document_title: List of forms of government

question_text: a political system that is ruled by a few is called

text: List of forms of government

text: Forms of government by power structure[edit]

text:
Term
Definition

Unitary State
A unitary state is a state governed as a single power in which the central government is ultimately supreme and any administrative divisions (sub-national units) exercise only the powers that the central government chooses to delegate. The majority of states in the world have a unitary system of government. Of the 193 UN member states, 165 are governed as unitary states.

Federation
A federation (also known as a federal state) is a political entity characterized by a union of partially self-governing states or regions under a central (federal) government. In a federation, the self-governing status of the component states, as well as the division of power between them and the central government, is typically constitutionally entrenched and may not be altered by a unilateral decision of either party, the states or the federal political body. Alternatively, federation is a form of government in which sovereign power is formally divided between a central authority and a number of constituent regions so that each region retains some degree of control over its internal affairs.

Confederation
A confederation (also known as a confederacy or league) is a union of sovereign states, united for purposes of common action often in relation to other states. Usually created by a treaty, confederations of states tend to be established for dealing with critical issues, such as defense, foreign relations, internal trade or currency, with the general government being required to provide support for all its members. Confederalism represents a main form of inter-governmentalism, this being defined as ‘any form of interaction between states which takes place on the basis of sovereign independence or government.

text: Forms of government by power source[edit]

text:
Term
Description

Democracy
Democracy, meaning "rule of the people", is a system of government in which the citizens exercise power directly or elect representatives from among themselves to form a governing body, such as a parliament. Democracy is sometimes referred to as "rule of the majority". Democracy is a system of processing conflicts in which outcomes depend on what participants do, but no single force controls what occurs and its outcomes.

Oligarchy
Oligarchy, meaning "rule of the few", is a form of power structure in which power rests with a small number of people. These people might be distinguished by nobility, wealth, family ties, education or corporate, religious or military control. Such states are often controlled by families who typically pass their influence from one generation to the next, but inheritance is not a necessary condition for the application of this term.

Autocracy
Autocracy is a system of government in which supreme power (social and political) is concentrated in the hands of one person, whose decisions are subject to neither external legal restraints nor regularized mechanisms of popular control (except perhaps for the implicit threat of a coup d'état or mass insurrection). Absolute monarchy (such as Saudi Arabia, the United Arab Emirates, Oman, Brunei and Swaziland) and dictatorships (such as Cuba, China, and North Korea) are the main modern day forms of autocracy.

text: Types of democracy[edit]

text: In democracies, large proportions of the population may vote, either to make decisions or to choose representatives to make decisions. Commonly significant in democracies are political parties, which are groups of people with similar ideas about how a country or region should be governed. Different political parties have different ideas about how the government should handle different problems.

text: Note: These categories are not exclusive

text:
Term
Definition

Direct democracy
Variant of democracy; government in which the people represent themselves and vote directly for new laws and public policy.

Representative democracy
Variant of democracy; wherein the people or citizens of a country elect representatives to create and implement public policy in place of active participation by the people.

Liberal democracy
Variant of democracy; a form of government in which representative democracy operates under the principles of liberalism. It is characterised by fair, free, and competitive elections between multiple distinct political parties, a separation of powers into different branches of government, the rule of law in everyday life as part of an open society, and the protection of human rights and civil liberties for all persons. To define the system in practice, liberal democracies often draw upon a constitution, either formally written or uncodified, to delineate the powers of government and enshrine the social contract. After a period of sustained expansion throughout the 20th century, liberal democracy became the predominant political system in the world. A liberal democracy may take various constitutional forms: it may be a republic, such as France, Germany, India, Ireland, Italy, Taiwan, or the United States; or a constitutional monarchy, such as Japan, Spain, or the United Kingdom. It may have a presidential system (Argentina, Brazil, Mexico, or the United States), a semi-presidential system (France, Portugal, or Taiwan), or a parliamentary system (Australia, Canada, Germany, Ireland, India, Italy, New Zealand, or the United Kingdom).

Social democracy
Variant of democracy; social democracy rejects the "either/or" phobiocratic/polarisation interpretation of capitalism versus socialism. It claims that fostering a progressive evolution of capitalism will gradually result in the evolution of capitalist economy into socialist economy. Social democracy argues that all citizens should be legally entitled to certain social rights. These are made up of universal access to public services such as: education, health care, workers' compensation, public transportation, and other services including child care and care for the elderly. Social democracy is connected with the trade union labour movement and supports collective bargaining rights for workers. Contemporary social democracy advocates freedom from discrimination based on differences of: ability/disability, age, ethnicity, sex, gender, language, race, religion, sexual orientation, and social class.

Totalitarian democracy
Variant of democracy; refers to a system of government in which lawfully elected representatives maintain the integrity of a nation state whose citizens, while granted the right to vote, have little or no participation in the decision-making process of the government.

Electocracy
Variant of democracy where citizens are able to vote for their government but cannot participate directly in governmental decision making and where the government does not share any power.

Demarchy
Variant of democracy; government in which the state is governed by randomly selected decision makers who have been selected by sortition (lot) from a broadly inclusive pool of eligible citizens. These groups, sometimes termed "policy juries", "citizens' juries", or "consensus conferences", deliberately make decisions about public policies in much the same way that juries decide criminal cases. Demarchy, in theory, could overcome some of the functional problems of conventional representative democracy, which is widely subject to manipulation by special interests and a division between professional policymakers (politicians and lobbyists) vs. a largely passive, uninvolved and often uninformed electorate. According to Australian philosopher John Burnheim, random selection of policymakers would make it easier for everyday citizens to meaningfully participate, and harder for special interests to corrupt the process.
More generally, random selection of decision makers from a larger group is known as sortition (from the Latin base for lottery). The Athenian democracy made much use of sortition, with nearly all government offices filled by lottery (of full citizens) rather than by election. Candidates were almost always male, Greek, educated citizens holding a minimum of wealth and status.

text: Types of oligarchy[edit]

text: Oligarchicies are societies controlled and organised by a small class of privileged people, with no intervention from the most part of society; this small elite is defined as sharing some common trait.

text: De jure democratic governments with a de facto oligarchy are ruled by a small group of segregated, powerful or influential people who usually share similar interests or family relations. These people may spread power and elect candidates equally or not equally. An oligarchy is different from a true democracy because very few people are given the chance to change things. An oligarchy does not have to be hereditary or monarchic. An oligarchy does not have one clear ruler but several rulers.

text: Some historical examples of oligarchy are the Roman Republic, in which only males of the nobility could run for office and only wealthy males could vote, and the Athenian democracy, which used sortition to elect candidates, almost always male, Greek, educated citizens holding a minimum of land, wealth and status. Some critics of capitalism and/or representative democracy think of the United States as an oligarchy.

text:
Term
Definition

Aristocracy
Rule by the nobility; a system of governance where political power is in the hands of a small class of privileged individuals who claim a higher birth than the rest of society.

Plutocracy
Rule by the wealthy; a system wherein governance is indebted to, dependent upon or heavily influenced by the desires of the rich. Plutocratic influence can alter any form of government. For instance, in a republic, if a significant number of elected representative positions are dependent upon financial support from wealthy sources, it is a plutocratic republic.

Kraterocracy
Rule by the strong; a system of governance where those who are strong enough to seize power through physical force, social maneuvering or political cunning.

Stratocracy
Rule by military service; a system of governance composed of military government in which the state and the military are traditionally or constitutionally the same entity. Citizens with mandatory or voluntary active military service or who have been honorably discharged have the right to govern (not to be confused with "military junta" or "military dictatorship"). The Spartan city-state is a historical example; its social system and constitution were completely focused on military training and excellence. Stratocratic ideology often attaches to the honor-oriented timocracy.

Timocracy
Rule by the honourable; a system of governance ruled by honorable citizens and property owners. Socrates defines a timocracy as a government ruled by people who love honour and are selected according to the degree of honour they hold in society. This form of timocracy is very similar to meritocracy, in the sense that individuals of outstanding character or faculty are placed in the seat of power.

