin is "cent".

1¢ of the United States of America
Value: USD $0.01

 * Mass: 2.5g
 * Diameter: 19.05 mm (0.750in.)
 * Thickness: 1.55mm (0.061in)

 * Edge: Plain
 * Composition: Copper-plated Zinc → 97.5% Zn, 2.5% Cu

 * Years of Minting: 1909-

Obverse
 * Design: Abraham Lincoln
 * Designer: Victor D. Brenner
 * Design Date: 1909

Reverse
 * Design: Lincoln Memorial
 * Designer: Frank Gasparro
 * Design Date: 1959

History of composition

 * 1793–1837 Copper
 * 1837–1857 Bronze (95% copper, 5% tin and zinc)
 * 1857–1864 87.5% copper, 12.5% nickel (also known as NS-12)
 * 1864–1942 Bronze (95% copper, 5% tin and zinc)
 * 1943 Zinc-coated steel
 * 1944–1946 Brass (95% copper, 5% zinc)
 * 1946–1962 Bronze (95% copper, 5% tin and zinc)
 * 1962–1982 Brass (95% copper, 5% zinc)
 * 1982– present 97.5% zinc core, 2.5% copper plating

In 1943, at the peak of World War II, cents of zinc-coated steel were made for a short time due to war demands for copper. A few copper cents from 1943 were produced from the 1942 planchets remaining in the bins. Similarly, some 1944 steel cents have been confirmed. From 1944 through 1946, salvaged ammunition shells made their way into the minting process, and it was not uncommon to see coins featuring streaks of brass or having a considerably darker finish than other issues.

During the early 1970s, the price of copper rose to a point where the cent almost contained more than one cent's worth of copper. This led the Mint to test alternate metals, including aluminum and bronze-clad steel. Aluminum was chosen, and over 1.5 million of these cents were struck and ready for public release before ultimately being rejected. About a dozen aluminum cents are believed to still be in the hands of collectors, although they are now considered illegal, and are subject to seizure by the Secret Service. One aluminum cent was donated to the Smithsonian Institution.

The cent's composition was changed in 1982 because the value of the copper in the coin started to rise above one cent. Some 1982 cents use the 97.5% zinc composition, while others used the 95% copper composition. The price of copper later returned to profitable levels.

"A Penny for Your Thoughts, and 1.4 Cents for the Penny", New York Times, April 22, 2006. Retrieved on May 26, 2007. to produce each cent in addition to the cost of the metal content. Presumably with the rapid rise in price for zinc, the US Mint will have to find another alternative. However, it is Congress that determines the denomination and content of coins that the Mint must produce and put into circulation. As the United States Mint produces only the coins that Congress mandates, it does not have the authority to alter or abolish a unit of currency. If directed to do so by legislation enacted by the Congress and signed by the President, the Treasury Department would again study changing or phasing out the cent. Because the demand exists and the Federal Reserve Banks require inventories to meet the demand, the United States Mint is currently committed to producing the cent at a loss.

Many people can hear the difference between the bronze and copper cents and the newer, zinc cents: simply flip the coin, giving it a good, solid strike. The predominantly copper pennies produce a ringing sound in the 12 kHz range. The zinc coins do not ring.

Designs
The coin has gone through several designs over its 200-year history. Until 1857 it was about the size of the current half-dollar coin.

The following types have been produced:

Flowing Hair Chain
The Chain cent was America's first large cent and the first coin officially produced by the United States Mint. It was struck only during 1793.

Obverse Design
The obverse design consisted of a stylized Liberty head with flowing hair. The inscription "LIBERTY" appeared above the portrait, and the date below. The design was rather sparse and empty compared to those that would come later.

Reverse Design
The reverse's central design figure, for which the coin is named, is an interlocking chain with 15 links, representing the 15 American states in existence at that time. Both the words "ONE CENT" and the fraction "1/100" appear within the chain. Along the outer edge is inscribed "UNITED STATES OF AMERICA". On the first working die, the engraver failed to allow adequate room for the entire inscription, and it had to be abbreviated to "UNITED STATES OF AMERI.". These early dies were cut by hand, rather than being made from master hubs as is the practice today.

Edge
The edge of these coins is decorated with bars and vines with leaves.

Public Reaction
Chain cents were struck during late February and early March 1793; records indicate that approximately 36,103 were produced. However, the public reaction to the coins was largely negative. One newspaper criticized the appearance of the Liberty head, saying that it appeared to be "in a fright". And, while the reverse chain had been intended to symbolise the togetherness of the newly formed Union, many commentators instead interpreted it as representative of slavery. By March, the Mint had run out of planchets, which temporarily halted striking. During this time, a new design – the Wreath cent – was quickly prepared and approved.

Flowing Hair Wreath
The Wreath cent was an American large cent. It was the second design type, following the Chain cent in 1793. It was produced only during that year.

Obverse Design
The obverse design consisted of a stylized Liberty head with flowing hair. The inscription "LIBERTY" appeared above the portrait. Below it was a three-leaved sprig and the date. The design of the Liberty head was modified somewhat from that of the Chain cent to address public criticism.

Reverse Design
The reverse's central design figure, for which the coin is named, was a wreath. The words "ONE CENT" appeared within the wreath, and the corresponding fraction "1/100" appeared beneath it. Along the outer edge was inscribed "UNITED STATES OF AMERICA". A decorative beaded border was added along the rim.

Varieties
Approximately 63,353 Wreath cents were struck. Early specimens featured a stylized "vine/bars" design on the edges of the planchet, which was identical to that of the earlier Chain cent. Later on, this was changed to a lettered edge reading "ONE HUNDRED FOR A DOLLAR". Early American copper collectors generally categorize the coins still further into thirteen different varieties under the Sheldon system. Most of these variations entail relatively minor changes, and often require careful examination to discern. One variety, however, is far more recognizable: the "Strawberry Leaf". On these strikings, the trefoil sprig above the date took the form of a strawberry plant. Only four such specimens are known, and all are heavily circulated. The finest known Strawberry Leaf cent sold at auction for $414,000 in November 2004.

 * Liberty Cap (1793–1796)
 * Draped Bust (1796–1807)
 * Classic Head (1808–1814)
 * Coronet (1816–1839
 * Braided Hair (1839–1857)

Flying Eagle
The Flying Eagle cent is a United States coin that was minted from 1857 to 1858. The coin was designed by James B. Longacre. The Flying Eagle was the first small-sized cent coin minted in the US, replacing the earlier large cent. The obverse of the coin depicts an eagle in flight, a unique subject for the obverse of American coins. The reverse of the coin has the words ONE CENT surrounded by a wreath, similar to the reverse on the later Indian Head cent. The United States Mint in Philadelphia struck between 1000 and 2000 Flying Eagle cents in 1856 as pattern pieces, a way to show influential Congressmen and Senators what these coins would look like. These 1856 Flying Eagle Cents were supposed to have been returned to the Mint and destroyed as they had not been intended for release to the public, but some managed to escape destruction. The 1856 coins are quite rare and valuable. In 1858, there was a "large letter" and "small letter" variety produced, with different punches used to letter "United States of America" on two sets of dies. An easy way to tell the difference between large-letter and small-letter varieties is to look at the word 'America'. In the large letter variety, the letters A and M are joined, whereas in the small letter they are not.

Both the Flying Eagle Cent and Indian Head cents minted from 1859 to 1864 were struck in an alloy of 88% copper and 12% nickel, giving the coins a much whiter sheen than contemporary one-cent pieces. The nickel five-cent coin would not begin production until 1866, and so these nickel-alloy one-cent pieces were slangily known as "nickels".

The early demise of the series was the result of two things. First of all, two high points of the coin were in the same area on each side of the coin, so that when they were struck, it caused a weakness in strike on those points. The second thing was that Longacre could not carve out the dies properly, as he was mostly a painter, not a sculptor.

Indian Head
The Indian Head one-cent coin also known as an Indian Penny was produced by the United States Mint from 1859 to 1909. It was designed by James Barton Longacre, the engraver at the Philadelphia Mint.

The obverse of the coin shows "UNITED STATES OF AMERICA", the head of a Native American wearing a feather head dress, and the year of production. The word "LIBERTY" appears on the band of the head dress. Though not mentioned in the Treasury's modern-day records, the use of "LIBERTY" on the head dress at that time meant the figure was Liberty depicted as a Native American; nearly all regular coins at that time depicted Liberty. The same concept was used nearly 150 years later for the Sacagawea dollar, since there are no known portraits of Sacagawea.

The coin's reverse side shows "ONE CENT" within an oak wreath (a laurel wreath before 1860), with three arrows inserted under the ribbon that binds the two branches of the wreath. Between the ends of the branches is the shield of the United States (which was not in the original design and did not appear on the coin until 1860).

Composition
The coins struck between 1859 and 1864 contained 88% copper and 12% nickel, as required by law. In 1864, the alloy changed to 95% copper and 5% tin and zinc, and the weight of the coins was reduced from 72 grains to 48 grains. (This weight continued for copper-alloy U.S. cents until the 1982 introduction of the current copper-plated zinc cent, which weighs 38.6 grains, or 2.5g, with the exception of 1943.) Research in 1863 had indicated that bronze was an excellent alloy for minor coins, and so the copper-nickel alloy was discontinued. Another possible contributing factor for the alloy change was the whitish color of the early cents, which combined with their size was enough to confuse many merchants into thinking they were dimes, much as more recent cashiers shunned the Susan B. Anthony dollar coin (minted 1979-1981 and again in 1999) for having dimensions and appearance similar to a quarter.

In any event, total production of the Indian Head cent was 1,849,648,000 pieces. The 1909-S had the lowest mintage, only 309,000. It is not considered as scarce as the 1877 issue, (852,500), since fewer of those were kept, particularly in the higher grades.

History
The Director of the Mint, James Ross Snowden, wrote a letter on November 4, 1858, to Secretary of the Treasury Howell Cobb, suggesting that a change be made in the design of the Flying Eagle cent. He pointed out that the relief of that coin was too high, and that the design did not seem too acceptable to the public. Snowden submitted models for a new design, and Secretary Cobb gave his approval to what later became the Indian Head Cent.

According to records at the United States Mint, the design of the Indian Head cent became official on January 1, 1859, and was first released into circulation early that year. When the coin was first produced, Longacre's initials did not appear on the coin, but beginning in 1864, a small "L" was added to the ribbon of the headress, thus making two varieties for that year.

