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23,700 | Like flour mills, factories producing aspirin tablets must control the amount of the powder that becomes airborne inside the building, because the powder-air mixture can be explosive. The National Institute for Occupational Safety and Health (NIOSH) has set a recommended exposure limit in the United States of 5mg/m (ti... | https://en.wikipedia.org/wiki?curid=1525 |
23,701 | The synthesis of aspirin is classified as an esterification reaction. Salicylic acid is treated with acetic anhydride, an acid derivative, causing a chemical reaction that turns salicylic acid's hydroxyl group into an ester group (R-OH → R-OCOCH). This process yields aspirin and acetic acid, which is considered a bypro... | https://en.wikipedia.org/wiki?curid=1525 |
23,702 | Reaction between acetic acid and salicylic acid can also form aspirin but this esterification reaction is reversible and the presence of water can lead to hydrolysis of the aspirin. So, an anhydrous reagent is preferred. | https://en.wikipedia.org/wiki?curid=1525 |
23,703 | Formulations containing high concentrations of aspirin often smell like vinegar because aspirin can decompose through hydrolysis in moist conditions, yielding salicylic and acetic acids. | https://en.wikipedia.org/wiki?curid=1525 |
23,704 | Aspirin, an acetyl derivative of salicylic acid, is a white, crystalline, weakly acidic substance, which melts at , and decomposes around . Its acid dissociation constant (p"K") is 3.5 at . | https://en.wikipedia.org/wiki?curid=1525 |
23,705 | Polymorphism, or the ability of a substance to form more than one crystal structure, is important in the development of pharmaceutical ingredients. Many drugs receive regulatory approval for only a single crystal form or polymorph. For a long time, only one crystal structure for aspirin was known. That aspirin might ha... | https://en.wikipedia.org/wiki?curid=1525 |
23,706 | In 1971, British pharmacologist John Robert Vane, then employed by the Royal College of Surgeons in London, showed aspirin suppressed the production of prostaglandins and thromboxanes. For this discovery he was awarded the 1982 Nobel Prize in Physiology or Medicine, jointly with Sune Bergström and Bengt Ingemar Samuels... | https://en.wikipedia.org/wiki?curid=1525 |
23,707 | Aspirin's ability to suppress the production of prostaglandins and thromboxanes is due to its irreversible inactivation of the cyclooxygenase (COX; officially known as prostaglandin-endoperoxide synthase, PTGS) enzyme required for prostaglandin and thromboxane synthesis. Aspirin acts as an acetylating agent where an ac... | https://en.wikipedia.org/wiki?curid=1525 |
23,708 | Low-dose aspirin use irreversibly blocks the formation of thromboxane A in platelets, producing an inhibitory effect on platelet aggregation during the lifetime of the affected platelet (8–9 days). This antithrombotic property makes aspirin useful for reducing the incidence of heart attacks in people who have had a hea... | https://en.wikipedia.org/wiki?curid=1525 |
23,709 | Prostaglandins, local hormones produced in the body, have diverse effects, including the transmission of pain information to the brain, modulation of the hypothalamic thermostat, and inflammation. Thromboxanes are responsible for the aggregation of platelets that form blood clots. Heart attacks are caused primarily by ... | https://en.wikipedia.org/wiki?curid=1525 |
23,710 | At least two different types of cyclooxygenases, COX-1 and COX-2, are acted on by aspirin. Aspirin irreversibly inhibits COX-1 and modifies the enzymatic activity of COX-2. COX-2 normally produces prostanoids, most of which are proinflammatory. Aspirin-modified PTGS2 (prostaglandin-endoperoxide synthase 2) produces lip... | https://en.wikipedia.org/wiki?curid=1525 |
23,711 | Several COX-2 inhibitors, such as rofecoxib (Vioxx), have been withdrawn from the market, after evidence emerged that PTGS2 inhibitors increase the risk of heart attack and stroke. Endothelial cells lining the microvasculature in the body are proposed to express PTGS2, and, by selectively inhibiting PTGS2, prostaglandi... | https://en.wikipedia.org/wiki?curid=1525 |