Meritocracy
Rule by the meritorious; a system of governance where groups are selected on the basis of people's ability, knowledge in a given area, and contributions to society.

Technocracy
Rule by the educated or technical experts; a system of governance where people who are skilled or proficient govern in their respective areas of expertise in technology would be in control of all decision making. Doctors, engineers, scientists, professionals and technologists who have knowledge, expertise, or skills would compose the governing body instead of politicians, businessmen and economists.[1] In a technocracy, decision makers would be selected based upon how knowledgeable and skillful they are in their field.

Geniocracy
Rule by the intelligent; a system of governance where creativity, innovation, intelligence and wisdom are required for those who wish to govern. Comparable to noocracy.

Noocracy
Rule by the wise; a system of governance in which decision making is in the hands of philosophers. (advocated by Plato)

Theocracy
Rule by a religious elite; a system of governance composed of religious institutions in which the state and the church are traditionally or constitutionally the same entity. The Vatican's (see Pope), Iran's (see Supreme Leader), Tibetan government's (see Dalai Lama), Caliphates and other Islamic states are historically considered theocracies.

Kritarchy
Rule by various judges, the kritarchs; a system of governance composed of law enforcement institutions in which the state and the legal systems are traditionally or constitutionally the same entity. The kritarchs, magistrates and other adjudicators have the legal power to legislate and administer the enforcement of government laws in addition to the interposition of laws and the resolution of disputes. (Not to be confused with "judiciary" or "judicial system".) Somalia, ruled by judges with the tradition of xeer,[2] as well as the Islamic Courts Union, is a historical example.[3]

Particracy
Rule by a dominant political party (or parties).

Ergatocracy
Rule by the proletariat, the workers, or the working class. Examples of ergatocracy include communist revolutionaries and rebels which control most of society and create an alternative economy for people and workers. See Dictatorship of the proletariat.

Netocracy
Rule by social connections; a term invented by the editorial board of the American technology magazine Wired in the early 1990s. A portmanteau of Internet and aristocracy, netocracy refers to a perceived global upper-class that bases its power on a technological advantage and networking skills, in comparison to what is portrayed as a bourgeoisie of a gradually diminishing importance. The netocracy concept has been compared with Richard Florida's concept of the creative class. Bard and Söderqvist have also defined an under-class in opposition to the netocracy, which they refer to as the consumtariat.

text: Types of autocracy[edit]

text: Autocracies are ruled by a single entity with absolute power, whose decisions are subject to neither external legal restraints nor regular mechanisms of popular control (except perhaps for implicit threat). That entity may be an individual, as in a dictatorship or it may be a group, as in a one-party state. The word despotism means to "rule in the fashion of despots" and is often used to describe autocracy.

text: Historical examples of autocracy include the Roman Empire, Soviet Union and Nazi Germany.

text:
Term
Definition

Civilian Dictatorship
A dictatorship where power resides in the hands of one single person or polity. That person may be, for example, an absolute monarch or a dictator, but can also be an elected president. The Roman Republic made dictators to lead during times of war; but the Roman dictators only held power for a small time. In modern times, an autocrat's rule is one that not stopped by any rules of law, constitutions, or other social and political institutions. After World War II, many governments in Latin America, Asia, and Africa were ruled by autocratic governments. Examples of dictators include: Joseph Stalin, Adolf Hitler, Mao Zedong, Idi Amin, Muammar Gaddafi, and Gamal Abdul Nasser.

Military Dictatorship
A dictatorship primarily enforced by the military. Military dictators are different from civilian dictators for a number of reasons: their motivations for seizing power, the institutions through which they organize their rule, and the ways in which they leave power. Often viewing itself as saving the nation from the corrupt or myopic civilian politicians, a military dictatorship justifies its position as “neutral” arbiters on the basis of their membership within the armed forces. For example, many juntas adopt titles, such as “National Redemption Council", “Committee of National Restoration", or “National Liberation Committee". Military leaders often rule as a junta, selecting one of them as the head.

text: Pejorative attributes[edit]

text: Regardless of the form of government, the actual governance may be influenced by sectors with political power which are not part of the formal government. These are terms that highlight certain actions of the governors, such as corruption, demagoguery, or fear mongering that may disrupt the intended way of working of the government if they are widespread enough.

text:
Term
Definition

Bankocracy
Rule by banks;[4] a system of governance with excessive power or influence of banks and other financial authorities on public policy-making. It can also refer to a form of government where financial institutions rule society.

Corporatocracy
Rule by corporations; a system of governance where an economic and political system is controlled by corporations or corporate interests.[5] Its use is generally pejorative. Examples include company rule in India and business voters for the City of London Corporation.

Nepotocracy
Rule by nephews; favouritism granted to relatives regardless of merit; a system of governance in which importance is given to the relatives of those already in power, like a nephew (where the word comes from). In such governments even if the relatives aren't qualified they are given positions of authority just because they know someone who already has authority. Pope Alexander VI (Borgia) was accused of this.

Kakistocracy
Rule by the stupid; a system of governance where the worst or least-qualified citizens govern or dictate policies. Due to human nature being inherently flawed, it has been suggested that every government which has ever existed has been a prime example of kakistocracy. See Idiocracy.

Kleptocracy
Rule by thieves; a system of governance where its officials and the ruling class in general pursue personal wealth and political power at the expense of the wider population. In strict terms kleptocracy is not a form of government but a characteristic of a government engaged in such behavior. Examples include Mexico as being considered a "narcokleptocracy", (narco-state) since its democratic government is perceived to be corrupted by those who profit from trade in illegal drugs smuggled into the United States and Vladimir Putin's style of government in the Russian Federation often called mafia state.

Ochlocracy
Rule by the crowd; a system of governance where mob rule is government by mob or a mass of people, or the intimidation of legitimate authorities. As a pejorative for majoritarianism, it is akin to the Latin phrase mobile vulgus meaning "the fickle crowd", from which the English term "mob" was originally derived in the 1680s. Ochlocratic governments are often a democracy spoiled by demagoguery, "tyranny of the majority" and the rule of passion over reason; such governments can be as oppressive as autocratic tyrants. Ochlocracy is synonymous in meaning and usage to the modern, informal term "mobocracy".

text: Other attributes[edit]

text:
Term
Definition

Anocracy
A regime type where power is not vested in public institutions (as in a normal democracy) but spread amongst elite groups who are constantly competing with each other for power. Examples of anocracies in Africa include the warlords of Somalia and the shared governments in Kenya and Zimbabwe. Anocracies are situated midway between an autocracy and a democracy.[6]
The Polity IV dataset[clarification needed] recognised anocracy as a category. In that dataset, anocracies are exactly in the middle between autocracies and democracies.
Often the word is defined more broadly. For example, a 2010 International Alert publication defined anocracies as "countries that are neither autocratic nor democratic, most of which are making the risky transition between autocracy and democracy".[7] Alert noted that the number of anocracies had increased substantially since the end of the Cold War. Anocracy is not surprisingly the least resilient political system to short-term shocks: it creates the promise but not yet the actuality of an inclusive and effective political economy, and threatens members of the established elite; and is therefore very vulnerable to disruption and armed violence.

Adhocracy
Rule by a government based on relatively disorganised principles and institutions as compared to a bureaucracy, its exact opposite.

Bureaucracy
Rule by a system of governance with many bureaus, administrators, and petty officials

Cybersynacy
Ruled by a data fed group of secluded individuals that regulates aspects of public and private life using data feeds and technology having no interactivity with the citizens but using "facts only" to decide direction.

Nomocracy
Rule by a government under the sovereignty of rational laws and civic right as opposed to one under theocratic systems of government. In a nomocracy, ultimate and final authority (sovereignty) exists in the law.