There is a popular rumor about the design of this coin, which states that Mr. Longacre used his daughter Sarah as his model for the Indian likeness on the cent. Unfortunately, this information has not been authenticated in United States Mint files.

Indian Head cents were hoarded during the Civil War, which prompted the minting and usage of Civil War tokens by private merchants and citizens. In response, the metal content of the cent was changed from a copper-nickel alloy to one of almost pure copper in 1864.

Except for a minor design change in 1886 the series continued without major varieties from 1859 to 1909. There is a slight variation in date design in 1873, and a well known overdate (1869 over 68). Most dates are available in lower grades for relatively low cost, and are quite cheap from the 1880s on.

Production
Initially, the production of the five-cent nickel and the one-cent bronze coin was limited by law to the Philadelphia Mint. An Act of Congress passed on April 24, 1906, provided for the making of these denominations at other Mint facilities.

The manufacture of the Indian Head cent at the San Francisco Mint in November 1908 marked the first time this denomination of coins was minted outside of Philadelphia. These San Francisco-minted Indian Head Cents bear the "S" mint mark beneath the ribbon of the wreath on the reverse. One-cent coin production did not begin at the Denver Mint until 1911, during the third year of the Lincoln cent design.

Lincoln Wheat Ears
The Lincoln Wheat Ears Cent (sometimes referred to as a Wheat penny, a Wheatback, a Wheat Head, or a Wheatie) was a United States one-cent coin produced from 1909 to 1958.

Both the obverse and the reverse were designed by Victor David Brenner, a New York sculptor. Brenner's initials, V.D.B., were included on the reverse of the coin below the two stylized wheat stalks on a limited number of the coins until public controversy forced their removal. Brenner's initials were restored to the obverse, below Lincoln's shoulder, in 1918.

One of the more valuable coins to collectors is the 1909 San Francisco, California-minted "VDB" cent, so-named because the designer's initials were included between the stalks of wheat on the lower reverse side; only 484,000 were produced before the public outcry at the designer's initials being so prominently displayed. Even poor-quality examples of the 1909-S VDB coin bring hundreds of dollars and a high-grade mint condition example can sell for $6,000 to $12,000 or more. By contrast, the Philadelphia mint produced nearly 28 million examples of the 1909 VDB cent and such coins are far less valuable. The other key date of the series is the 1914-D, with a mintage of just under 1.2 million. Uncirculated examples have auctioned for over $26,000.

The only other wheat cents to command prices on par with the 1909-S VDB and 1914-D are both error coins: the 1922 "plain" ($5500 for uncirculated specimens), the result of a filled die, and the 1955 doubled die ($1000+ for uncirculated specimens).

In 1959, to commemorate the sesquicentennial of Lincoln's birth, the wheat ears on the reverse of the coin were replaced with a rendering of the Lincoln Memorial by Frank Gasparro.

Specifications
Bronze (1909–1942)
 * Composition: 95% Copper, 5% Tin and Zinc
 * Diameter: 19mm
 * Weight: 3.11g
 * Edge: Plain

Zinc-plated steel (1943)
 * Composition: 100% Steel plated with Zinc
 * Diameter: 19mm
 * Weight: 2.70g
 * Edge: Plain

"Shell casing" Bronze (1944–1945)
 * Composition: 95% Copper and 5% Zinc
 * Diameter: 19mm
 * Weight: 2.70g
 * Edge: Plain

Bronze (1946–1958)
 * Composition: 95% Copper, 5% Tin and Zinc
 * Diameter: 19mm
 * Weight: 3.11g
 * Edge: Plain

Circulation Status
As of 2007, most wheat cents are currently held in private collections and by dealers, often in bulk quantity. However, since the vast majority of wheat cents are only worth ten cents or less, an occasional wheat is still sometimes found in circulation, with a ratio of approximately 1 to 300 cents. This is due to the popularity of bulk coin counting machines such as Coinstar or at a bank, where the wheat cents may had been saved over the years with Lincoln Memorial cents, stored away for sometime, then discovered years later and deposited for cash. An occasional 1943 steel cent is sometimes found in the reject area of a coin counting machine as well.

 * Lincoln Memorial (1959–2008)

Throughout its history, the Lincoln cent has featured several fonts for the date, but most of the digits have been old-style numerals, except with the 4 and 8 neither ascending nor descending. The only significant divergence is that the 3 was non-descending (the same size as a 0, 1, or 2) in the early history, before switching to descending for one year in 1934 and then permanently (as of 2004) in 1943.

The Lincoln Memorial is shown on the reverse of the United States cent. In his treatise Theory and Practise of Numismatic Design, Steve Crooks states that because the Lincoln Memorial is shown in sufficient detail to discern the statue of Lincoln on the reverse of the cent, Abraham Lincoln was the only person to be depicted on both the obverse and reverse of the same United States coin, up until the release of New Jersey state quarter in 1999, which depicts George Washington crossing the Delaware River on the reverse side.

Redesign
In 2009 the cent will get a one-year, four-coin commemorative program marking the 100th anniversary of Lincoln being placed on the cent, and the 200th anniversary of his birth. Thus, 2008 will be the 49th anniversary, and last year that the Lincoln Memorial will be on the U.S penny. This redesign was passed as part of the Presidential $1 Coin Act of 2005, which also mandates that in 2009, numismatic cents will be issued for collectors that have the metallic copper content of cents minted in 1909. In 2010, the cent will be completely redesigned, with a new, permanent design being released into circulation. Lincoln, however, will remain on the coin. The composition for circulating issues will be copper-plated zinc.

Numismatics
Various commentators have suggested that the cent should be eliminated as a unit of currency for several reasons including that many Americans do not actually spend them, but rather only receive them in change at stores and proceed to return them to a bank for higher denomination currencies. Most modern vending machines do not accept cents, further diminishing their utility, and the production cost now exceeds the face value of the coin due to increasing metal prices. In 2001 and 2006, for example, United States Representative Jim Kolbe (R) of Arizona introduced bills which would have stopped production of cents (in 2001 the Legal Tender Modernization Act, and in 2006 the Currency Overhaul for an Industrious Nation (COIN) Act).

As of December 14, 2007, the price of copper is $2.9177 per pound and zinc is $1.0529 per pound. At these prices, the pre-1982 copper cent contains 1.9313 us cents which is a 1.9313 premium face value cents worth of copper zinc alloy, which makes them an attractive target for melting by people wanting to sell the metal at a profit. However, the United States Mint, in anticipation of this practice, implemented new regulations on December 14, 2006 which criminalize the melting of cents and nickels and place limits on export of the coins. Violators can be punished with a fine of up to 10 000 USD and/or imprisoned for a maximum of five years.

In April 2006, the copper-plated zinc cent contains 0.8 cents worth of metal. However, the mint spends about 0.6 cents.

As of February 2, 2008, as of www.kitcometals.com the price of a pound of copper is $3.2634 USD per pound or 7000 grain weight and the price of zinc is $1.1064 USD per pound or 7000 grainweight. At the 2.5 grams per penny cent $0.01 USD token coin, this equals $0.000449660342 USD in copper content of 2.5% of the 2.5 grams total weight and $0.00594553654 USD in zinc content of 97.5% of the 2.5 grams total weight. This totals $0.06639519686 USD metal content per us penny $0.01 token piece which is 0.639519686 or around 64% metal content value for the face value of the 1 US cent coin, these are for coins from 1982 to the present.

For us cent coins 1962 to 1982 is brass (95% copper, 5% zinc) and 1946 to 1962 us pennies cent pieces are bronze 95% copper, 5% tin and zinc which makes them more valuable in metal content than the 1962 to 1982 pieces as tin is on www.metalprices.com at $7.6703 USD per pound of 7000 grain weight where at www.kitcometals.com the price of zinc is $1.1064 USD per pound 7000 grain weight. The 1962 to 1982 brass us penny cent token piece is 2.5*.95 = 2.375 grams or 0.00523597873 pounds * $3.2634 USD per pound 7000 grain weight copper = $0.017087093 USD copper and 2.5*.05 = 0.125 grams or 0.000275577828 pounds * $1.1064 per zinc pound = $0.000304899309 USD zinc content. Therefore $0.017087093 + $0.000304899309 = $0.0173919923 USD per us cent piece 1962 to 1982 or around 74% over face value in metal content.

title: United States currency/1¢


text:
User talk:Top1hit4m

Selam, do you know already about Main Page (since here English is used):
 * If you want to set up a new Wikiversity, you must have ten active participants who are willing to work on that language project. When you have this number you can request (at meta) for a new language domain to be set up. Erkan Yilmaz ( Wikiversity:Chat, wiki blog ) 03:09, 3 February 2008 (UTC)

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/

title: User talk:Top1hit4m


title: User:P858snake


text:
User:MichaelBillington/MWT/Users

Note: This is a list of all MWT users, please do not add your name to this list, as it is done automatically the first time MWT is run
 * 1) MichaelBillington 09:34, 3 February 2008 (UTC)
 * 2) Jordan_Timothy_James_Busson 09:45, 7 August 2008 (UTC)

title: User:MichaelBillington/MWT/Users


text: User:MichaelBillington/MWT

title: User:MichaelBillington/MWT


text:
Friction

What is friction?
Friction is a force, affects motion. Friction acts on materials in contact with another, or acts in different direction in opposite motion.

What does the force of friction depend on?

 * Nature of the materials.
 * How hard the surfaces are pressed together

..such as Rubber vs. Concrete, and not Steel vs. Steel (Rubber vs. Concrete > Steel vs. Steel)

Static Friction :
Friction between the surfaces in contact and which are relatively at rest.
 * Opposes movement of stationary object
 * Moving furniture
 * Hardest part getting moving

Kinetic Friction

 * Acts on objects in motion
 * Once object begins moving, less force to keep in motion
 * Sliding, Rolling, Fluid

Sliding Friction

 * Two objects slide past one another
 * Basketball shoes prevent slipping

Rolling Friction

 * Objects such as wheel or ball rolls across surface
 * Easier to overcome than sliding friction
 * Rolling friction is always less than static friction, as the time period for contact of irregularities between the bodies is less in rolling friction compared to static friction.

Fluid Friction

 * Solid objects move through fluids
 * Cyclists use aerodynamic and spandex to reduce friction
 * Vehicles such as aeroplanes and cars have a special shape known as streamlined shape to reduce windshear or drag.