23,712 | Furthermore, aspirin, while inhibiting the ability of COX-2 to form pro-inflammatory products such as the prostaglandins, converts this enzyme's activity from a prostaglandin-forming cyclooxygenase to a lipoxygenase-like enzyme: aspirin-treated COX-2 metabolizes a variety of polyunsaturated fatty acids to hydroperoxy p... | https://en.wikipedia.org/wiki?curid=1525 |
23,713 | Aspirin has been shown to have at least three additional modes of action. It uncouples oxidative phosphorylation in cartilaginous (and hepatic) mitochondria, by diffusing from the inner membrane space as a proton carrier back into the mitochondrial matrix, where it ionizes once again to release protons. Aspirin buffers... | https://en.wikipedia.org/wiki?curid=1525 |
23,714 | Aspirin is readily broken down in the body to salicylic acid, which itself has anti-inflammatory, antipyretic, and analgesic effects. In 2012, salicylic acid was found to activate AMP-activated protein kinase, which has been suggested as a possible explanation for some of the effects of both salicylic acid and aspirin.... | https://en.wikipedia.org/wiki?curid=1525 |
23,715 | Acetylsalicylic acid is a weak acid, and very little of it is ionized in the stomach after oral administration. Acetylsalicylic acid is quickly absorbed through the cell membrane in the acidic conditions of the stomach. The increased pH and larger surface area of the small intestine causes aspirin to be absorbed more s... | https://en.wikipedia.org/wiki?curid=1525 |
23,716 | About 50–80% of salicylate in the blood is bound to human serum albumin, while the rest remains in the active, ionized state; protein binding is concentration-dependent. Saturation of binding sites leads to more free salicylate and increased toxicity. The volume of distribution is 0.1–0.2 L/kg. Acidosis increases the v... | https://en.wikipedia.org/wiki?curid=1525 |
23,717 | As much as 80% of therapeutic doses of salicylic acid is metabolized in the liver. Conjugation with glycine forms salicyluric acid, and with glucuronic acid to form two different glucuronide esters. The conjugate with the acetyl group intact is referred to as the "acyl glucuronide"; the deacetylated conjugate is the "p... | https://en.wikipedia.org/wiki?curid=1525 |
23,718 | Salicylates are excreted mainly by the kidneys as salicyluric acid (75%), free salicylic acid (10%), salicylic phenol (10%), and acyl glucuronides (5%), gentisic acid (< 1%), and 2,3-dihydroxybenzoic acid. When small doses (less than 250mg in an adult) are ingested, all pathways proceed by first-order kinetics, with an... | https://en.wikipedia.org/wiki?curid=1525 |
23,719 | Medicines made from willow and other salicylate-rich plants appear in clay tablets from ancient Sumer as well as the Ebers Papyrus from ancient Egypt. Hippocrates referred to the use of salicylic tea to reduce fevers around 400 BC, and willow bark preparations were part of the pharmacopoeia of Western medicine in class... | https://en.wikipedia.org/wiki?curid=1525 |
23,720 | In 1853, chemist Charles Frédéric Gerhardt treated sodium salicylate with acetyl chloride to produce acetylsalicylic acid for the first time; in the second half of the 19th century, other academic chemists established the compound's chemical structure and devised more efficient methods of synthesis. In 1897, scientists... | https://en.wikipedia.org/wiki?curid=1525 |
23,721 | Aspirin's popularity declined after the development of acetaminophen/paracetamol in 1956 and ibuprofen in 1962. In the 1960s and 1970s, John Vane and others discovered the basic mechanism of aspirin's effects, while clinical trials and other studies from the 1960s to the 1980s established aspirin's efficacy as an anti-... | https://en.wikipedia.org/wiki?curid=1525 |
23,722 | Aspirin sales revived considerably in the last decades of the 20th century, and remain strong in the 21st century with widespread use as a preventive treatment for heart attacks and strokes. | https://en.wikipedia.org/wiki?curid=1525 |
23,723 | Bayer lost its trademark for Aspirin in the United States in actions taken between 1918 and 1921 because it had failed to use the name for its own product correctly and had for years allowed the use of "Aspirin" by other manufacturers without defending the intellectual property rights. Today, aspirin is a generic trade... | https://en.wikipedia.org/wiki?curid=1525 |