Banana republic
A politically unstable and kleptocratic government that economically depends upon the exports of a limited resource (fruits, minerals), and usually features a society composed of stratified social classes, such as a great, impoverished ergatocracy and a ruling plutocracy, composed of the aristocracy of business, politics, and the military.[8] In political science, the term banana republic denotes a country dependent upon limited primary-sector productions, which is ruled by a plutocracy who exploit the national economy by means of a politico-economic oligarchy.[9] In American literature, the term banana republic originally denoted the fictional Republic of Anchuria, a servile dictatorship that abetted, or supported for kickbacks, the exploitation of large-scale plantation agriculture, especially banana cultivation.[9] In U.S. politics, the term banana republic is a pejorative political descriptor coined by the American writer O. Henry in Cabbages and Kings (1904), a book of thematically related short stories derived from his 1896–1897 residence in Honduras, where he was hiding from U.S. law for bank embezzlement.[10]

Band society
Rule by a government based on small (usually family) unit with a semi-informal hierarchy, with strongest (either physical strength or strength of character) as leader. Very much like a pack seen in other animals, such as wolves.

text: Forms of government by ideology[edit]

text: By socio-political attributes[edit]

text:
Term
Definition

Anarchy
A society without a publicly enforced government or political authority.[11][12] Sometimes said to be non-governance; it is a structure which strives for non-hierarchical, voluntary associations among agents. Anarchy is a situation where there is no state. When used in this sense, anarchy may[13] or may not[14] be intended to imply political disorder or lawlessness within a society.
This can be a natural, temporary result of civil war in a country, when an established state has been destroyed and the region is in a transitional period without definitive leadership.[15] Alternatively, it has been presented as a viable long term choice by individuals who oppose the state and other forms of coercive hierarchies. These individuals typically think people should organize in non-hierarchical, voluntary associations where people voluntarily help each other.[16] There are a variety of forms of anarchy that attempt to avoid the use of coercion, violence, force and authority, while still producing a productive and desirable society.[17][18]
This is not the same as Anarchism.

Monarchy
A monarchy is a form of government in which a group, generally a family representing a dynasty, embodies the country's national identity and its head, the monarch, exercises the role of sovereignty. The actual power of the monarch may vary from purely symbolic (crowned republic), to partial and restricted (constitutional monarchy), to completely autocratic (absolute monarchy). Traditionally the monarch's post is inherited and lasts until death or abdication. In contrast, elective monarchies require the monarch to be elected. Both types have further variations as there are widely divergent structures and traditions defining monarchy. For example, in some[which?]elected monarchies only pedigrees are taken into account for eligibility of the next ruler, whereas many hereditary monarchies impose requirements regarding the religion, age, gender, mental capacity, etc. Occasionally this might create a situation of rival claimants whose legitimacy is subject to effective election. There have been cases where the term of a monarch's reign is either fixed in years or continues until certain goals are achieved: an invasion being repulsed, for instance.

Republic
A republic (Latin: res publica) is a form of government in which the country is considered a "public matter", not the private concern or property of the rulers. The primary positions of power within a republic are not inherited, but are attained through elections expressing the consent of the governed. Such leadership positions are therefore expected to fairly represent the citizen body. It is a form of government under which the head of state is not a monarch. In American English, the definition of a republic can also refer specifically to a government in which elected individuals represent the citizen body, known elsewhere as a representative democracy (a democratic republic) and exercise power according to the rule of law (a constitutional republic).

text: Types of monarchy[edit]

text: Countries with monarchy attributes are those where a family or group of families (rarely another type of group), called the royalty, represents national identity, with power traditionally assigned to one of its individuals, called the monarch, who mostly rule kingdoms. The actual role of the monarch and other members of royalty varies from purely symbolical (crowned republic) to partial and restricted (constitutional monarchy) to completely despotic (absolute monarchy). Traditionally and in most cases, the post of the monarch is inherited, but there are also elective monarchies where the monarch is elected.

text:
Term
Definition

Absolute monarchy
A traditional and historical system where the monarch exercises ultimate governing authority as head of state and head of government. Many nations of Europe during the Middle Ages were absolute monarchies. Modern examples include mainly Islamic countries such as Saudi Arabia, UAE, Oman, Brunei and one African country Swaziland.

Constitutional monarchy
Also called parliamentary monarchy, the monarch's powers are limited by law or by a formal constitution,[19][20] usually assigning them to those of the head of state. Many modern developed countries, including the United Kingdom, Norway, Netherlands, Australia, Canada and Japan, are constitutional monarchy systems.

Crowned republic
A form of government where the monarch (and family) is an official ceremonial entity with no political power. The royal family and the monarch are intended to represent the country and may perform speeches or attend an important ceremonial events as a symbolical guide to the people, but hold no actual power in decision-making, appointments, et cetera.

text: Types of republic[edit]

text: Rule by a form of government in which the people, or some significant portion of them, have supreme control over the government and where offices of state are elected or chosen by elected people.[21][22] A common simplified definition of a republic is a government where the head of state is not a monarch.[23][24] Montesquieu included both democracies, where all the people have a share in rule, and aristocracies or oligarchies, where only some of the people rule, as republican forms of government.[25]

text:
Term
Definition

Constitutional Republic
Republics where there is rule by a government whose powers are limited by law or a formal constitution, and chosen by a vote amongst at least some sections of the populace (Ancient Sparta was in its own terms a republic, though most inhabitants were disenfranchised). Republics that exclude sections of the populace from participation will typically claim to represent all citizens (by defining people without the vote as "non-citizens"). Examples include the United States, South Africa, India, etc.

Democratic republic
Republics where the running of the country is considered a "public matter" (Latin: res publica), not a private concern or property of rulers, and where offices of states are subsequently, directly or indirectly, elected or appointed – rather than inherited – where all eligible citizens have an equal say in the local and national decisions that affect their lives.

Parliamentary republic
Republics, like Germany, India or Singapore, with an elected head of state, but where the head of state and head of government are kept separate with the head of government retaining most executive powers, or a head of state akin to a head of government, elected by a parliament.

Presidential Republic
Republics with an elected head of state, where the head of state is also the head of the government. Examples include United States, Mexico, Brazil, and Indonesia.

Federal republic
Republics that are a federal union of states or provinces Examples include United States, Argentina, Austria, Brazil, Germany, India, Mexico, Russia, and Switzerland.

People's republic
Republics that include countries like China and Vietnam that are de jure governed for and by the people, but with no direct elections. The term People's Republic is used to differentiate themselves from the earlier republic of their countries before the people's revolution, like the Republic of China.

Islamic Republic
Republics governed in accordance with Islamic law. Examples include Afghanistan, Pakistan, and Iran.

text: By socio-economic attributes[edit]

text: Historically, most political systems originated as socioeconomic ideologies. Experience with those movements in power and the strong ties they may have to particular forms of government can cause them to be considered as forms of government in themselves.

text:
Term
Definition

Tribalism
A system based on a small complex society of varying degrees of centralisation that is led by an individual known as a chief.

Despotism
A system in which the land and resources of a nation are controlled by one individual, usually a king or emperor, who holds absolute political power. Examples include the pharaohs of Ancient Egypt and the Roman emperors.

Feudalism
A system of land ownership and duties common to medieval Europe. Under feudalism, all the land in a kingdom was the king's. However, the king would give some of the land to the lords or nobles who fought for him. These presents of land were called manors. Then the nobles gave some of their land to vassals. The vassals then had to do duties for the nobles. The lands of vassals were called fiefs.
A similar system is the Iqta, used by medieval Islamic societies of the middle east and north africa. This functioned much like the feudal system but generally had titles that weren't granted to a family dynasty but to individuals at the behest of the sultan and generally only required a tax from the lower classes, instead of military service and /or manual labour like in the feudal system.

Colonialism
A system in which a native group (or their lands and resources) is subjugated by an external political power for their own economic and/or political benefit.