Air Resistance

 * Friction acting on something moving through air
 * Don't notice unless at high speed.

quiz
{What is ________? It is a force that affects motion and acts on materials in contact with another, or acts in a different direction in opposite motion. + friction - gravity - inertia - tension
 * type="[]"}
 * Correct! Friction is the force that affects motion and acts on materials in contact with another.
 * Incorrect. Gravity is a force that attracts two bodies toward each other.
 * Incorrect. Inertia is the resistance of any physical object to any change in its state of motion.
 * Incorrect. Tension is a force that is exerted equally in opposite directions.

{What does the force of friction depend on? It depends on the ________ of the materials and how hard the surfaces are ________ together. + nature | pressed - weight | pulled - volume | pushed - density | separated
 * type="[]"}
 * Correct! The force of friction depends on the nature of the materials and how hard they are pressed together.
 * Incorrect. Weight is not a direct factor in friction, and pulling is not the action described.
 * Incorrect. Volume is not a direct factor in friction.
 * Incorrect. Density is not a direct factor in friction, and separation decreases friction.

{Which type of friction opposes the movement of a stationary object and is evident when moving furniture? + static friction - kinetic friction - rolling friction - fluid friction
 * type="[]"}
 * Correct! Static friction opposes the movement of stationary objects.
 * Incorrect. Kinetic friction acts on objects in motion.
 * Incorrect. Rolling friction is when an object rolls across a surface.
 * Incorrect. Fluid friction is when solid objects move through fluids.

{Which type of friction is related to basketball shoes preventing slipping? + sliding friction - rolling friction - fluid friction - static friction
 * type="[]"}
 * Correct! Sliding friction occurs when two objects slide past one another.
 * Incorrect. Rolling friction is when an object rolls across a surface.
 * Incorrect. Fluid friction is when solid objects move through fluids.
 * Incorrect. Static friction opposes the movement of stationary objects.

{Which type of friction is always less than static friction due to the short time period for contact of irregularities between the bodies? + rolling friction - sliding friction - fluid friction - kinetic friction
 * type="[]"}
 * Correct! Rolling friction is always less than static friction.
 * Incorrect. Sliding friction occurs when two objects slide past one another.
 * Incorrect. Fluid friction is when solid objects move through fluids.
 * Incorrect. Kinetic friction acts on objects in motion.

{Which type of friction is related to a boy with a helmet on training wheels and cyclists using aerodynamic gear and spandex? + fluid friction - rolling friction - sliding friction - static friction
 * type="[]"}
 * Correct! Fluid friction is when solid objects move through fluids, like air.
 * Incorrect. Rolling friction is when an object rolls across a surface.
 * Incorrect. Sliding friction occurs when two objects slide past one another.
 * Incorrect. Static friction opposes the movement of stationary objects.

{What is the friction called that acts on something moving through air, especially noticeable at high speeds? + air resistance - fluid friction - sliding friction - static friction
 * type="[]"}
 * Correct! Air resistance is the friction acting on something moving through air.
 * Incorrect. While air resistance is a type of fluid friction, the specific term for friction in air is "air resistance".
 * Incorrect. Sliding friction occurs when two objects slide past one another.
 * Incorrect. Static friction opposes the movement of stationary objects.

title: Friction


text:
User talk:Ingenierolo

Welcome here Ingenierolo, if you want you can add info about you on your user page (instead of here). Below more info about Wikiversity, Erkan Yilmaz ( Wikiversity:Chat, wiki blog ) 10:55, 3 February 2008 (UTC)

Welcome
Hello Ingenierolo, and welcome to Wikiversity! If you need help, feel free to visit my talk page, or contact us and ask questions. After you leave a comment on a talk page, remember to sign and date; it helps everyone follow the threads of the discussion. The signature icon in the edit window makes it simple. To get started, you may
 * Take a guided tour and learn to edit;
 * Explore our learning projects;
 * Browse our portals, schools, and research activities;
 * Read and help develop our community policies；or
 * Chat with other Wikiversitans on #wikiversity-en.

And don't forget to explore Wikiversity with the links to your left. Be bold, and see you around Wikiversity! Erkan Yilmaz ( Wikiversity:Chat, wiki blog ) 10:55, 3 February 2008 (UTC)

title: User talk:Ingenierolo


text:
User talk:Rajbetha

Welcome
Hello Rajbetha, and welcome to Wikiversity! If you need help, feel free to visit my talk page, or contact us and ask questions. After you leave a comment on a talk page, remember to sign and date; it helps everyone follow the threads of the discussion. The signature icon in the edit window makes it simple. To get started, you may
 * Take a guided tour and learn to edit;
 * Explore our learning projects;
 * Browse our portals, schools, and research activities;
 * Read and help develop our community policies；or
 * Chat with other Wikiversitans on #wikiversity-en.

And don't forget to explore Wikiversity with the links to your left. Be bold, and see you around Wikiversity! Erkan Yilmaz ( Wikiversity:Chat, wiki blog ) 11:37, 3 February 2008 (UTC)

title: User talk:Rajbetha


text:
User talk:Mdiack

Welcome
Hello Mdiack, and welcome to Wikiversity! If you need help, feel free to visit my talk page, or contact us and ask questions. After you leave a comment on a talk page, remember to sign and date; it helps everyone follow the threads of the discussion. The signature icon in the edit window makes it simple. To get started, you may
 * Take a guided tour and learn to edit;
 * Explore our learning projects;
 * Browse our portals, schools, and research activities;
 * Read and help develop our community policies；or
 * Chat with other Wikiversitans on #wikiversity-en.

And don't forget to explore Wikiversity with the links to your left. Be bold, and see you around Wikiversity! Erkan Yilmaz ( Wikiversity:Chat, wiki blog ) 12:21, 3 February 2008 (UTC)

Another welcome!
Nice to see you here. You can also ask me if you have any questions about WV! --McCormack 12:22, 3 February 2008 (UTC)

title: User talk:Mdiack


text:
User:Maths4

Home work
Answer the following questions

$$4^3\cdots(1)$$

title: User:Maths4


text:
Radio Discussion/Living on Earth/2008.2.1

This show was first broadcast on February 1, 2008. Audio downloads and a transcript are available on this website:
 * http://www.loe.org/shows/shows.htm?programID=08-P13-00005

The links for this week's show were provided by:
 * User:SB_Johnny

Participant feedback will be in Category:Radio Discussions feedback/Living on Earth/2008.2.1


text:
Template:Radio discussions feedback/Living on Earth/2008.1.18/4

usage:


text:
User talk:Msmceg

i am in confucion how to web desinging in wikiversity.please help me

title: User talk:Msmceg


text: Radio Discussion/Living on Earth/2008.1.18/Feedback


text: Talk:Radio Discussion/Living on Earth/2008.1.18/Feedback


text:
User:Erkan Yilmaz/Gathering more info about wikiversity.at

This page will be a copy of my user page from wikiversity.at in case the server there loses the data, I don't want to redo all.

Monday, July 29 2024, (UTC)

=Verlauf der Kontaktaufnahme mit Wikiversity.at=

Ziel

 * Ansprechpartner finden, um mehr Infos über dieses Projekt zu erfahren
 * Zusammenarbeit fördern mit de.wikiversity.org

März 2007 bis jetzt

 * Leider immer noch kein Kontakt (auch schon per mail angefragt mehrmals nach März 2007):
 * siehe auch dazu: Cafeteria in der de.Wikiversity

3. Februar 2008

 * Habe nun:
 * auf die Diskussionsseite der Hauptseite und
 * beim zuletzt aktiven Admin angefragt (auch per email).

 * Auch email geschrieben an:
 * helpdesk AT wikiversity.at (wird im Impressum aufgeführt), die aber prompt mit einem Fehler zurückkam :-( :
 * Delivery to the following recipient failed permanently:
 * Technical details of permanent failure:
 * PERM_FAILURE: SMTP Error (state 13): 550 relay not permitted
 * Mitgeteilt, damit dies behoben werden kann.
 * die email info AT wikiversity.at kam auch mit einem Fehler zurück :-(
 * Mail auch an webmaster AT wikiversity.at (siehe Impressum)
 * die scheint zu existieren, kam noch keine Fehler-Email zurück

 * weitere Möglichkeiten:
 * noch die andren 6 Admins anschreiben
 * Deren Benutzerbeiträge: 8778870, Ajeitler, Cdab, Chefkoch, Dumbo, Kuni, Oehhp, Peter Putzer
 * Habe die 4 Admins, die Mail aktiviert haben, angeschrieben.
 * Ein nicht aktiver Admin hat zurückgeschrieben, ist aber (noch) nicht auf meine bisherigen Fragen eingegangen.
 * Einschreiben an den Betreiber (siehe Impressum oder whois)

=involvierte Wikimedia Projekte=

=Wikiversity.at-Statistiken/-Geschichte=

 * siehe auch: ,
 * Impressum
 * Lizenz GNU FDL

... der anderen Wikiversities
früheste mir bekannte schriftliche Existenz (bitte updaten, wenn ihr was Neueres wisst):

=über mich=

Ich bin Pedell auf der deutschsprachigen Wikiversity.

Außerdem arbeite ich in der IT-Branche im Qualitätsmanagement. Lasse daher hier in der Wikiversity ein bisschen Test-Wissen einfliessen. Hier findet Ihr meinen Blog.

Ich bitte mit Nachdruck, alle meine Artikel in Frage zu stellen, da ich hierdurch mental angesprochen werde. Und insgesamt wird der Artikel auch besser :-)

Du glaubst, du kannst nichts verändern auf der Welt? Dabei ist es so einfach: wenn du jemandem hilfst, kann dies eine Kettenreaktion auslösen. Wenn jeder, der Hilfe erhält, wiederum drei anderen Personen hilft, kannst du etwas/Qualität (nicht nur für Software) in der Welt verändern.

Nur einige Beispiele: Muhammad Yunus hatte eine ganz simple Idee, die die Welt veränderte. Konfuzius (450 v.Chr.): "Sage es mir, und ich vergesse es; zeige es mir, und ich erinnere mich; lass es mich tun, und ich behalte es."

Wir können das auch. Was ist falsch daran, wenn du dich JETZT beteiligst? Trau dich!