23,724 | Aspirin is used in the treatment of a number of conditions, including fever, pain, rheumatic fever, and inflammatory conditions, such as rheumatoid arthritis, pericarditis, and Kawasaki disease. Lower doses of aspirin have also been shown to reduce the risk of death from a heart attack, or the risk of stroke in people ... | https://en.wikipedia.org/wiki?curid=1525 |
23,725 | Aspirin is an effective analgesic for acute pain, although it is generally considered inferior to ibuprofen because aspirin is more likely to cause gastrointestinal bleeding. Aspirin is generally ineffective for those pains caused by muscle cramps, bloating, gastric distension, or acute skin irritation. As with other N... | https://en.wikipedia.org/wiki?curid=1525 |
23,726 | Aspirin, either by itself or in a combined formulation, effectively treats certain types of a headache, but its efficacy may be questionable for others. Secondary headaches, meaning those caused by another disorder or trauma, should be promptly treated by a medical provider. Among primary headaches, the International C... | https://en.wikipedia.org/wiki?curid=1525 |
23,727 | Like its ability to control pain, aspirin's ability to control fever is due to its action on the prostaglandin system through its irreversible inhibition of COX. Although aspirin's use as an antipyretic in adults is well established, many medical societies and regulatory agencies, including the American Academy of Fami... | https://en.wikipedia.org/wiki?curid=1525 |
23,728 | Aspirin is used as an anti-inflammatory agent for both acute and long-term inflammation, as well as for treatment of inflammatory diseases, such as rheumatoid arthritis. | https://en.wikipedia.org/wiki?curid=1525 |
23,729 | Aspirin is an important part of the treatment of those who have had a heart attack. It is generally not recommended for routine use by people with no other health problems, including those over the age of 70. | https://en.wikipedia.org/wiki?curid=1525 |
23,730 | The 2009 Antithrombotic Trialists' Collaboration published in Lancet evaluated the efficacy and safety of low dose aspirin in secondary prevention. In those with prior ischaemic stroke or acute myocardial infarction, daily low dose aspirin was associated with a 19% relative risk reduction of serious cardiovascular even... | https://en.wikipedia.org/wiki?curid=1525 |
23,731 | After percutaneous coronary interventions (PCIs), such as the placement of a coronary artery stent, a U.S. Agency for Healthcare Research and Quality guideline recommends that aspirin be taken indefinitely. Frequently, aspirin is combined with an ADP receptor inhibitor, such as clopidogrel, prasugrel, or ticagrelor to ... | https://en.wikipedia.org/wiki?curid=1525 |
23,732 | The status of the use of aspirin for the primary prevention in cardiovascular disease is conflicting and inconsistent, with recent changes from previously recommending it widely decades ago, and that some referenced newer trials in clinical guidelines show less of benefit of adding aspirin alongside other anti-hyperten... | https://en.wikipedia.org/wiki?curid=1525 |
23,733 | As of , the United States Preventive Services Task Force (USPSTF) determined that there was a "small net benefit" for patients aged 40-59 with a 10% or greater 10-year cardiovascular disease (CVD) risk, and "no net benefit" for patients aged over 60. Determining the net benefit was based on balancing the risk reduction... | https://en.wikipedia.org/wiki?curid=1525 |
23,734 | Aspirin may reduce the overall risk of both getting cancer and dying from cancer. There is substantial evidence for lowering the risk of colorectal cancer (CRC), but must be taken for at least 10–20 years to see this benefit. It may also slightly reduce the risk of endometrial cancer, breast cancer, and prostate cancer... | https://en.wikipedia.org/wiki?curid=1525 |
23,735 | Some conclude the benefits are greater than the risks due to bleeding in those at average risk. Others are unclear if the benefits are greater than the risk. Given this uncertainty, the 2007 United States Preventive Services Task Force (USPSTF) guidelines on this topic recommended against the use of aspirin for prevent... | https://en.wikipedia.org/wiki?curid=1525 |