Capitalism
A system in which the means of production (machines, tools, factories, etc.) are owned by private individuals, workers then negotiate with those individuals to use those means of production in exchange for a portion of what they produce, usually in the form of capital (money). The owners of the means of production are entitled to whatever portion of the products of the workers' labor that is agreed upon by the two parties.
The capitalist system is usually accompanied by a Welfare state which plays a key role in the protection and promotion of the economic and social well-being of its citizens. It is based on the principles of equality of opportunity, equitable distribution of wealth, and public responsibility for those unable to avail themselves of the minimal provisions for a good life.

Minarchism
A variant of capitalism which advocates for the State to exist solely to provide a very small number of services. A popular model of the State proposed by minarchists is known as the night-watchman state, in which the only governmental functions are to protect citizens from aggression, theft, breach of contract, and fraud as defined by property laws, limiting it to three institutions: the military, the police, and courts.

Distributism
A variant of capitalism which views widespread property ownership as fundamental right;[26] the means of production are spread as widely as possible rather than being centralized under the control of the state (as in state socialism), or a few individuals/corporations (as in what proponents of distributism call "crony capitalism")[27] Distributism fundamentally opposes socialism and capitalism,[28][29] which distributists view as equally flawed and exploitative. In contrast, distributism seeks to subordinate economic activity to human life as a whole, to our spiritual life, our intellectual life, our family life".[30]

Socialism
A system in which workers, democratically and socially own the means of production.[31] The economic framework may be decentralized and self-managed in autonomous economic units, as in libertarian systems, or centrally planned, as in authoritarian systems.[32] Public services such as healthcare and education would be commonly, collectively, and/or state owned.

Anarchism
A socialist system that advocates self-governed societies based on voluntary institutions. These are often described as stateless societies, although several authors have defined them more specifically as institutions based on non-hierarchical or free associations. Anarchism holds the state to be undesirable, unnecessary, and/or harmful.

Communism
A socialist system in which the means of production are commonly owned (either by the people directly, through the commune, or by a communist state or society), and production is undertaken for use, rather than for profit.[33][34] Communist society is thus, in theory, stateless, classless, moneyless, and democratic — usually regarded as the "final form" of a socialist or anarchist society.

Totalitarianism
A system in which the land and resources of a nation are controlled by a centralised authoritarian state that holds absolute political power, usually under a dictatorship or single political party. Examples include the Soviet Union and Nazi Germany.

text: By geo-cultural attributes[edit]

text: Governments can also be categorised based on their size and scope of influence:

text:
Term
Definition

Commune
From the Medieval Latin communia. An intentional community of people living together, sharing common interests, often having common values and beliefs, as well as shared property, possessions, resources, and, in some communes, work, income or assets.

City-State
A sovereign state, also described as a type of small independent country, that usually consists of a single city and its dependent territories. Historically, this included cities such as Rome, Athens, Carthage, and the Italian city-states during the Renaissance. Today only a handful of sovereign city-states exist, with some disagreement as to which are city-states. A great deal of consensus exists that the term properly applies currently to Singapore, Monaco, and Vatican City. City states are also sometimes called micro-states which however also includes other configurations of very small countries.

National Government
The government of a nation-state and is a characteristic of a unitary state. This is the same thing as a federal government which may have distinct powers at various levels authorized or delegated to it by its member states, though the adjective 'central' is sometimes used to describe it. The structure of central governments varies. Many countries have created autonomous regions by delegating powers from the central government to governments at a subnational level, such as a regional, state or local level. Based on a broad definition of a basic political system, there are two or more levels of government that exist within an established territory and govern through common institutions with overlapping or shared powers as prescribed by a constitution or other law.

Intergovernmental Organisations
Also known as international governmental organizations (IGOs): the type of organization most closely associated with the term 'international organization', these are organizations that are made up primarily of sovereign states (referred to as member states). Notable examples include the United Nations (UN), Organization for Security and Co-operation in Europe (OSCE), Council of Europe (COE), International Labour Organization (ILO) and International Police Organization (INTERPOL). The UN has used the term "intergovernmental organization" instead of "international organization" for clarity.

World Government
The notion of a common political authority for all of humanity, yielding a global government and a single state that exercises authority over the entire Earth. Such a government could come into existence either through violent and compulsory world domination or through peaceful and voluntary supranational union.

text: Forms of government by other attributes[edit]

text: By significant constitutional attributes[edit]

text: Certain major characteristics are defining of certain types; others are historically associated with certain types of government.

text:
Rule according to higher law (unwritten ethical principles) vs. written constitutionalism
Separation of church and state or free church vs. state religion
Civilian control of the military vs. stratocracy
Totalitarianism or authoritarianism vs. libertarianism
Majority rule or parliamentary sovereignty vs. constitution or bill of rights with separation of powers and supermajority rules to prevent tyranny of the majority and protect minority rights
Androcracy (patriarchy) or gynarchy (matriarchy) vs. gender quotas, gender equality provision, or silence on the matter

tag: ul

text: By approach to regional autonomy[edit]

text: This list focuses on differing approaches that political systems take to the distribution of sovereignty, and the autonomy of regions within the state.

text:
Sovereignty located exclusively at the centre of political jurisdiction.

Empire
Unitary state

Sovereignty located at the centre and in peripheral areas.

Hegemony
Federation and federal republic
Confederation
Federal monarchy

Diverging degrees of sovereignty.

Alliance
Asymmetrical federalism
Federacy
Associated state
Corpus separatum
Colony
Crown colony
Chartered company
Dependent territory
Occupied territory
Occupied zone
Mandate
Exclusive mandate
Military Frontier
Neutral zone
Colonial dependency
Protectorate
Vassal state
Satellite state
Puppet state
Thalassocracy
Unrecognized state

States with limited recognition
Separatist movement
Government in exile
Micronation

Provisional government
Territorial disputes
Non-self-governing territories
League of Nations
League
Commonwealth
Decentralisation and devolution (powers redistributed from central to regional or local governments)

text: Theoretical and speculative attributes[edit]

text: These currently have no citable real-world examples outside of fiction.

text:
Term
Definition

Corporate republic
Theoretical form of government occasionally hypothesised in works of science fiction, though some historical nations such as medieval Florence might be said to have been governed as corporate republics. The colonial megacorporations such as the Dutch East India Company should possibly be considered corporate states, being semi-sovereign with the power to wage war and establish colonies.
While retaining some semblance of republican government, a corporate republic would be run primarily like a business, involving a board of directors and executives. Utilities, including hospitals, schools, the military, and the police force, would be privatised. The social welfare function carried out by the state is instead carried out by corporations in the form of benefits to employees. Although corporate republics do not exist officially in the modern world, they are often used in works of fiction or political commentary as a warning of the perceived dangers of unbridled capitalism. In such works, they usually arise when a single, vastly powerful corporation deposes a weak government, over time or in a coup d'état.
Some political scientists have also considered state socialist nations to be forms of corporate republics, with the state assuming full control of all economic and political life and establishing a monopoly on everything within national boundaries – effectively making the state itself amount to a giant corporation.

Magocracy
Rule by a government with the highest and main authority being either a magician, sage, sorcerer, wizard or witch. This is often similar to a theocratic structured regime and is largely portrayed in fiction and fantasy genre categories.