=Lernvorgänge=

=TODO=

=Links=


text:
User:BigDunc

My wikipedia user page

title: User:BigDunc


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User:Kasia1986

I am 2nd year student of English at Kazimierz Wielki University.

title: User:Kasia1986


text:
User:Maths5

Hi

$$5+4=9\cdots(1)$$

title: User:Maths5


text:
Materials Science and Engineering/Doctoral review questions/Semiconductor Device Fundamentals

Semiconductors
A semiconductor is a solid material that has electrical conductivity in between that of a conductor and that of an insulator; it can vary over that wide range either permanently or dynamically. Semiconductors are tremendously important in technology. Semiconductor devices, electronic components made of semiconductor materials, are essential in modern electrical devices. Examples range from computers to cellular phones to digital audio players. Silicon is used to create most semiconductors commercially, but dozens of other materials are used as well.

Material Properties
Semiconductors' intrinsic electrical properties are often permanently modified by introducing impurities by a process known as doping. Usually, it is sufficient to approximate that each impurity atom adds one electron or one "hole" (a concept to be discussed later) that may flow freely. Upon the addition of a sufficiently large proportion of impurity dopants, semiconductors will conduct electricity nearly as well as metals. Depending on the kind of impurity, a doped region of semiconductor can have more electrons or holes, and is named N-type or P-type semiconductor material, respectively. Junctions between regions of N- and P-type semiconductors create electric fields, which cause electrons and holes to be available to move away from them, and this effect is critical to semiconductor device operation. Also, a density difference in the amount of impurities produces a small electric field in the region which is used to accelerate non-equilibrium electrons or holes.

In most semiconductors, when electrons lose enough energy to fall from the conduction band to the valence band (the energy levels above and below the band gap), they often emit light, a quantum of energy in the visible electromagnetic spectrum. This photoemission process underlies the light-emitting diode (LED) and the semiconductor laser, both of which are very important commercially. Conversely, semiconductor absorption of light in photodetectors excites electrons to move from the valence band to the higher energy conduction band, thus facilitating detection of light and vary with its intensity. This is useful for fiber optic communications, and providing the basis for energy from solar cells.

Materials
Semiconductors may be elemental materials such as silicon and germanium, or compound semiconductors such as gallium arsenide and indium phosphide, or alloys such as silicon germanium or aluminium gallium arsenide.

Composition
The materials chosen as suitable dopants depend on the atomic properties of both the dopant and the material to be doped. In general, dopants that produce the desired controlled changes are classified as either electron acceptors or donors. A donor atom that activates (that is, becomes incorporated into the crystal lattice) donates weakly-bound valence electrons to the material, creating excess negative charge carriers. These weakly-bound electrons can move about in the crystal lattice relatively freely and can facilitate conduction in the presence of an electric field. (The donor atoms introduce some states under, but very close to the conduction band edge. Electrons at these states can be easily excited to conduction band, becoming free electrons, at room temperature.) Conversely, an activated acceptor produces a hole. Semiconductors doped with donor impurities are called n-type, while those doped with acceptor impurities are known as p-type. The n and p type designations indicate which charge carrier acts as the material's majority carrier. The opposite carrier is called the minority carrier, which exists due to thermal excitation at a much lower concentration compared to the majority carrier.

For example, the pure semiconductor silicon has four valence electrons. In silicon, the most common dopants are IUPAC group 13 (commonly known as group III) and group 15 (commonly known as group V) elements. Group 13 elements all contain three valence electrons, causing them to function as acceptors when used to dope silicon. Group 15 elements have five valence electrons, which allows them to act as a donor. Therefore, a silicon crystal doped with boron creates a p-type semiconductor whereas one doped with phosphorus results in an n-type material.

Purity
Semiconductors with predictable, reliable electronic properties are necessary for mass production. The level of chemical purity needed is extremely high because the presence of impurities even in very small proportions can have large effects on the properties of the material. A high degree of crystalline perfection is also required, since faults in crystal structure (such as dislocations, twins, and stacking faults) interfere with the semiconducting properties of the material. Crystalline faults are a major cause of defective semiconductor devices. The larger the crystal, the more difficult it is to achieve the necessary perfection. Current mass production processes use crystal ingots between four and twelve inches (300 mm) in diameter which are grown as cylinders and sliced into wafers.

Because of the required level of chemical purity and the perfection of the crystal structure which are needed to make semiconductor devices, special methods have been developed to produce the initial semiconductor material. A technique for achieving high purity includes growing the crystal using the Czochralski process. An additional step that can be used to further increase purity is known as zone refining. In zone refining, part of a solid crystal is melted. The impurities tend to concentrate in the melted region, while the desired material recrystalizes leaving the solid material more pure and with fewer crystalline faults.

Electronic Structure
There are three popular ways to describe the electronic structure of a crystal. The first starts from single atoms. An atom has discrete energy levels. When two atoms come close each energy level splits into an upper and a lower level, whereby they delocalize across the two atoms. With more atoms the number of levels increases, and groups of levels form bands. Semiconductors contain many bands. If there is a large distance between the highest occupied state and the lowest unoccupied space, then a gap will likely remain between occupied and unoccupied bands even after band formation.

A second way starts with free electrons waves. When fading in an electrostatic potential due to the cores, due to Bragg reflection some waves are reflected and cannot penetrate the bulk, that is a band gap opens. In this description it is not clear, while the number of electrons fills up exactly all states below the gap.

A third description starts with two atoms. The split states form a covalent bond where two electrons with spin up and spin down are mostly in between the two atoms. Adding more atoms now is supposed not to lead to splitting, but to more bonds. This is the way silicon is typically drawn. The band gap is now formed by lifting one electron from the lower electron level into the upper level. This level is known to be anti-bonding, but bulk silicon has not been seen to lose atoms as easy as electrons are wandering through it. Also this model is most unsuitable to explain how in graded hetero-junction the band gap can vary smoothly.

Czochralski process
The Czochralski process is a method of crystal growth used to obtain single crystals of semiconductors (e.g. silicon, germanium and gallium arsenide), metals (e.g. palladium, platinum, silver, gold), salts and some man made, (or "lab") gemstones.

The most important application may be the growth of large cylindrical ingots, or boules, of single crystal silicon. High-purity, semiconductor-grade silicon (only a few parts per million of impurities) is melted down in a crucible, which is usually made of quartz. Dopant impurity atoms such as boron or phosphorus can be added to the molten intrinsic silicon in precise amounts in order to dope the silicon, thus changing it into n-type or p-type extrinsic silicon. This influences the electrical conductivity of the silicon. A seed crystal, mounted on a rod, is dipped into the molten silicon. The seed crystal's rod is pulled upwards and rotated at the same time. By precisely controlling the temperature gradients, rate of pulling and speed of rotation, it is possible to extract a large, single-crystal, cylindrical ingot from the melt. This process is normally performed in an inert atmosphere, such as argon, and in an inert chamber, such as quartz.

While the largest silicon ingots produced today are 400 mm in diameter and 1 to 2 metres in length, 200 mm and 300 mm diameter crystals are standard industrial processes. Thin silicon wafers are cut from these ingots (typically about 0.2 - 0.75 mm thick) and can be polished to a very high flatness for making integrated circuits, or textured for making solar cells. Other semiconductors, such as gallium arsenide, can also be grown by this method, although lower defect densities in this case can be obtained using variants of the Bridgeman technique.

When silicon is grown by the Czochralski method the melt is contained in a silica (quartz) crucible. During growth the walls of the crucible dissolve into the melt and Czochralski silicon therefore contains oxygen impurities with a typical concentration of 1018cm − 3. Perhaps surprisingly, oxygen impurities can have beneficial effects. Carefully chosen annealing conditions can allow the formation of oxygen precipitates. These have the effect of trapping unwanted transition metal impurities in a process known as gettering. Additionally, oxygen impurities can improve the mechanical strength of silicon wafers by immobilising any dislocations which may be introduced during device processing. It has experimentally been proved in the 1990s that the high oxygen concentration is also beneficial for radiation hardness of silicon particle detectors used in harsh radiation environment ( eg. CERN's LHC/S-LHC projects) Therefore, radiation detectors made of Czochralski- and Magnetic Czochralski-silicon are considered to be promising candidates for many future high-energy physics experiments. However, oxygen impurities can react with boron in an illuminated environment, such as experienced by solar cells. This results in the formation of an electrically active boron–oxygen complex that detracts from cell performance. Module output drops by approximately 3% during the first few hours of light exposure.

Occurrence of unwanted instabilities in the melt can be avoided by investigating and visualizing the temperature and velocity fields during the crystal growth process.

The process is named after Polish scientist Jan Czochralski, who discovered the method in 1916 while investigating the crystallization rates of metals.

Electrons
Electrons have an electric charge of −1.6021765 × 10−19 coulomb, a mass of 9.11 × 10−31 kg based on charge/mass measurements and a relativistic rest mass of about 0.511 MeV/c². The mass of the electron is approximately 1/1836 of the mass of the proton. The common electron symbol is e−.[1] Electron mean lifetime is >4.6x1026 years, see Particle decay.

According to quantum mechanics, electrons can be represented by wavefunctions, from which a calculated probabilistic electron density can be determined. The orbital of each electron in an atom can be described by a wavefunction. Based on the Heisenberg uncertainty principle, the exact momentum and position of the actual electron cannot be simultaneously determined. This is a limitation which, in this instance, simply states that the more accurately we know a particle's position, the less accurately we can know its momentum, and vice versa.

Holes
An electron hole is the conceptual and mathematical opposite of an electron, useful in the study of physics and chemistry. The concept describes the lack of an electron. It is different from the positron, which is the antimatter duplicate of the electron.

The electron hole was introduced into calculations for the following two situations:

 * If an electron is excited into a higher state it leaves a hole in its old state. This meaning is used in Auger electron spectroscopy (and other x-ray techniques), in computational chemistry, and to explain the low electron-electron scattering-rate in crystals (metals, semiconductors).
 * In crystals, band structure calculations lead to an effective mass for the charge carriers, which can be negative. Inspired by the Hall effect, Newton's law is used to attach the negative sign onto the charge.

Effective Mass
In solid state physics, a particle's effective mass is the mass it seems to carry in the semiclassical model of transport in a crystal. It can be shown that, under most conditions, electrons and holes in a crystal respond to electric and magnetic fields almost as if they were free particles in a vacuum, but with a different mass. This mass is usually stated in units of the ordinary mass of an electron me (9.11×10-31 kg).

Definition
When an electron is moving inside a solid material, the force between other atoms will affect its movement and it will not be described by Newton's law. So we introduce the concept of effective mass to describe the movement of electron in Newton's law. The effective mass can be negative or different due to circumstances.