23,736 | A meta-analysis through 2019 said that there was an association between taking aspirin and lower risk of cancer of the colorectum, esophagus, and stomach. | https://en.wikipedia.org/wiki?curid=1525 |
23,737 | In 2021, the U.S. Preventive services Task Force raised questions about the use of aspirin in cancer prevention. It notes the results of the 2018 ASPREE (Aspirin in Reducing Events in the Elderly) Trial, in which the risk of cancer-related death was higher in the aspirin-treated group than in the placebo group. | https://en.wikipedia.org/wiki?curid=1525 |
23,738 | Aspirin, along with several other agents with anti-inflammatory properties, has been repurposed as an add-on treatment for depressive episodes in subjects with bipolar disorder in light of the possible role of inflammation in the pathogenesis of severe mental disorders. However, meta-analytic evidence is based on very ... | https://en.wikipedia.org/wiki?curid=1525 |
23,739 | Although cohort and longitudinal studies have shown low-dose aspirin has a greater likelihood of reducing the incidence of dementia, numerous randomised controlled trials have not validated this. | https://en.wikipedia.org/wiki?curid=1525 |
23,740 | Aspirin is a first-line treatment for the fever and joint-pain symptoms of acute rheumatic fever. The therapy often lasts for one to two weeks, and is rarely indicated for longer periods. After fever and pain have subsided, the aspirin is no longer necessary, since it does not decrease the incidence of heart complicati... | https://en.wikipedia.org/wiki?curid=1525 |
23,741 | Along with rheumatic fever, Kawasaki disease remains one of the few indications for aspirin use in children in spite of a lack of high quality evidence for its effectiveness. | https://en.wikipedia.org/wiki?curid=1525 |
23,742 | Low-dose aspirin supplementation has moderate benefits when used for prevention of pre-eclampsia. This benefit is greater when started in early pregnancy. | https://en.wikipedia.org/wiki?curid=1525 |
23,743 | Aspirin has also demonstrated anti-tumoral effects, via inhibition of the PTTG1 gene, which is often overexpressed in tumors. | https://en.wikipedia.org/wiki?curid=1525 |
23,744 | For some people, aspirin does not have as strong an effect on platelets as for others, an effect known as aspirin-resistance or insensitivity. One study has suggested women are more likely to be resistant than men, and a different, aggregate study of 2,930 people found 28% were resistant. | https://en.wikipedia.org/wiki?curid=1525 |
23,745 | A study in 100 Italian people found, of the apparent 31% aspirin-resistant subjects, only 5% were truly resistant, and the others were noncompliant. | https://en.wikipedia.org/wiki?curid=1525 |
23,746 | Another study of 400 healthy volunteers found no subjects who were truly resistant, but some had "pseudoresistance, reflecting delayed and reduced drug absorption". | https://en.wikipedia.org/wiki?curid=1525 |
23,747 | Meta-analysis and systematic reviews have concluded that laboratory confirmed aspirin resistance confers increased rates of poorer outcomes in cardiovascular and neurovascular diseases. Although the majority of research conducted has surrounded cardiovascular and neurovascular, there is emerging research into the risk ... | https://en.wikipedia.org/wiki?curid=1525 |
23,748 | Adult aspirin tablets are produced in standardised sizes, which vary slightly from country to country, for example 300mg in Britain and 325mg (or 5 grains) in the United States. Smaller doses are based on these standards, "e.g.", 75mg and 81mg tablets. The tablets are commonly called "baby aspirin" or "baby-strength", ... | https://en.wikipedia.org/wiki?curid=1525 |
23,749 | In general, for adults, doses are taken four times a day for fever or arthritis, with doses near the maximal daily dose used historically for the treatment of rheumatic fever. For the prevention of myocardial infarction (MI) in someone with documented or suspected coronary artery disease, much lower doses are taken onc... | https://en.wikipedia.org/wiki?curid=1525 |