Uniocracy
Ruled by a singularity of all human minds connected via some form of technical or non-technical telepathy acting as a form of super computer to make decisions based on shared patterned experiences to deliver fair and accurate decisions to problems as they arrive. Also known as the "Hive Mind" principle, it differs from voting in that each person would make a decision while in the "hive" the synapses of all minds work together following a longer path of memories to make "one" decision.


document_title: Brushed DC electric motor

question_text: what factors determine the amount of torque on the armature of a rotating dc electric motor

root

text: Brushed DC electric motor

text: Simple two-pole DC motor[edit]

text: The following graphics illustrate a simple, two-pole, brushed, DC motor.

tag: p

text: When a current passes through the coil wound around a soft iron core, the side of the positive pole is acted upon by an upwards force, while the other side is acted upon by a downward force. According to Fleming's left hand rule, the forces cause a turning effect on the coil, making it rotate. To make the motor rotate in a constant direction, "direct current" commutators make the current reverse in direction every half a cycle (in a two-pole motor) thus causing the motor to continue to rotate in the same direction.

text: A problem with the motor shown above is that when the plane of the coil is parallel to the magnetic field—i.e. when the rotor poles are 90 degrees from the stator poles—the torque is zero. In the pictures above, this occurs when the core of the coil is horizontal—the position it is just about to reach in the last picture on the right. The motor would not be able to start in this position. However, once it was started, it would continue to rotate through this position by momentum.

text: There is a second problem with this simple pole design. At the zero-torque position, both commutator brushes are touching (bridging) both commutator plates, resulting in a short-circuit. The power leads are shorted together through the commutator plates, and the coil is also short-circuited through both brushes (the coil is shorted twice, once through each brush independently). Note that this problem is independent of the non-starting problem above; even if there were a high current in the coil at this position, there would still be zero torque. The problem here is that this short uselessly consumes power without producing any motion (nor even any coil current.) In a low-current battery-powered demonstration this short-circuiting is generally not considered harmful. However, if a two-pole motor were designed to do actual work with several hundred watts of power output, this shorting could result in severe commutator overheating, brush damage, and potential welding of the brushes—if they were metallic—to the commutator. Carbon brushes, which are often used, would not weld. In any case, a short like this is very wasteful, drains batteries rapidly and, at a minimum, requires power supply components to be designed to much higher standards than would be needed just to run the motor without the shorting.

text: One simple solution is to put a gap between the commutator plates which is wider than the ends of the brushes.  This increases the zero-torque range of angular positions but eliminates the shorting problem; if the motor is started spinning by an outside force it will continue spinning.  With this modification, it can also be effectively turned off simply by stalling (stopping) it in a position in the zero-torque (i.e. commutator non-contacting) angle range.  This design is sometimes seen in homebuilt hobby motors, e.g. for science fairs and such designs can be found in some published science project books.  A clear downside of this simple solution is that the motor now coasts through a substantial arc of rotation twice per revolution and the torque is pulsed.  This may work for electric fans or to keep a flywheel spinning but there are many applications, even where starting and stopping are not necessary, for which it is completely inadequate, such as driving the capstan of a tape transport, or any instance where to speed up and slow down often and quickly is a requirement. Another disadvantage is that, since the coils have a measure of self inductance, current flowing in them cannot suddenly stop. The current attempts to jump the opening gap between the commutator segment and the brush, causing arcing.

text: Even for fans and flywheels, the clear weaknesses remaining in this design—especially that it is not self-starting from all positions—make it impractical for working use, especially considering the better alternatives that exist.  Unlike the demonstration motor above, DC motors are commonly designed with more than two poles, are able to start from any position, and do not have any position where current can flow without producing electromotive power by passing through some coil.  Many common small brushed DC motors used in toys and small consumer appliances, the simplest mass-produced DC motors to be found, have three-pole armatures. The brushes can now bridge two adjacent commutator segments without causing a short circuit. These three-pole armatures also have the advantage that current from the brushes either flows through two coils in series or through just one coil. Starting with the current in an individual coil at half its nominal value (as a result of flowing through two coils in series), it rises to its nominal value and then falls to half this value. The sequence then continues with current in the reverse direction. This results in a closer step-wise approximation to the ideal sinusoidal coil current, producing a more even torque than the two-pole motor where the current in each coil is closer to a square wave. Since current changes are half those of a comparable two-pole motor, arcing at the brushes is consequently less.

text: If the shaft of a DC motor is turned by an external force, the motor will act like a generator and produce an Electromotive force (EMF).  During normal operation, the spinning of the motor produces a voltage, known as the counter-EMF (CEMF) or back EMF, because it opposes the applied voltage on the motor.  The back EMF is the reason that the motor when free-running does not appear to have the same low electrical resistance as the wire contained in its winding.  This is the same EMF that is produced when the motor is used as a generator (for example when an electrical load, such as a light bulb, is placed across the terminals of the motor and the motor shaft is driven with an external torque).  Therefore, the total voltage drop across a motor consists of the CEMF voltage drop, and the parasitic voltage drop resulting from the internal resistance of the armature's windings.  The current through a motor is given by the following equation:

text: The mechanical power produced by the motor is given by:

text: As an unloaded DC motor spins, it generates a backwards-flowing electromotive force that resists the current being applied to the motor. The current through the motor drops as the rotational speed increases, and a free-spinning motor has very little current. It is only when a load is applied to the motor that slows the rotor that the current draw through the motor increases.

text: The commutating plane[edit]

text: In a dynamo, a plane through the centers of the contact areas where a pair of brushes touch the commutator and parallel to the axis of rotation of the armature is referred to as the commutating plane. In this diagram the commutating plane is shown for just one of the brushes, assuming the other brush made contact on the other side of the commutator with radial symmetry, 180 degrees from the brush shown.

tag: table

text: Compensation for stator field distortion[edit]

text: In a real dynamo, the field is never perfectly uniform. Instead, as the rotor spins it induces field effects which drag and distort the magnetic lines of the outer non-rotating stator.

text:
Exaggerated example of how the field is distorted by the rotor.

 Iron filings show the distorted field across the rotor.

text: The faster the rotor spins, the further the degree of field distortion. Because the dynamo operates most efficiently with the rotor field at right angles to the stator field, it is necessary to either retard or advance the brush position to put the rotor's field into the correct position to be at a right angle to the distorted field.

text:
Centered position of the commutating plane if there were no field distortion effects.

 Actual position of the commutating plane to compensate for field distortion.

text: These field effects are reversed when the direction of spin is reversed. It is therefore difficult to build an efficient reversible commutated dynamo, since for highest field strength it is necessary to move the brushes to the opposite side of the normal neutral plane.

text: The effect can be considered to be somewhat similar to timing advance in an internal combustion engine. Generally a dynamo that has been designed to run at a certain fixed speed will have its brushes permanently fixed to align the field for highest efficiency at that speed.[1]

text: Motor design variations[edit]

text: DC motors[edit]

text: Brushed DC motors are constructed with wound rotors and either wound or permanent-magnet stators.

text: Wound stators[edit]

text: A, ShuntB, SeriesC, Compoundf, Field coil

text: The field coils have traditionally existed in four basic formats: separately excited (sepex), series-wound, shunt-wound, and a combination of the latter two; compound-wound.

text: In a series wound motor, the field coils are connected electrically in series with the armature coils (via the brushes). In a shunt wound motor, the field coils are connected in parallel, or "shunted" to the armature coils. In a separately excited (sepex) motor the field coils are supplied from an independent source, such as a motor-generator and the field current is unaffected by changes in the armature current. The sepex system was sometimes used in DC traction motors to facilitate control of wheelslip.

text: Permanent-magnet motors[edit]

text: Permanent-magnet types have some performance advantages over direct-current, excited, synchronous types, and have become predominant in fractional horsepower applications. They are smaller, lighter, more efficient and reliable than other singly-fed electric machines.[2]

text: Originally all large industrial DC motors used wound field or rotor magnets. Permanent magnets have traditionally only been useful on small motors because it was difficult to find a material capable of retaining a high-strength field. Only recently have advances in materials technology allowed the creation of high-intensity permanent magnets, such as neodymium magnets, allowing the development of compact, high-power motors without the extra real-estate of field coils and excitation means. But as these high performance permanent magnets become more applied in electric motor or generator systems, other problems are realized (see Permanent magnet synchronous generator).

text: Axial field motors[edit]

text: Traditionally, the field has been applied radially—in and away from the rotation axis of the motor. However some designs have the field flowing along the axis of the motor, with the rotor cutting the field lines as it rotates. This allows for much stronger magnetic fields, particularly if halbach arrays are employed. This, in turn, gives power to the motor at lower speeds. However, the focused flux density cannot rise about the limited residual flux density of the permanent magnet despite high coercivity and like all electric machines, the flux density of magnetic core saturation is the design constraint.