Effective mass is defined by analogy with Newton's second law $$ \vec{F}=m\vec{a} $$. Using quantum mechanics it can be shown that for an electron in an external electric field E:

 * $$ a = {{1} \over {\hbar^2}} \cdot {{d^2 \varepsilon} \over {d k^2}} qE $$

where $$a$$ is acceleration, $$\hbar = h/2\pi$$ is reduced Planck's constant, $$k$$ is the wave number (often called momentum since $$k$$ = $$p/\hbar$$ for free electrons), $$\epsilon(k)$$ is the energy as a function of $$k$$, or the dispersion relation as it is often called. From the external electric field alone, the electron would experience a force of $$\vec{F}=q\vec{E}$$, where q is the charge. Hence under the model that only the external electric field acts, effective mass $$m^*$$ becomes:

 * $$ m^{*} = \hbar^2 \cdot \left[ {{d^2 \varepsilon} \over {d k^2}} \right]^{-1} $$

For a free particle, the dispersion relation is a quadratic, and so the effective mass would be constant (and equal to the real mass). In a crystal, the situation is far more complex. The dispersion relation is not even approximately quadratic, in the large scale. However, wherever a minimum occurs in the dispersion relation, the minimum can be approximated by a quadratic curve in the small region around that minimum. Hence, for electrons which have energy close to a minimum, effective mass is a useful concept.

In energy regions far away from a minimum, effective mass can be negative or even approach infinity. Effective mass, being generally dependent on direction (with respect to the crystal axes), is a tensor. However, for most calculations the various directions can be averaged out.

Effective mass should not be confused with reduced mass, which is a concept from Newtonian mechanics. Effective mass can only be understood with quantum mechanics.

Carrier Numbers in Intrinsic Material
An intrinsic semiconductor, also called an undoped semiconductor or i-type semiconductor, is a pure semiconductor without any significant dopant species present. The number of charge carriers is therefore determined by the properties of the material itself instead of the amount of impurities. In intrinsic semiconductors the number of electrons and the number of holes are equal. n = p.

The conductivity of intrinsic semiconductors can be due to crystal defects or to thermal excitation. In an intrinsic semiconductor the number of electrons in the conduction band is equal to the number of holes in the valence band. An example is Hg0.8Cd0.2>Te at room temperature.

Doping
In semiconductor production, doping refers to the process of intentionally introducing impurities into an extremely pure (also referred to as intrinsic) semiconductor in order to change its electrical properties. The impurities are dependent upon the type of semiconductor. Lightly and moderately doped semiconductors are referred to as extrinsic. A semiconductor which is doped to such high levels that it acts more like a conductor than a semiconductor is called degenerate.

Some dopants are generally added as the (usually silicon) boule is grown, giving each wafer an almost uniform initial doping. To define circuit elements, selected areas (typically controlled by photolithography)[1] are further doped by such processes as diffusion[2] and ion implantation, the latter method being more popular in large production runs due to its better controllability.

The number of dopant atoms needed to create a difference in the ability of a semiconductor to conduct is very small. Where a comparatively small number of dopant atoms are added (of the order of 1 every 100,000,000 atoms) then the doping is said to be low, or light. Where many more are added (of the order of 1 in 10,000) then the doping is referred to as heavy, or high. This is often shown as n+ for n-type dopant or p+ for p-type doping. A more detailed description of the mechanism of doping can be found in the article on semiconductors.

Density of States
In statistical and condensed matter physics, Density of states (DOS) is a property that quantifies how closely packed energy levels are in a quantum-mechanical system. It is usually denoted with one of the symbols g, ρ, n, or N. It is a function g(E) of the internal energy E, such that the expression g(E) dE represents the number of states with energies between E and E+dE. It can also be written as a function of the angular frequency ω, which is proportional to the energy. The density of states is used extensively in condensed-matter physics, where it can refer to electron, photon, or phonon energy levels in a crystalline solid. In crystalline solids, there are often energy ranges where the density of electron states is zero, which means that the electrons cannot be excited to these energies. The density of states also occurs in Fermi's golden rule, which describes how fast quantum-mechanical transitions occur in the presence of a perturbation.

$$g_c(E) = \frac{m_n^* \sqrt{2 m_n^* (E-E_c)}}{\pi^2 \hbar^3}$$

Fermi Function
In statistical mechanics, Fermi-Dirac statistics is a particular case of particle statistics developed by Enrico Fermi and Paul Dirac that determines the statistical distribution of fermions over the energy states for a system in thermal equilibrium. In other words, it is a probability of a given energy level to be occupied by a fermion.

More generally, Fermi-Dirac statistics means that the total wavefunction of fermions must be antisymmetric under an exchange of every pair of fermions (that is, if one exchanges any fermion with another, the wavefunction gets an overall minus sign).

Fermions are particles which are indistinguishable and obey the Pauli exclusion principle, i.e., no more than one particle may occupy the same quantum state at the same time. Fermions have half-integral spin. Statistical thermodynamics is used to describe the behaviour of large numbers of particles. A collection of non-interacting fermions is called a Fermi gas.

$$ n_i = \frac{g_i}{e^{(\epsilon_i-\mu) / k T} + 1} $$

Formulas of n and p
$$n = \int_{E_c}^{E_{top}} g_c(E) f(E) dE$$

$$p = \int_{E_{bottom}}^{E_v} g_v(E)[1 - f(E)] dE$$

$$n = N_C \frac{2}{\sqrt{\pi}} F_{1/2} (\eta_c)$$ $$p = N_V \frac{2}{\sqrt{\pi}} F_{1/2} (\eta_V)$$

$$n = N_C e^{(E_F - E_C)/kT}$$ $$p = N_V e^{(E_V - E_F)/kT}$$

$$n = n_i e^{(E_F - E_i)/kT}$$ $$p = n_i e^{(E_i - E_F)/kT}$$

ni and the np Product
$$n_i = \sqrt{N_C N_V} e^{-E_G/2kT}$$

$$np = n_i^2$$

Charge Neutrality Relationship
$$p -n + N_D^+ - N_A^- = 0$$

With total ionization of dopant atoms:

$$p - n + N_D - N_A = 0\;$$

Carrier Concentration Calculations
$$n = \frac{N_D - N_A}{2} \left ( \left ( \frac{N_D - N_A}{2} \right )^2 + n_i^2 \right )^{1/2}$$

$$p = \frac{n_i^2}{n}$$ $$ \frac{N_A - N_D}{2} \left ( \left ( \frac{N_A - N_D}{2} \right )^2 + n_i^2 \right )^{1/2}$$

Determination of EF
In intrinsic material,

$$n = p\;$$

$$N_C e^{(E_i - E_c)/kT} = N_V e^{(E_v - E_i)/kT}$$

$$E_i = \frac{E_c + E_v}{2} + \frac{kT}{2} \ln \left ( \frac{N_V}{N_C} \right )$$

$$\frac{N_V}{N_C} = \left ( \frac{m_p^*}{m_n^*} \right )^{3/2}$$

$$E_i = \frac{E_c + E_v}{2} + \frac{3}{4} kT \ln \left ( \frac{m_p^*}{m_n^*} \right )$$

$$E_F - E_i = kT \ln (N_D / n_i )\;$$ $$E_i - E_F = kT \ln (N_A / n_i )\;$$

Drift
The mobile charged particles within a conductor move constantly in random directions. In order for a net flow of charge to exist, the particles must also move together with an average drift rate. Electrons are the charge carriers in metals and they follow an erratic path, bouncing from atom to atom, but generally drifting in the direction of the electric field.

$$I_{P|drift} = qpv_dA\;$$ $$\mathbf J_{P|drift} = qp \mathbf v_d$$ $$\mathbf J_{P|drift} = q \mu_p p E$$

Mobility
Units: $$cm^2/V \cdot sec$$

Resistivity
$$E = \rho \mathbf J$$

$$\mathbf J_{drift} = \mathbf J_{N|drift} + \mathbf J_{P|drift}$$ $$\mathbf J_{drift} = q(\mu_n n + \mu_p p) E$$

$$\rho = \frac{1}{q(\mu_n n + \mu_p p)}$$

Band Bending
$$V = - \frac{1}{q} (E_c - E_{ref})$$

$$E = \frac{1}{q} \frac{dE_c}{dx} = \frac{1}{q} \frac{dE_v}{dx} = \frac{1}{q} \frac{dE_i}{dx}$$

Diffusion Current
$$F = - D \nabla \eta$$

$$\mathbf J_{P|diff} = - q D_p \nabla p$$ $$\mathbf J_{N|diff} = - q D_N \nabla n$$

Total Current
$$\mathbf J_P = \mathbf J_{P|drift} + J_{P|diff}$$

$$\mathbf J_P = q \mu_p p E - q D_P \nabla p$$

$$\mathbf J_N = \mathbf J_{N|drift} + J_{N|diff}$$

$$\mathbf J_P = q \mu_n n E - q D_N \nabla n$$

$$\mathbf J = \mathbf J_N \mathbf J_P$$

Einstein Relationship
$$\frac{D_N}{\mu_n} = \frac{kT}{q}$$

Recombination-Generation
Like other solids, semiconductor materials have electronic band structure determined by the crystal properties of the material. The actual energy distribution among the electrons is described by the Fermi energy and the temperature of the electrons. At absolute zero temperature, all of the electrons have energy below the Fermi energy; but at non-zero temperatures the energy levels are randomized and some electrons have energy above the Fermi level.

In semiconductors the Fermi energy lies in the middle of a forbidden band or band gap between two allowed bands called the valence band and the conduction band. The valence band, immediately below the forbidden band, is normally very nearly completely occupied. The conduction band, above the Fermi level, is normally nearly completely empty. Because the valence band is so nearly full, its electrons are not mobile, and cannot flow as electrical current.

However, if an electron in the valence band acquires enough energy to reach the conduction band, it can flow freely among the nearly empty conduction band energy states. Furthermore it will also leave behind an electron hole that can flow as current exactly like a physical charged particle. Carrier generation describes processes by which electrons gain energy and move from the valence band to the conduction band, producing two mobile carriers; while recombination describes processes by which a conduction band electron loses energy and re-occupies the energy state of an electron hole in the valence band.

In a material at thermal equilibrium generation and recombination are balanced, so that the net charge carrier density remains constant. The equilibrium carrier density that results from the balance of these interactions is predicted by thermodynamics. The resulting probability of occupation of energy states in each energy band is given by Fermi-Dirac statistics.