23,750 | March 2009 recommendations from the USPSTF on the use of aspirin for the primary prevention of coronary heart disease encourage men aged 45–79 and women aged 55–79 to use aspirin when the potential benefit of a reduction in MI for men or stroke for women outweighs the potential harm of an increase in gastrointestinal h... | https://en.wikipedia.org/wiki?curid=1525 |
23,751 | Low-dose aspirin use was also associated with a trend toward lower risk of cardiovascular events, and lower aspirin doses (75 or 81mg/day) may optimize efficacy and safety for people requiring aspirin for long-term prevention. | https://en.wikipedia.org/wiki?curid=1525 |
23,752 | In children with Kawasaki disease, aspirin is taken at dosages based on body weight, initially four times a day for up to two weeks and then at a lower dose once daily for a further six to eight weeks. | https://en.wikipedia.org/wiki?curid=1525 |
23,753 | In October 2020, the US Food and Drug Administration (FDA) required the drug label to be updated for all nonsteroidal anti-inflammatory medications to describe the risk of kidney problems in unborn babies that result in low amniotic fluid. They recommend avoiding NSAIDs in pregnant women at 20 weeks or later in pregnan... | https://en.wikipedia.org/wiki?curid=1525 |
23,754 | Aspirin should not be taken by people who are allergic to ibuprofen or naproxen, or who have salicylate intolerance or a more generalized drug intolerance to NSAIDs, and caution should be exercised in those with asthma or NSAID-precipitated bronchospasm. Owing to its effect on the stomach lining, manufacturers recommen... | https://en.wikipedia.org/wiki?curid=1525 |
23,755 | Aspirin use has been shown to increase the risk of gastrointestinal bleeding. Although some enteric-coated formulations of aspirin are advertised as being "gentle to the stomach", in one study, enteric coating did not seem to reduce this risk. Combining aspirin with other NSAIDs has also been shown to further increase ... | https://en.wikipedia.org/wiki?curid=1525 |
23,756 | Blockade of COX-1 by aspirin apparently results in the upregulation of COX-2 as part of a gastric defense. Several trials suggest that the simultaneous use of a COX-2 inhibitor with aspirin may increase the risk of gastrointestinal injury. However, currently available evidence has been unable to prove that this effect ... | https://en.wikipedia.org/wiki?curid=1525 |
23,757 | In addition to enteric coating, "buffering" is the other main method companies have used to try to mitigate the problem of gastrointestinal bleeding. Buffering agents are intended to work by preventing the aspirin from concentrating in the walls of the stomach, although the benefits of buffered aspirin are disputed. Al... | https://en.wikipedia.org/wiki?curid=1525 |
23,758 | Taking it with vitamin C has been investigated as a method of protecting the stomach lining. Taking equal doses of vitamin C and aspirin may decrease the amount of stomach damage that occurs compared to taking aspirin alone. | https://en.wikipedia.org/wiki?curid=1525 |
23,759 | It is a widespread habit among eye specialists (ophthalmologists) to prescribe aspirin as an add-on medication for patients with retinal vein occlusion (RVO), such as central retinal vein occlusion (CRVO) and branch retinal vein occlusion (BRVO). The reason of this widespread use is the evidence of its proven effective... | https://en.wikipedia.org/wiki?curid=1525 |
23,760 | However, a large-scale investigation based on data of nearly 700 patients showed "that aspirin or other antiplatelet aggregating agents or anticoagulants adversely influence the visual outcome in patients with CRVO and hemi-CRVO, without any evidence of protective or beneficial effect". Several expert groups, including... | https://en.wikipedia.org/wiki?curid=1525 |
23,761 | Large doses of salicylate, a metabolite of aspirin, cause temporary tinnitus (ringing in the ears) based on experiments in rats, via the action on arachidonic acid and NMDA receptors cascade. | https://en.wikipedia.org/wiki?curid=1525 |
23,762 | Reye's syndrome, a rare but severe illness characterized by acute encephalopathy and fatty liver, can occur when children or adolescents are given aspirin for a fever or other illness or infection. From 1981 to 1997, 1207 cases of Reye's syndrome in people younger than 18 were reported to the US Centers for Disease Con... | https://en.wikipedia.org/wiki?curid=1525 |