text: Speed control[edit]

text: Generally, the rotational speed of a DC motor is proportional to the EMF in its coil (= the voltage applied to it minus voltage lost on its resistance), and the torque is proportional to the current. Speed control can be achieved by variable battery tappings, variable supply voltage, resistors or electronic controls. A simulation example can be found here[3] and [4]. The direction of a wound field DC motor can be changed by reversing either the field or armature connections but not both. This is commonly done with a special set of contactors (direction contactors). The effective voltage can be varied by inserting a series resistor or by an electronically controlled switching device made of thyristors, transistors, or, formerly, mercury arc rectifiers.[5]

text: Series-parallel[edit]

text: Series-parallel control was the standard method of controlling railway traction motors before the advent of power electronics. An electric locomotive or train would typically have four motors which could be grouped in three different ways:

text:
All four in series (each motor receives one quarter of the line voltage)
Two parallel groups of two in series (each motor receives half the line voltage)
All four in parallel (each motor receives the full line voltage)

text: This provided three running speeds with minimal resistance losses. For starting and acceleration, additional control was provided by resistances. This system has been superseded by electronic control systems.

text: Field weakening[edit]

text: The speed of a DC motor can be increased by field weakening. Reducing the field strength is done by inserting resistance in series with a shunt field, or inserting resistances around a series-connected field winding, to reduce current in the field winding.  When the field is weakened, the back-emf reduces, so a larger current flows through the armature winding and this increases the speed. Field weakening is not used on its own but in combination with other methods, such as series-parallel control.

text: Chopper[edit]

text: In a circuit known as a chopper, the average voltage applied to the motor is varied by switching the supply voltage very rapidly.  As the "on" to "off" ratio is varied to alter the average applied voltage, the speed of the motor varies. The percentage "on" time multiplied by the supply voltage gives the average voltage applied to the motor. Therefore, with a 100 V supply and a 25% "on" time, the average voltage at the motor will be 25 V. During the "off" time, the armature's inductance causes the current to continue through a diode called a "flyback diode", in parallel with the motor. At this point in the cycle, the supply current will be zero, and therefore the average motor current will always be higher than the supply current unless the percentage "on" time is 100%. At 100% "on" time, the supply and motor current are equal. The rapid switching wastes less energy than series resistors. This method is also called pulse-width modulation (PWM) and is often controlled by a microprocessor. An output filter is sometimes installed to smooth the average voltage applied to the motor and reduce motor noise.

text: Since the series-wound DC motor develops its highest torque at low speed, it is often used in traction applications such as electric locomotives, and trams. Another application is starter motors for petrol and small diesel engines.  Series motors must never be used in applications where the drive can fail (such as belt drives).  As the motor accelerates, the armature (and hence field) current reduces.  The reduction in field causes the motor to speed up until it destroys itself. This can also be a problem with railway motors in the event of a loss of adhesion since, unless quickly brought under control, the motors can reach speeds far higher than they would do under normal circumstances. This can not only cause problems for the motors themselves and the gears, but due to the differential speed between the rails and the wheels it can also cause serious damage to the rails and wheel treads as they heat and cool rapidly. Field weakening is used in some electronic controls to increase the top speed of an electric vehicle. The simplest form uses a contactor and field-weakening resistor; the electronic control monitors the motor current and switches the field weakening resistor into circuit when the motor current reduces below a preset value (this will be when the motor is at its full design speed). Once the resistor is in circuit, the motor will increase speed above its normal speed at its rated voltage. When motor current increases, the control will disconnect the resistor and low speed torque is made available.

text: Ward Leonard[edit]

text: A Ward Leonard control is usually used for controlling a shunt or compound wound DC motor, and developed as a method of providing a speed-controlled motor from an AC supply, though it is not without its advantages in DC schemes.  The AC supply is used to drive an AC motor, usually an induction motor that drives a DC generator or dynamo.  The DC output from the armature is directly connected to the armature of the DC motor (sometimes but not always of identical construction).  The shunt field windings of both DC machines are independently excited through variable resistors.  Extremely good speed control from standstill to full speed, and consistent torque, can be obtained by varying the generator and/or motor field current.  This method of control was the de facto method from its development until it was superseded by solid state thyristor systems.  It found service in almost any environment where good speed control was required, from passenger lifts through to large mine pit head winding gear and even industrial process machinery and electric cranes.  Its principal disadvantage was that three machines were required to implement a scheme (five in very large installations, as the DC machines were often duplicated and controlled by a tandem variable resistor).  In many applications, the motor-generator set was often left permanently running, to avoid the delays that would otherwise be caused by starting it up as required.  Although electronic (thyristor) controllers have replaced most small to medium Ward-Leonard systems, some very large ones (thousands of horsepower) remain in service.  The field currents are much lower than the armature currents, allowing a moderate sized thyristor unit to control a much larger motor than it could control directly.  For example, in one installation, a 300 amp thyristor unit controls the field of the generator.  The generator output current is in excess of 15,000 amperes, which would be prohibitively expensive (and inefficient) to control directly with thyristors.

text: Torque and speed of a DC motor[edit]

text: A DC motor's speed and torque characteristics vary according to three different magnetization sources, separately excited field, self-excited field or permanent-field, which are used selectively to control the motor over the mechanical load's range. Self-excited field motors can be series, shunt, or compound wound connected to the armature.

text: Basic properties[edit]

text: Define

text:
Eb, induced or counter EMF (V)
Ia, armature current (A)
kb, counter EMF equation constant
kn, speed equation constant
kT, torque equation constant
n, armature frequency (rpm)
Rm, motor resistance (Ω)
T, motor torque (Nm)
Vm, motor input voltage (V)
Φ, machine's total flux (Wb)

text: Counter EMF equation[edit]

text: The DC motor's counter emf is proportional to the product of the machine's total flux strength and armature speed:

text: Voltage balance equation[edit]

text: The DC motor's input voltage must overcome the counter emf as well as the voltage drop created by the armature current across the motor resistance, that is, the combined resistance across the brushes, armature winding and series field winding, if any:

text: Torque equation[edit]

text: The DC motor's torque is proportional to the product of the armature current and the machine's total flux strength:[9][10][11]

text: where

text: Speed equation[edit]

text: Since

text: we have[12][13][14]

text: where

text: Torque and speed characteristics[edit]

text: Shunt wound motor[edit]

text: With the shunt wound motor's  high-resistance field winding connected in parallel with the armature, Vm, Rm and Ø are constant such that the no load to full load speed regulation is seldom more than 5%.[15] Speed control is achieved three ways:[16]

text:
Varying the field voltage
Field weakening
Variable resistance in the field circuit.

text: Series wound motor[edit]

text: The series motor responds to increased load by slowing down; the current increases and the torque rises in proportional to the square of the current since the same current flows in both the armature and the field windings. If the motor is stalled, the current is limited only by the total resistance of the windings and the torque can be very high, but there is a danger of the windings becoming overheated. Series wound motors were widely used as traction motors in rail transport[17] of every kind, but are being phased out in favour of power inverter-fed AC induction motors.  The counter EMF aids the armature resistance to limit the current through the armature. When power is first applied to a motor, the armature does not rotate, the counter EMF is zero and the only factor limiting the armature current is the armature resistance.[18] As the prospective current through the armature is very large, the need arises for an additional resistance in series with the armature to limit the current until the motor rotation can build up the counter EMF.  As the motor rotation builds up, the resistance is gradually cut out.

text: The series wound DC motor's most notable characteristic is that it is almost entirely dependent on the torque required to drive the load. This suits large inertial loads as motor accelerates from maximum torque, torque reducing gradually as load increases.