Photogeneration
$$I = I_0 e^{-\alpha x}\;$$

$$\frac{\partial n}{\partial t} |_{\mbox{light}} = \frac{\partial p}{\partial t} |_{\mbox{light}} = G_L(x, \lambda)$$

$$G_L(x, \lambda) = G_{L0}e^{-\alpha x}\;$$

$$\tau_p = \frac{1}{c_p N_T}$$

$$\tau_n = \frac{1}{c_n N_T}$$

$$\frac{\partial p}{\partial t} |_{i-thermal R-G} = - \frac{\Delta p}{\tau_p}$$

Equations of State
$$\frac{\partial n}{\partial t} = \frac{\partial n}{\partial t}|_{drift} + \frac{\partial n}{\partial t}|_{diff} + \frac{\partial n}{\partial t}|_{thermal R-G} + \frac{\partial n}{\partial t}|_{other processes}$$

$$\frac{\partial n}{\partial t} = \frac{1}{q} \nabla \cdot \mathbf J_N \frac{\partial n}{\partial t}|_{thermal R-G} + \frac{\partial n}{\partial t}|_{other processes}$$

Minority Carrier Diffusion Equations
$$\frac{\partial \Delta n_p}{\partial t} = D_N \frac{\partial^2 \Delta n_p}{\partial x^2} - \frac{\Delta n_p}{\tau_n} + G_L$$

Diffusion Lengths
$$L_P = \sqrt{D_P \tau_P}$$

Poisson's Equation
$$\nabla \cdot E = \frac{\rho}{K_S \epsilon_0}$$

If there is a spherically symmetric Gaussian charge density $$ \rho(r) $$:

 * $$ \rho(r) = \frac{Q}{\sigma^3\sqrt{2\pi}^3}\,e^{-r^2/(2\sigma^2)},$$

where Q is the total charge, then the solution φ (r) of Poisson's equation with $$\varepsilon_r = 1$$,

 * $${\nabla}^2 \varphi = - { \rho \over \varepsilon_0 } $$,

is given by

 * $$ \varphi(r) = { 1 \over 4 \pi \varepsilon_0 } \frac{Q}{r}\,\mbox{erf}\left(\frac{r}{\sqrt{2}\sigma}\right)$$.

where erf(x) is the error function. This solution can be checked explicitly by a careful manual evaluation of $${\nabla}^2 \varphi$$. Note that, for r much greater than σ, erf(x) approaches unity and the potential φ (r) approaches the point charge potential $$ { 1 \over 4 \pi \varepsilon_0 } {Q \over r} $$, as one would expect. Furthermore the erf function approaches 1 extremely fast as its argument increase; in practice for r > 3σ the relative error is smaller than 1/1000.

Assume that the dopants are totally ionized
$$\rho = q(p-n+N_D-N_A)\;$$

Built-in Potential
$$V_bi = \frac{kT}{q} \ln \left ( \frac{N_A N_D}{n_i^2} \right )$$

Depletion Width
$$x_n = \left ( \frac{2 K_s \epsilon_0}{q} \frac{N_A}{N_D(N_A +N_D)} V_{bi} \right )^{1/2}$$

$$x_p = \frac{N_D x_n}{N_A}$$

$$W = x_n + x_p = \left ( \frac{2 K_s \epsilon_0}{q} \left ( \frac{N_A + N_D}{N_A N_D} \right ) V_{bi} \right )^{1/2}$$

Depletion Width with Applied Bias
$$x_p = \left ( \frac{2 K_s \epsilon_0}{q} \frac{N_D}{N_A (N_A + N_D)} (V_{bi} - V_A) \right )^{1/2}$$

$$W = \left ( \frac{2 K_s \epsilon_0}{q} \left ( \frac{N_A + N_D}{N_A N_D} \right ) (V_{bi} -V_A) \right )^{1/2}$$


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Action research discussion group

Welcome to the Action research discussion group! You can use this space to discuss or ask questions about anything related to Action research, or make others aware of what kinds of resources there are out there to discuss. Please also add any comments or suggestions about this group - would it be better as a reading group perhaps?

Discussion
"Action research is research the wiki way" - this is a statement I'm interested in exploring. (I've written a journal article on this that will hopefully be published and made freely available soon.) Essentially, my argument comes down to that both action research and wikis are 1) collaborative/participative, 2) iterative (ie continually changing through step-changes), 3) potentially empowering (enabling people to do more than they could have done previously). This is very briefly put - but I'd like to throw it out there to see what other people think. (And please feel free to say you don't know what I'm talking about!) Cormaggio talk 19:59, 3 February 2008 (UTC)

Interested participants

 * Cormaggio (Cormac Lawler) - I'm a PhD student at the University of Manchester, and my PhD is on Developing Wikiversity through action research. I'm very interested in exploring how action research can be used here in Wikiversity - for me, action research is akin to doing research the wiki way - which I've raised for discussion above. Cormaggio talk 19:59, 3 February 2008 (UTC)

title: Action research discussion group


text:
User talk:Aditya2k

Welcome
Hello Aditya2k, and welcome to Wikiversity! If you need help, feel free to visit my talk page, or contact us and ask questions. After you leave a comment on a talk page, remember to sign and date; it helps everyone follow the threads of the discussion. The signature icon in the edit window makes it simple. To get started, you may
 * Take a guided tour and learn to edit;
 * Explore our learning projects;
 * Browse our portals, schools, and research activities;
 * Read and help develop our community policies；or
 * Chat with other Wikiversitans on #wikiversity-en.

And don't forget to explore Wikiversity with the links to your left. Be bold, and see you around Wikiversity! Erkan Yilmaz ( Wikiversity:Chat, wiki blog ) 20:50, 3 February 2008 (UTC)

title: User talk:Aditya2k


text: Category:WMDGS/Has visited Mozambique

title: Category:WMDGS/Has visited Mozambique


text: Category:WMGDS/Does not use condoms currently


text: File:General Purpose Transistors.jpg

title: File:General Purpose Transistors.jpg


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United States currency/5¢

The United States five-cent coin, commonly called a nickel, is a unit of currency equaling one-twentieth, or five hundredths, of a United States dollar.

The nickel's design since 1938 has featured a profile of President Thomas Jefferson on the obverse. From 1938 to 2003, Monticello was featured on the reverse. For 2004 and 2005, nickels featured new designs to commemorate the bicentennials of the Louisiana Purchase and the Lewis and Clark expedition; these new designs were called the Westward Journey nickel series. In 2006, Monticello returned to the reverse, while a new image of Jefferson facing forward was featured on the obverse.

5¢ of the United States

 * Value: 0.05 U.S. dollar

 * Mass: 5.000 g (0.161 troy oz)
 * Diameter: 21.21 mm (0.835 in)
 * Thickness: 1.95 mm (0.077 in)

 * Edge: plain
 * Composition: 75% Cu, 25% Ni

 * "Wartime Nickels"
 * From mid-1942 to 1945
 * 56% Cu, 35% Ag, 9% Mn

 * Years of Minting: 1866–Present, excepting 1922, 1932, and 1933

Obverse

 * Design: Thomas Jefferson
 * Designer: Jamie Franki
 * Design Date: 2006

Reverse

 * Design: Monticello
 * Designer: Felix Schlag
 * Design Date: 1938

General History
Prior to introduction of the nickel, five-cent pieces were very small silver coins called half dimes. Due to shortages of silver during and after the American Civil War, an alternative metal was needed for five-cent coinage, and the copper-nickel alloy still in use today was selected. Numerous problems plagued the coinage of nickels through the middle of the 20th century due to the extreme hardness of the alloy, but modern minting equipment has proven more than adequate for the task.

Nickels have always had a value of one cent per gram (even when special nickel-free versions were issued temporarily during World War II). They were designed as 5 grams in the metric units when they were introduced in 1866, shortly before the Act of July 28, 1866 declared the metric system to be legal for use in the United States.

Applying the term "nickel" to a coin actually precedes the usage of five-cent pieces made from nickel alloy. The term was originally applied to the Indian Head cent coin from 1859–1864 which was composed of copper-nickel. Throughout the Civil War these cents were referred to as "nickels" or "nicks". When the three-cent nickel came onto the scene in 1865, these were the new "nickels" to the common person on the street. In 1866, the Shield nickel hit the spotlight and forever changed the way Americans associated coins made from nickel alloy with a particular denomination.

Local calls placed from public phone booths in the United States cost a nickel in most places until the early 1950s, when the charge was doubled to a dime (10 cents). However, in some places — notably in New Orleans, but mostly in scattered rural areas — the price for such calls remained at a nickel as late as the mid-1970s. This gave rise to the phrase "It's your nickel" in conversations to refer to the prerogative of the person who paid for the phone call to steer the conversation. Cost of a ride on a public transit vehicle — such as a bus or subway — also stood at a nickel during the same period that a pay-phone call carried that charge, in many cities.

Shield Nickel
The Shield nickel, minted from 1866 to 1883, was America's first nickel five-cent piece.

Origin
During the Civil War, gold and silver coinage was hoarded in large quantities. Since all coinage of that era except the cent contained precious metals, this resulted in a shortage of small change, which in turn led to the creation of fractional currency. These low-value paper notes ("shinplasters") were widely disliked, since some merchants refused to accept them and they wore out extremely quickly. Consequently, in 1865, Mint Director James Pollock officially endorsed the creation of a nickel five-cent piece to replace the hated fractional notes. The Mint's chief engraver, James B. Longacre, created a design based on his previous two-cent piece, with a shield as the main obverse motif. On May 16, 1866, legislation enabling the new coin was enacted, and Shield nickels began to be struck that year.

Early History
Since nickel is an extremely hard and brittle metal, it was difficult for the Mint to strike, even in the 25% nickel, 75% copper alloy used for this coin. In fact, it had recently been abandoned for use in the cent for that reason, where it was replaced with a bronze alloy much easier to work with. Its use in coinage was chiefly due to the political influence of nickel magnate Joseph Wharton. The coin's original reverse design had a circle of 13 stars, with rays between each pair of stars. These were removed one year later. Apparently, some individuals complained that the reverse design too closely resembled that of the Confederate flag. Moreover, the high-relief rays exacerbated the coin's inherent striking difficulties. Even when the rays were removed, however, the coins continued to be weakly struck, and the striking dies broke repeatedly.