23,763 | For a small number of people, taking aspirin can result in symptoms including hives, swelling, and headache. Aspirin can exacerbate symptoms among those with chronic hives, or create acute symptoms of hives. These responses can be due to allergic reactions to aspirin, or more often due to its effect of inhibiting the C... | https://en.wikipedia.org/wiki?curid=1525 |
23,764 | Aspirin and other NSAIDs, such as ibuprofen, may delay the healing of skin wounds. Earlier findings from two small, low-quality trials suggested a benefit with aspirin (alongside compression therapy) on venous leg ulcer healing time and leg ulcer size, however larger, more recent studies of higher quality have been una... | https://en.wikipedia.org/wiki?curid=1525 |
23,765 | Aspirin can induce swelling of skin tissues in some people. In one study, angioedema appeared one to six hours after ingesting aspirin in some of the people. However, when the aspirin was taken alone, it did not cause angioedema in these people; the aspirin had been taken in combination with another NSAID-induced drug ... | https://en.wikipedia.org/wiki?curid=1525 |
23,766 | Aspirin causes an increased risk of cerebral microbleeds having the appearance on MRI scans of 5 to 10mm or smaller, hypointense (dark holes) patches. | https://en.wikipedia.org/wiki?curid=1525 |
23,767 | A study of a group with a mean dosage of aspirin of 270mg per day estimated an average absolute risk increase in intracerebral hemorrhage (ICH) of 12 events per 10,000 persons. In comparison, the estimated absolute risk reduction in myocardial infarction was 137 events per 10,000 persons, and a reduction of 39 events p... | https://en.wikipedia.org/wiki?curid=1525 |
23,768 | Aspirin and other NSAIDs can cause abnormally high blood levels of potassium by inducing a hyporeninemic hypoaldosteronic state via inhibition of prostaglandin synthesis; however, these agents do not typically cause hyperkalemia by themselves in the setting of normal renal function and euvolemic state. | https://en.wikipedia.org/wiki?curid=1525 |
23,769 | Use of low-dose aspirin before a surgical procedure has been associated with an increased risk of bleeding events in some patients, however, ceasing aspirin prior to surgery has also been associated with an increase in major adverse cardiac events. An analysis of multiple studies found a three-fold increase in adverse ... | https://en.wikipedia.org/wiki?curid=1525 |
23,770 | On 9 July 2015, the US Food and Drug Administration (FDA) toughened warnings of increased heart attack and stroke risk associated with nonsteroidal anti-inflammatory drugs (NSAID). Aspirin is an NSAID but is not affected by the new warnings. | https://en.wikipedia.org/wiki?curid=1525 |
23,771 | Aspirin overdose can be acute or chronic. In acute poisoning, a single large dose is taken; in chronic poisoning, higher than normal doses are taken over a period of time. Acute overdose has a mortality rate of 2%. Chronic overdose is more commonly lethal, with a mortality rate of 25%; chronic overdose may be especiall... | https://en.wikipedia.org/wiki?curid=1525 |
23,772 | Aspirin is known to interact with other drugs. For example, acetazolamide and ammonium chloride are known to enhance the intoxicating effect of salicylates, and alcohol also increases the gastrointestinal bleeding associated with these types of drugs. Aspirin is known to displace a number of drugs from protein-binding ... | https://en.wikipedia.org/wiki?curid=1525 |
23,773 | The ISIS-2 trial demonstrated that aspirin at doses of 160mg daily for one month, decreased the mortality by 21% of participants with a suspected myocardial infarction in the first five weeks. A single daily dose of 324mg of aspirin for 12 weeks has a highly protective effect against acute myocardial infarction and dea... | https://en.wikipedia.org/wiki?curid=1525 |
23,774 | Aspirin has been repurposed as an add-on treatment for depressive episodes in subjects with bipolar disorder. However, meta-analytic evidence is based on very few studies and does not suggest any efficacy of aspirin in the treatment of bipolar depression. Thus, notwithstanding the biological rationale, the clinical per... | https://en.wikipedia.org/wiki?curid=1525 |