text: As the series motor's speed can be dangerously high, series motors are often geared or direct-connected to the load.[19]

text: Permanent magnet motor[edit]

text: A permanent magnet DC motor is characterized by a linear relationship between stall torque when the torque is maximum with the shaft at standstill and no load speed with no applied shaft torque and maximum output speed . There is a quadratic power relationship between these two speed-axis points.[20]

text: Protection[edit]

text: To extend a DC motor’s service life, protective devices[21] and motor controllers are used to protect it from mechanical damage, excessive moisture, high dielectric stress and high temperature or thermal overloading.[22] These protective devices sense motor fault conditions[23] and either annunciate an alarm to notify the operator or automatically de-energize the motor when a faulty condition occurs. For overloaded conditions, motors are protected with thermal overload relays. Bi-metal thermal overload protectors are embedded in the motor's windings and made from two dissimilar metals. They are designed such that the bimetallic strips will bend in opposite directions when a temperature set point is reached to open the control circuit and de-energize the motor. Heaters are external thermal overload protectors connected in series with the motor’s windings and mounted in the motor contactor. Solder pot heaters melt in an overload condition, which cause the motor control circuit to de-energize the motor. Bimetallic heaters function the same way as embedded bimetallic protectors. Fuses and circuit breakers are overcurrent or short circuit protectors. Ground fault relays also provide overcurrent protection. They monitor the electric current between the motor’s windings and earth system ground. In motor-generators, reverse current relays prevent the battery from discharging and motorizing the generator. Since D.C. motor field loss can cause a hazardous runaway or overspeed condition, loss of field relays[24] are connected in parallel with the motor’s field to sense field current. When the field current decreases below a set point, the relay will deenergize the motor’s armature. A locked rotor condition prevents a motor from accelerating after its starting sequence has been initiated. Distance relays protect motors from locked-rotor faults. Undervoltage motor protection is typically incorporated into motor controllers or starters. In addition, motors can be protected from overvoltages or surges with isolation transformers, power conditioning equipment, MOVs, arresters and harmonic filters. Environmental conditions, such as dust, explosive vapors, water, and high ambient temperatures, can adversely affect the operation of a DC motor. To protect a motor from these environmental conditions, the National Electrical Manufacturers Association (NEMA) and the International Electrotechnical Commission (IEC) have standardized motor enclosure[25] designs based upon the environmental protection they provide from contaminants.  Modern software can also be used in the design stage, such as Motor-CAD, to help increase the thermal efficiency of a motor.

text: DC motor starters[edit]

text: The counter-emf aids the armature resistance to limit the current through the armature. When power is first applied to a motor, the armature does not rotate. At that instant the counter-emf is zero and the only factor limiting the armature current is the armature resistance and inductance. Usually the armature resistance of a motor is less than 1 Ω; therefore the current through the armature would be very large when the power is applied. This current can make an excessive voltage drop affecting other equipment in the circuit and even trip overload protective devices.

text: Therefore, the need arises for an additional resistance in series with the armature to limit the current until the motor rotation can build up the counter-emf. As the motor rotation builds up, the resistance is gradually cut out.

text: Manual-starting rheostat[edit]

text: When electrical and DC motor technology was first developed, much of the equipment was constantly tended by an operator trained in the management of motor systems. The very first motor management systems were almost completely manual, with an attendant starting and stopping the motors, cleaning the equipment, repairing any mechanical failures, and so forth.

text: The first DC motor-starters were also completely manual, as shown in this image. Normally it took the operator about ten seconds to slowly advance the rheostat across the contacts to gradually increase input power up to operating speed. There were two different classes of these rheostats, one used for starting only, and one for starting and speed regulation. The starting rheostat was less expensive, but had smaller resistance elements that would burn out if required to run a motor at a constant reduced speed.

text: This starter includes a no-voltage magnetic holding feature, which causes the rheostat to spring to the off position if power is lost, so that the motor does not later attempt to restart in the full-voltage position. It also has overcurrent protection that trips the lever to the off position if excessive current over a set amount is detected.[26]

text: Three-point starter[edit]

text: The incoming power is indicated as L1 and L2.[where?] The components within the broken lines form the three-point starter. As the name implies there are only three connections to the starter. The connections to the armature are indicated as A1 and A2. The ends of the field (excitement) coil are indicated as F1 and F2. In order to control the speed, a field rheostat is connected in series with the shunt field. One side of the line is connected to the arm of the starter (represented by an arrow in the diagram). The arm is spring-loaded so, it will return to the "Off" position when not held at any other position.

text:
On the first step of the arm, full line voltage is applied across the shunt field. Since the field rheostat is normally set to minimum resistance, the speed of the motor will not be excessive; additionally, the motor will develop a large starting torque.
The starter also connects an electromagnet in series with the shunt field. It will hold the arm in position when the arm makes contact with the magnet.
Meanwhile, that voltage is applied to the shunt field, and the starting resistance limits the current to the armature.
As the motor picks up speed counter-emf is built up; the arm is moved slowly to short.

text: Four-point starter[edit]

text: The four-point starter eliminates the drawback of the three-point starter. In addition to the same three points that were in use with the three-point starter, the other side of the line, L1, is the fourth point brought to the starter when the arm is moved from the "Off" position.  The coil of the holding magnet is connected across the line. The holding magnet and starting resistors function identical as in the three-point starter.

text: The possibility of accidentally opening the field circuit is quite remote. The four-point starter provides the no-voltage protection to the motor. If the power fails, the motor is disconnected from the line.


document_title: List of Sahitya Akademi Award winners for Hindi

question_text: who has won the 2016 sahitya akademi bal puraskar award

text: Recipients[edit]

text:
Year
Author
Work
Type of Work

1955
Makhanlal Chaturvedi
Him Tarangini
Poetry

1956
Vasudeva Saran Agrawal
Padmavat Sanjivani Vyakhya
Commentary

1957
Acharya Narendra Devi
Bauddha Dharma Darshan
Philosophy

1958
Rahul Sankrityayan
Madhya Asia Ka Itihas
History

1959
Ramdhari Singh 'Dinkar'
Sanskriti Ke Char Adhyayay
A survey of Indian culture

1960
Sumitranandan Pant
Kala aur Burha Chand
Poetry

1961
Bhagwati Charan Verma
Bhoole Bisre Chitra
Novel

1962
No Award

1963
Amrit Rai
Premchand: Kalam Ka Sipahi
Biography

1964
S.H. Vatsyayan 'Agyeya'
Aangan Ke Par Dvar
Poetry

1965
Nagendra
Rasa Siddhanta
Treatise on poetics

1966
Jainendra Kumar
Muktibodh
Novelette

1967
Amritlal Nagar
Amrit Aur Vish
Novel

1968
Harivansh Rai Bachchan
Do Chattanen
Poetry

1969
Shrilal Shukla
Raag Darbari
Novel

1970
Ram Vilas Sharma
Nirala Ki Sahitya Sadhana
Biography

1971
Namwar Singh
Kavita Ke Naye Pratiman
Literary criticism

1972
Bhawani Prasad Mishra
Buni Huyi Rassi
Poetry

1973
Hazari Prasad Dwivedi
Alok Parva
Essays

1974
Shivmangal Singh 'Suman'
Mitti Ki Baraat
Poetry

1975
Bhisham Sahni
Tamas
Novel

1976
Yashpal
Meri Teri Uski Baat
Novel

1977
Shamsher Bahadur Singh
Chuka Bhi Hun Nahin Main
Poetry

1978
Bharat Bhushan Agarwal
Utna Vah Suraj Hai
Poetry

1979
Sudama Pandey
Kal Sunana Mujhe
Poetry

1980
Krishna Sobti
Zindaginama - Zinda Rukh
Novel

1981
Trilochan
Tap Ke Taye Hue Din
Novel

1982
Harishankar Parsai
Viklang Shraddha Ka Daur
Satire

1983
Sarveshwar Dayal Saxena
Khutiyon Par Tange Log
Poetry

1984
Raghuvir Sahay
Log Bhool Gaye Hain
Poetry

1985
Nirmal Verma
Kavve Aur Kala Pani
Short stories

1986
Kedarnath Agarwal
Apurva
Poetry

1987
Shrikant Verma
Magadh
Poetry

1988
Naresh Mehta
Aranya
Poetry

1989
Kedarnath Singh
Akaal Mein Saras
Poetry

1990
Shiv Prasad Singh
Neela Chand
Novel

1991
Girija Kumar Mathur
Main Vaqt Ke Hun Samne
Poetry

1992
Giriraj Kishore
Dhai Ghar
Novel

1993
Vishnu Prabhakar
Ardhanarishwar
Novel

1994
Ashok Vajpeyi
Kahin Nahin Wahin
Poetry

1995
Kunwar Narayan
Koi Doosra Nahin
Poetry

1996
Surendra Verma
Mujhe Chand Chahiye
Novel

1997
Leeladhar Jagoori
Anubhav Ke Aakash Mein Chand
Poetry

1998
Arun Kamal
Naye Ilake Mein
Poetry

1999
Vinod Kumar Shukla
Deewar Main Ek Khirkee Rahathi Thi
Novel

2000
Manglesh Dabral
Hum Jo Dekhte Hain
Poetry

2001
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document_title: Geiger–Marsden experiment