Replacement
The Shield nickel was quite effective in replacing the half dime, as its base metal composition discouraged hoarding and caused it to circulate very widely. The half dime was thus discontinued in 1873. When Charles E. Barber became the new Chief Engraver, he set about placing his own designs on U.S. coinage, and the Shield nickel was replaced with Barber's Liberty Head nickel in 1883.

Liberty Head V Nickel
The Liberty Head nickel, sometimes referred to as the V nickel due to its reverse design, was an American nickel five-cent piece. Officially, it was minted from 1883 to 1912; a few patterns were struck in 1881 and 1882, and five pieces were surreptitiously struck in 1913, which today number among America's most fabled numismatic rarities. The Liberty Head nickel's composition was the same as that of other U.S. five-cent nickels: 75 percent copper and 25 percent nickel.

Origin
n 1881, Mint Superintendent James Ross Snowden decided to unify the designs of the cent, three-cent nickel, and five-cent nickel. Chief Engraver Charles E. Barber created Liberty Head designs for all three denominations, and patterns were struck later that year. However, Snowden was unable to implement his desired design alterations for the cent and three-cent nickel, so only the five-cent nickel design ever saw full production.

Release
In early 1883, the Liberty Head nickel was first struck for circulation. The first 5.4 million pieces struck contained the Roman numeral V on the reverse, but did not contain the word "CENTS". Con artists quickly noted this, as well as the fact that the coin was roughly the same size as a five-dollar gold coin, and began gold-plating the new nickels and attempting to pass them as gold pieces. According to numismatic legend, one of the perpetrators of this fraud was a deaf-mute named Josh Tatum, whose name is allegedly the origin of the verb "joshing". Supposedly, Tatum was not convicted because, being unable to speak, he did not actually make any fraudulent verbal claims regarding the coins, but merely accepted the change handed to him by the storekeeper. This tale, however, may be apocryphal. Whatever the truth of the case, what is known is that the Mint decided to add the word "CENTS" to the reverse design of the Liberty Head nickel in the middle of the 1883 striking, and this change remained until the coin was discontinued.

Design History
Liberty Head nickels were struck every year from 1883 to 1912. Most were struck at the main U.S. Mint in Philadelphia, but in 1912 the Denver and San Francisco mints also produced the coins. These can be distinguished from the Philadelphia-mint strikes by a small D or S mint mark on the reverse, which is located below the lower left dot. In 1913, the Liberty Head nickel was superseded by James Earle Fraser's new design: the Indian Head (Buffalo) nickel.

1913
The 1913 Liberty Head nickel is one of the best-known and most coveted rarities in American numismatics. In 1972, one specimen became the first coin to command a price of $100,000; in 1996, another specimen would become the first to break the million-dollar barrier. In 2003 one coin was sold for almost $3 million. Only five examples are known to exist: two in museums and three in private collections.

Origin
The Indian Head ("Buffalo") nickel was introduced in February 1913, replacing the Liberty Head design. These were the first official strikings of nickels in 1913; the United States Mint's official records do not record any Liberty Head nickels produced that year. Liberty Head nickels dated 1913 first came to the attention of the numismatic community in 1920. All five were in the possession of Samuel Brown, a numismatist who attended the American Numismatic Association's annual convention and displayed the coins there. Brown had previously placed an advertisement in The Numismatist in December 1919 seeking information on these coins and offering to pay $500 for each. Ostensibly, the coins had been purchased as a result of this offer. However, Samuel Brown had been a Mint employee in 1913, and many numismatic historians have concluded that he was therefore responsible for striking the coins himself and then removing them from the Mint. If true, this would not have been a unique occurrence; such clandestine strikes were actually quite common in the 19th century, with the Class II and III 1804 silver dollars being perhaps the best-known instance. Other numismatic authorities, such as Q. David Bowers, have questioned this scenario, and pointed out that there are several methods by which the coins could have been legitimately produced. Bowers suggests, for instance, that they may have been lawfully issued by the Mint's Medal Department "for cabinet purposes," or that they could be trial pieces struck in late 1912 to test the following year's new coinage dies.

Pedigree
In January 1924, Samuel Brown sold all five 1913 Liberty Head nickels. The intact lot passed through the hands of several other coin dealers before finally being purchased by Colonel E.H.R. Green (son of the infamous miser Hetty Green). Green kept them in his collection until his death in 1936. His estate was then auctioned off, and all five of the 1913 Liberty Head nickels were purchased by two dealers, Eric P. Newman and B.G. Johnson. The dealers broke up the set for the first time.

Eliasberg Specimen
Of the five 1913 Liberty Head nickels, two have proof surfaces, and the other three were produced with standard striking techniques. The finest of the coins has been graded Proof-66 by various professional grading services, including PCGS and NGC.

This coin was purchased from Newman and Johnson by the Numismatic Gallery, a coin dealership that then sold it to famed collector Louis Eliasberg. It remained in Eliasberg's comprehensive collection until after his death. In May 1996, it was sold at an auction conducted by Bowers and Merena, where it was purchased by rarities dealer Jay Parrino for $1,485,000 – the most ever fetched by any single coin up until that point. When it was auctioned again in March 2001, the price climbed to $1,840,000. In May 2005, Legend Numismatics purchased the Eliasberg specimen for $4,150,000. In 2007, the Eliasberg Specimen was sold to an unnamed collector in California for $5 million.

Olsen Specimen
While the Eliasberg specimen is the best preserved of the five coins, the Olsen specimen is almost certainly the most famous. It has been graded Proof-64 by both PCGS and NGC, making it one of only two Proofs (the Eliasberg specimen being the other). The Olsen specimen was featured on an episode of Hawaii Five-O (The $100,000 Nickel, aired on December 11, 1973). It was also briefly owned by Egyptian King Farouk.

When Newman and Johnson broke up the set of five coins, the Olsen specimen was sold first to James Kelly and then to Fred Olson. The latter collector sold the coin to Farouk, but his name has remained attached to it in numismatic circles ever since. In 1972, it was sold to World Wide Coin Investments for $100,000, thus inspiring its title appearance in Hawaii Five-O the following year. The coin's price had doubled, to $200,000, when it was resold to Superior Galleries in 1978. It has been resold on several occasions since then, most recently fetching $3,000,000 in June 2004. The current owner's name has not been disclosed.

Norweb Specimen
The Norweb specimen is one of two 1913 Liberty Head nickels that currently reside in museums. It is currently an exhibit at the Smithsonian Institution.

Newman and Johnson sold the Norweb specimen to F.C.C. Boyd, who then resold it to the Numismatic Gallery (which handled several of the coins over the years). In 1949, it was purchased by King Farouk to replace the Olsen specimen, which he had sold. It remained in Farouk's collection until he was deposed by Gamal Abdel Nasser in 1952. Two years after that, Farouk's possessions were all auctioned off by the new regime. The specimen was once again handled by Numismatic Gallery, and sold this time to Ambassador Henry Norweb and his wife. In 1977, the Norwebs donated the specimen to the Smithsonian, where it remains.

Walton Specimen
The Walton specimen is the most elusive of the five 1913 Liberty Head nickels; for over 40 years, its whereabouts were unknown and it was believed to have been lost. George O. Walton, for whom the specimen is named, purchased it from Newman and Johnson in 1945 for approximately $3,750. On March 9, 1962, Walton died in a car crash en route to a coin show. He had promised the show's promoters that he would exhibit the 1913 Liberty Head nickel there, so it was assumed to have been among the coins in his possession when he died. However, although over a quarter million dollars worth of rare coins were recovered from the crash site, the 1913 Liberty Head nickel was not among them. Some numismatists believed that it had either been lost in the crash or had been taken from the site by an unknown individual. In fact, the coin had not been in the vehicle at all. It remained in the possession of Walton's heirs, but was misidentified as an altered coin. In July 2003, the American Numismatic Association arranged to exhibit the four specimens whose whereabouts were known. A $10,000 reward was offered to anyone who could identify the whereabouts of the fifth coin, with the Bowers and Merena auction house guaranteeing that it would fetch at least $1,000,000 at public auction. After carefully comparing their coin to digital photos of the other specimens, the Walton heirs began to doubt the original verdict that their coin was fake. They brought it to the ANA convention, where expert authenticators examined it at length and determined that it was in fact the genuine Walton specimen. The coin is still held by the Walton heirs.

McDermott Specimen
Currently held by the American Numismatic Association's Money Museum, the McDermott Specimen has the distinction of being the only 1913 Liberty Head nickel to bear marks of circulation. From Johnson and Newman, it was sold to James Kelly, then to J.V. McDermott; it was this latter owner whose name became most prominently attached to the coin's pedigree. McDermott often carried the coin around with him, showing it off to bar patrons and boasting of its extraordinary rarity and value. Due to this activity, the coin lost some of its original mint luster, becoming circulated in condition. Eventually, McDermott protected the coin with a holder to prevent further wear. After McDermott died, the coin was then sold at auction to Aubrey Bebee in 1967 for $46,000. Bebee and his wife donated the coin to the ANA in 1989, where it is exhibited in the Money Museum.

Buffalo Nickel
The Indian Head nickel, also known as the Buffalo nickel, was an American nickel five-cent piece minted from 1913 to 1938. It was designed by sculptor James Earle Fraser.

Design History
The Liberty Head nickel design had been introduced in 1883 by Chief Engraver Charles E. Barber. In the early 1900s, President Theodore Roosevelt had embarked upon a campaign to change the designs of U.S. coinage, most of which had been designed by Barber. Roosevelt considered Barber's coinage ugly and preferred ancient Greek designs, which incorporated high relief. During his administration, Roosevelt had the old double eagle replaced with a new design by Augustus Saint-Gaudens, but most of the minor coinage was not altered. In 1911, Treasury Secretary Franklin MacVeagh, who had worked with Roosevelt in the past and agreed with his opinions on U.S. coinage design, hired James Earle Fraser to design a new nickel.

Fraser featured a profile of a Native American on the obverse of the coin, which was a composite portrait of three Native American chiefs: Iron Tail, Two Moons and John Big Tree. Big Tree's profile was used to create that portion of the portrait from the top of the forehead to the upper lip. (A composite was required because of the federal law that prohibits living individuals from being portrayed on U.S. currency.)

The "buffalo" portrayed on the reverse was an American Bison, possibly Black Diamond, from the Central Park Zoo.