23,775 | Several studies investigated the anti-infective properties of aspirin for bacterial, viral and parasitic infections. Aspirin was demonstrated to limit platelet activation induced by "Staphylococcus aureus" and "Enterococcus faecalis" and to reduce streptococcal adhesion to heart valves. In patients with tuberculous men... | https://en.wikipedia.org/wiki?curid=1525 |
23,776 | There are a many anecdotal reportings that aspirin can improve plant's growth and resistance though most research involved salicylic acid instead of aspirin. | https://en.wikipedia.org/wiki?curid=1525 |
23,777 | Aspirin is sometimes used in veterinary medicine as an anticoagulant or to relieve pain associated with musculoskeletal inflammation or osteoarthritis. Aspirin should only be given to animals under the direct supervision of a veterinarian, as adverse effects—including gastrointestinal issues—are common. An aspirin over... | https://en.wikipedia.org/wiki?curid=1525 |
23,778 | Dogs are better able to tolerate aspirin than cats are. Cats metabolize aspirin slowly because they lack the glucuronide conjugates that aid in the excretion of aspirin, making it potentially toxic if dosing is not spaced out properly. No clinical signs of toxicosis occurred when cats were given 25mg/kg of aspirin ever... | https://en.wikipedia.org/wiki?curid=1525 |
23,779 | Ohm's law states that the current through a conductor between two points is directly proportional to the voltage across the two points. Introducing the constant of proportionality, the resistance, one arrives at the usual mathematical equation that describes this relationship: | https://en.wikipedia.org/wiki?curid=49090 |
23,780 | where is the current through the conductor, "V" is the voltage measured "across" the conductor and "R" is the resistance of the conductor. More specifically, Ohm's law states that the "R" in this relation is constant, independent of the current. If the resistance is not constant, the previous equation cannot be called ... | https://en.wikipedia.org/wiki?curid=49090 |
23,781 | The law was named after the German physicist Georg Ohm, who, in a treatise published in 1827, described measurements of applied voltage and current through simple electrical circuits containing various lengths of wire. Ohm explained his experimental results by a slightly more complex equation than the modern form above... | https://en.wikipedia.org/wiki?curid=49090 |
23,782 | In physics, the term "Ohm's law" is also used to refer to various generalizations of the law; for example the vector form of the law used in electromagnetics and material science: | https://en.wikipedia.org/wiki?curid=49090 |
23,783 | where J is the current density at a given location in a resistive material, E is the electric field at that location, and "σ" (sigma) is a material-dependent parameter called the conductivity. This reformulation of Ohm's law is due to Gustav Kirchhoff. | https://en.wikipedia.org/wiki?curid=49090 |
23,784 | In January 1781, before Georg Ohm's work, Henry Cavendish experimented with Leyden jars and glass tubes of varying diameter and length filled with salt solution. He measured the current by noting how strong a shock he felt as he completed the circuit with his body. Cavendish wrote that the "velocity" (current) varied d... | https://en.wikipedia.org/wiki?curid=49090 |
23,785 | Francis Ronalds delineated "intensity" (voltage) and "quantity" (current) for the dry pile—a high voltage source—in 1814 using a gold-leaf electrometer. He found for a dry pile that the relationship between the two parameters was not proportional under certain meteorological conditions. | https://en.wikipedia.org/wiki?curid=49090 |
23,786 | Ohm did his work on resistance in the years 1825 and 1826, and published his results in 1827 as the book "Die galvanische Kette, mathematisch bearbeitet" ("The galvanic circuit investigated mathematically"). He drew considerable inspiration from Fourier's work on heat conduction in the theoretical explanation of his wo... | https://en.wikipedia.org/wiki?curid=49090 |
23,787 | where "x" was the reading from the galvanometer, "l" was the length of the test conductor, "a" depended on the thermocouple junction temperature, and "b" was a constant of the entire setup. From this, Ohm determined his law of proportionality and published his results. | https://en.wikipedia.org/wiki?curid=49090 |
23,788 | where formula_5 is the open-circuit emf of the thermocouple, formula_6 is the internal resistance of the thermocouple and formula_7 is the resistance of the test wire. In terms of the length of the wire this becomes, | https://en.wikipedia.org/wiki?curid=49090 |
23,789 | Ohm's law was probably the most important of the early quantitative descriptions of the physics of electricity. We consider it almost obvious today. When Ohm first published his work, this was not the case; critics reacted to his treatment of the subject with hostility. They called his work a "web of naked fancies" and... | https://en.wikipedia.org/wiki?curid=49090 |
23,790 | In the 1850s, Ohm's law was widely known and considered proved. Alternatives such as "Barlow's law", were discredited, in terms of real applications to telegraph system design, as discussed by Samuel F. B. Morse in 1855. | https://en.wikipedia.org/wiki?curid=49090 |
23,791 | The electron was discovered in 1897 by J. J. Thomson, and it was quickly realized that it is the particle (charge carrier) that carries electric currents in electric circuits. In 1900 the first (classical) model of electrical conduction, the Drude model, was proposed by Paul Drude, which finally gave a scientific expla... | https://en.wikipedia.org/wiki?curid=49090 |
23,792 | The development of quantum mechanics in the 1920s modified this picture somewhat, but in modern theories the average drift velocity of electrons can still be shown to be proportional to the electric field, thus deriving Ohm's law. In 1927 Arnold Sommerfeld applied the quantum Fermi-Dirac distribution of electron energi... | https://en.wikipedia.org/wiki?curid=49090 |
23,793 | While the old term for electrical conductance, the mho (the inverse of the resistance unit ohm), is still used, a new name, the siemens, was adopted in 1971, honoring Ernst Werner von Siemens. The siemens is preferred in formal papers. | https://en.wikipedia.org/wiki?curid=49090 |
23,794 | In the 1920s, it was discovered that the current through a practical resistor actually has statistical fluctuations, which depend on temperature, even when voltage and resistance are exactly constant; this fluctuation, now known as Johnson–Nyquist noise, is due to the discrete nature of charge. This thermal effect impl... | https://en.wikipedia.org/wiki?curid=49090 |
23,795 | Ohm's work long preceded Maxwell's equations and any understanding of frequency-dependent effects in AC circuits. Modern developments in electromagnetic theory and circuit theory do not contradict Ohm's law when they are evaluated within the appropriate limits. | https://en.wikipedia.org/wiki?curid=49090 |
23,796 | Ohm's law is an empirical law, a generalization from many experiments that have shown that current is approximately proportional to electric field for most materials. It is less fundamental than Maxwell's equations and is not always obeyed. Any given material will break down under a strong-enough electric field, and so... | https://en.wikipedia.org/wiki?curid=49090 |
23,797 | Ohm's law has been observed on a wide range of length scales. In the early 20th century, it was thought that Ohm's law would fail at the atomic scale, but experiments have not borne out this expectation. As of 2012, researchers have demonstrated that Ohm's law works for silicon wires as small as four atoms wide and one... | https://en.wikipedia.org/wiki?curid=49090 |
23,798 | The dependence of the current density on the applied electric field is essentially quantum mechanical in nature; (see Classical and quantum conductivity.) A qualitative description leading to Ohm's law can be based upon classical mechanics using the Drude model developed by Paul Drude in 1900. | https://en.wikipedia.org/wiki?curid=49090 |
23,799 | The Drude model treats electrons (or other charge carriers) like pinballs bouncing among the ions that make up the structure of the material. Electrons will be accelerated in the opposite direction to the electric field by the average electric field at their location. With each collision, though, the electron is deflec... | https://en.wikipedia.org/wiki?curid=49090 |
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