Design Changes
Soon after the Indian Head nickel went into circulation, it became apparent that the reverse design was problematic; the "FIVE CENTS" inscription, which was on a raised mound at the bottom of the reverse, was one of the highest spots on the coin, and thus wore away very quickly. As a result, the design was modified by Charles Barber during its first year of production. Barber removed the raised mound and lowered the relief of the inscription so that it would not wear away as quickly, along with other design changes. However, one problem that was not addressed was the placement of the date. Like "FIVE CENTS" in the original design, the date was placed at a relief that exposed it to a great deal of wear. (A similar problem would later be seen on the Standing Liberty Quarter.) This issue was never definitively addressed by the Mint, so many Indian Head nickels have their dates partially or completely obliterated through extensive circulation.

A more radical, if unofficial, design change for the Indian Head nickel was the advent of the hobo nickel. Enterprising artists would scrape away the original obverse and modify the Native American, his headdress, or the background to create a completely original work of art. Even more ambitious efforts completely eliminated the original design save a few key features (usually the date).

An interesting design variety was produced in 1937 (one year before the production of these nickels was stopped)-the 1937-D "3-Legged" buffalo nickel. The buffalo's right foreleg is gone on this rare error. This was produced when the leg was accidentally ground off in the process of removing marks from the die. In Mint State condition this coin is worth a significant amount of money. Some normal buffalo nickels have had the front leg ground down as an attempt to mimic the more valuable die error, but these can be distinguished by other features present on the "3-Legged" buffalo nickel.

Circulation Status
Most Buffalo nickels were removed from circulation in the 1950s and 1960s in various degrees of wear, although it wasn't uncommon with diligent searching to find one as late as the early 1980s. Today, any talk of a Buffalo Nickel showing up in circulation is notable, as approximately 1 in 25,000 nickels in circulation today is a Buffalo Nickel. Many of these have the date completely worn off.

Mint Marks
Indian Head nickels were minted at the Philadelphia, Denver, and San Francisco Mints and either have a 'D', 'S', or no mint mark on the reverse of the coin below the words FIVE CENTS.

Profile of Jefferson Nickel (1938–2004)
The Jefferson nickel, designed by Felix Schlag in a Mint-sponsored contest, was minted beginning in 1938. (In 1966 his initials were added to the base of the bust.) The obverse features a profile of Thomas Jefferson, while the reverse features his Virginian estate, Monticello. The steps on the building were slightly modified during 1939, but otherwise the design did not change until 2003. All three mints turned out vast quantities of Jefferson nickels until 1954, when San Francisco halted production for 14 years, resuming only from 1968 to 1970, although it still produces proof coins. Since 1970 all nickels for circulation have been minted at Philadelphia and Denver. Mint marks may be found on the reverse, in the right field between Monticello and the rim, on nickels from 1938 to 1964. From 1965 to 1967, no mint marks were used, and beginning in 1968, the mint mark was moved to the obverse, just below the date, where it remains today. In 1980, the Philadelphia mint began using a "P" mint mark on all nickels. This design is by far the most common currently in circulation.

Wartime Nickels
From mid 1942 to 1945, so-called "Wartime" composition nickels were created. These coins are 56% copper, 35% silver and 9% manganese. The only other U.S. coins to use manganese are the Sacagawea and presidential dollars. These coins are usually a bit darker than regular nickels, said to be due to their manganese content (as was true of many British coins minted from 1920 through 1947). However, carefully-protected proof sets of these coins are difficult to tell from the standard alloy. A more likely reason for the darker appearance of the wartime coin was due to exposure to sulfur during circulation, which invariably gave the coins a mild and somewhat distinctive dark silver tarnish.[citation needed]

The wartime nickel features the largest mint mark ever to grace a United States coin, located above Monticello's dome on the reverse. This mark was a large D or S if appropriate for those mints, but nickels of this series minted in Philadelphia have the unique distinction of being the only U.S. coins minted prior to 1979 to bear a P mint mark. There are eleven coins in the regular series (plus a moderately scarce overdate, the 1943/2-P), and they can be purchased in circulated condition at low cost. When the price of silver rose in the 1960s the "war nickels" quickly disappeared from circulation, a process often aided by their distinctive silver-tarnish appearance, which sometimes appeared in banded form from contact of coins with sulfur-containing elastic bands in pockets.

An unofficial variety of the wartime coin dated 1944 was made in 1954 when counterfeit nickels were produced by Francis LeRoy Henning of Erial, New Jersey. He had previously been arrested for counterfeiting $5 bills. The 1944 nickels were quickly spotted since Henning neglected to add the large mintmark. He also made counterfeit nickels dated 1939, 1946, 1947, and possibly 1953 as well as one other unidentified date. It is estimated that more than 100,000 of Henning's nickels reached circulation. These can still be found in pocket change, and there is a thriving collectors' market for them, although owning a counterfeit is technically illegal. Henning dumped another 200,000 nickels in Copper Creek, New Jersey, of which only 14,000 were recovered. Another 200,000 are thought to have been dumped in the Schuylkill River. When caught, Henning was sentenced to 3 years in jail, and was required to pay a $5,000 fine.

As Collectibles
Jefferson nickels are one of the easiest sets of any denomination to collect from circulation. One can still find coins from the 1940s in circulation on occasion. Many Jefferson nickel collectors look for fully struck steps on the image of Monticello. Premiums are paid for coins with five or six full steps. These are fairly rare, even on current issues. Proofs and special mint set coins (1965–1967), as well as matte proofs, exist, and have value above circulating coinage. Specialists look for the number of discernable steps on the façade of Monticello, and those without wear are known as "Full Step" Jefferson Nickels. One of the rarest, or "key dates" of the series is the 1950-D nickel. It has the lowest mintage of all the Jeffersons minted. However, they are not hard to find in higher grades, since it was known by the public from the beginning that the mintage was low, and thus they were hoarded. In uncirculated condition, the 1939-D, 1939-S, and 1942-D are far rarer than the 1950-D and command higher prices than any other coins in the series.

Westward Journey Nickel Series
Throughout the 20th century, Congress allowed the U.S. Mint to make changes to coinage every 25 years without specific authorization. Since the 1990s the government had begun to respond to lobbying in favor of changing coinage design. This led to the State Quarters series and in 2002, a proposal to change 2003 nickels as well. Initial proposals by the Mint had a new obverse based on a portrait by Gilbert Stuart, and a reverse with an American Indian and a bald eagle facing west.

Congressman Eric Cantor (R-Virginia), the Chief Deputy Majority Whip for his party, objected to the lack of consultation with Congress about their proposal, and was particularly concerned that Monticello, located near his district, would not return to the reverse of the nickel in 2006. Some raised the issue that the Mint's proposed new reverse did not relate specifically enough to Lewis & Clark or the Louisiana Purchase, the events that the proposed changes were meant to commemorate. This led to the enactment of Public Law 108-15, the American 5-cent Coin Design Continuity Act, in 2003. This act, originally dubbed the Keep Monticello on the Nickel Act by Cantor, modified the United States Code to require the return to a depiction of Monticello starting in January 2006, and permanently eliminate the Mint's right to change it again without Congressional approval. The delay and controversy meant the Mint ran out of time to change the reverse of the nickel in 2003.

Upon passage of Cantor's new law, the Mint proposed the Westward Journey nickel series. The series consisted of two new reverse designs for 2004 and two for 2005.

2004 Designs
n 2004, the reverse of the nickel changed, with two different designs during the year. The first design, placed into circulation on March 1, 2004, featured a design based upon a rendition of the original Indian Peace Medal commissioned for Lewis and Clark's expedition. It was designed by Norman E. Nemeth.

In the autumn of 2004, the reverse changed again to feature a view of Lewis and Clark's keelboat in full sail that transported members of the Corps of Discovery expedition and their supplies through the rivers of the Louisiana Territory. This design depicts Meriwether Lewis and William Clark in full uniform, standing in the bow of the keelboat. This nickel was designed by Al Maletsky.

2005 Designs
On September 16, 2004, the U.S. Mint unveiled its new designs for 2005. They had been chosen by John W. Snow on July 22, 2004 but were not disclosed to the public. The U.S. Mint revealed that the Felix Schlag depiction of Thomas Jefferson was being done away with in favor of a more modern depiction of Jefferson. The new obverse of the Jefferson nickel was designed by Joe Fitzgerald and engraved by Don Everhart II. Its circulation began on February 28, 2005.

Also unveiled on September 16, 2004 were two new reverses. A depiction of the American bison temporarily returns to the reverse after a 67-year absence. The new reverse was designed by Jamie N. Franki and engraved by Norman E. Nemeth. The U.S. Mint had been lobbied to include the American bison on the nickel in the hope of keeping the public interested in its continuing recovery after nearly being hunted to extinction after the completion of the transcontinental railroad.

The final Westward Journey nickel reverse was designed by Joe Fitzgerald and engraved by Donna Weaver. It depicts the Pacific Ocean and the words from William Clark's diary upon reaching it. In a controversial move, the U.S. Mint decided to amend Clark's actual words. He had originally written, "Ocian in view! O! The Joy!" but as the spelling "ocian" is nonstandard (and might have led to hoarding in the mistaken belief that the Mint had made an error that would soon be corrected), the U.S. Mint decided to modify it to "ocean".

Forward-Facing Jefferson (2006)
In 2006, the nickel returned to using Felix Schlag's Monticello design on a newly cast reverse, while the obverse features a new forward-facing portrait of Jefferson, based on the 1800 Rembrandt Peale painting of Jefferson. It is the first U.S. circulating coin that features the image of a President facing forward. The new obverse was designed by Jamie Franki. The word Liberty is shown in Jefferson's own handwriting, as it was on the 2005 Westward Journey nickels.

Metal Value
As of December 14, 2007 dc, the value of the metal in a United States nickel coin reached 5.5759 cents, a 1.11518 premium over its face value, due to the rising costs of copper and nickel against a falling U.S. Dollar. In an attempt to avoid losing large quantities of circulating nickels to melting, the United States Mint introduced new interim rules on December 14, 2006 criminalizing the melting and export of pennies and nickels. Violators of these rules can be punished with a fine of up to $10,000, five years imprisonment, or both.

Nickels minted from 1942-1945 during World War II contain 1.75 g (0.05626 oz) silver. The silver content of these "war nickels" as of October, 2007 is worth $0.77.

As of February 2, 2008 dc, the value of the metal in United States nickel coin has reached 6.612482746 cents, a 1.22496549 premium over its face value, due to the rising costs of copper and nickel against a falling U.S. Dollar.

--km 23:25, 4 February 2008 (UTC)

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title: United States currency/5¢


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