question_text: who discovered that most of an atom is empty space

text: Geiger–Marsden experiment

text: Summary[edit]

text: Contemporary theories of atomic structure[edit]

text: The popular theory of atomic structure at the time of Rutherford's experiment was the "plum pudding model". This model was devised by Lord Kelvin and further developed by J. J. Thomson. Thomson was the scientist who discovered the electron, and that it was a component of every atom. Thomson believed the atom was a sphere of positive charge throughout which the electrons were distributed, a bit like plums in a Christmas pudding. The existence of protons and neutrons was unknown at this time. They knew atoms were very tiny (Rutherford assumed they were in the order of 10−8 m in radius[1]). This model was based entirely on classical (Newtonian) physics; the current accepted model uses quantum mechanics.

text: Thomson's model was not universally accepted even before Rutherford's experiments. Thomson himself was never able to develop a complete and stable model of his concept. A Japanese scientist named Hantaro Nagaoka rejected Thomson's model on the grounds that opposing charges cannot penetrate each other.[2] He proposed instead that electrons orbit the positive charge like the rings around Saturn.[3]

text: Implications of the plum pudding model[edit]

text: An alpha particle is a sub-microscopic, positively charged particle of matter. According to Thomson's model, if an alpha particle were to collide with an atom, it would just fly straight through, its path being deflected by at most a fraction of a degree. At the atomic scale, the concept of "solid matter" is meaningless, so the alpha particle would not bounce off the atom like a marble; it would be affected only by the atom's electric fields, and Thomson's model predicted that the electric fields in an atom are just too weak to affect a passing alpha particle much (alpha particles tend to move very fast). Both the negative and positive charges within the Thomson atom are spread out over the atom's entire volume. According to Coulomb's Law, the less concentrated a sphere of electric charge is, the weaker its electric field at its surface will be.[4][5]

text: As a worked example, consider an alpha particle passing tangentially to a Thomson gold atom, where it will experience the electric field at its strongest and thus experience the maximum deflection θ. Since the electrons are very light compared to the alpha particle, their influence can be neglected[6] and the atom can be seen as a heavy sphere of positive charge.

text: Using classical physics, the alpha particle's lateral change in momentum Δp can be approximated using the impulse of force relationship and the Coulomb force expression:

text: The above calculation is but an approximation of what happens when an alpha particle comes near a Thomson atom, but it is clear that the deflection at most will be in the order of a small fraction of a degree. If the alpha particle were to pass through a gold foil some 400 atoms thick and experience maximal deflection in the same direction (unlikely), it would still be a small deflection.

text: The outcome of the experiments[edit]

text: At Rutherford's behest, Geiger and Marsden performed a series of experiments where they pointed a beam of alpha particles at a thin foil of metal and measured the scattering pattern by using a fluorescent screen. They spotted alpha particles bouncing off the metal foil in all directions, some right back at the source. This should have been impossible according to Thomson's model; the alpha particles should have all gone straight through. Obviously, those particles had encountered an electrostatic force far greater than Thomson's model suggested they would, which in turn implied that the atom's positive charge was concentrated in a much tinier volume than Thomson imagined.[7]

text: When Geiger and Marsden shot alpha particles at their metal foils, they noticed only a tiny fraction of the alpha particles were deflected by more than 90°. Most just flew straight through the foil. This suggested that those tiny spheres of intense positive charge were separated by vast gulfs of empty space.[7] Most particles passed through the empty space and experienced negligible deviation, while a handful struck the nuclei of the atoms and bounced right back.

text: Rutherford thus rejected Thomson's model of the atom, and instead proposed a model where the atom consisted of mostly empty space, with all its positive charge concentrated in its center in a very tiny volume, surrounded by a cloud of electrons.

text: Timeline[edit]

text: Background[edit]

text: Ernest Rutherford was a physics professor at the University of Manchester. He had already received numerous honors for his studies of radiation. He had discovered the existence of alpha rays, beta rays, and gamma rays, and had proved that these were the consequence of the disintegration of atoms. In 1906, he received a visit from a German physicist named Hans Geiger, and was so impressed that he asked Geiger to stay and help him with his research.[8] Ernest Marsden was a physics undergraduate student studying under Geiger.

text: Alpha particles are tiny, positively charged particles that are spontaneously emitted by certain substances such as uranium and radium. Rutherford himself had discovered them in 1899. In 1908 he was trying to precisely measure their charge-to-mass ratio. To do this, he first needed to know just how many alpha particles his sample of radium was giving off (after which he would measure their total charge and divide one by the other). Alpha particles are too tiny to be seen even with a microscope, but Rutherford knew that alpha particles ionize air molecules, and if the air is within an electric field, the ions will produce an electric current. On this principle, Rutherford and Geiger designed a simple counting device which consisted of two electrodes in a glass tube. Every alpha particle that passed through the tube would create a pulse of electricity that could be counted. It was an early version of the Geiger counter.[8]

text: The counter that Geiger and Rutherford built proved unreliable because the alpha particles were being too strongly deflected by their collisions with the molecules of air within the detection chamber. The highly variable trajectories of the alpha particles meant that they did not all generate the same number of ions as they passed through the gas, thus producing erratic readings. This puzzled Rutherford because he had thought that alpha particles were just too heavy to be deflected so strongly. Rutherford asked Geiger to investigate just how much matter could scatter alpha rays.[9]

text: The experiments they designed involved bombarding a metal foil with alpha particles to observe how the foil scattered them in relation to their thickness and material. They used a fluorescent screen to measure the trajectories of the particles. Each impact of an alpha particle on the screen produced a tiny flash of light. Geiger worked in a darkened lab for hours on end, counting these tiny scintillations using a microscope.[5] Rutherford lacked the endurance for this work, which is why he left it to his younger colleagues.[10] For the metal foil, they tested a variety of metals, but they preferred gold because they could make the foil very thin, as gold is very malleable.[11] As a source of alpha particles, Rutherford's substance of choice was radium, a substance several million times more radioactive than uranium.

text: The 1908 experiment[edit]

text: A 1908 paper by Geiger, On the Scattering of α-Particles by Matter,[12] describes the following experiment. He constructed a long glass tube, nearly two meters in length. At one end of the tube was a quantity of "radium emanation" (R) that served as a source of alpha particles. The opposite end of the tube was covered with a phosphorescent screen (Z). In the middle of the tube was a 0.9 mm-wide slit. The alpha particles from R passed through the slit and created a glowing patch of light on the screen. A microscope (M) was used to count the scintillations on the screen and measure their spread. Geiger pumped all the air out of the tube so that the alpha particles would be unobstructed, and they left a neat and tight image on the screen that corresponded to the shape of the slit. Geiger then allowed some air in the tube, and the glowing patch became more diffuse. Geiger then pumped out the air and placed some gold foil over the slit at AA. This too caused the patch of light on the screen to become more spread out. This experiment demonstrated that both air and solid matter could markedly scatter alpha particles. The apparatus, however, could only observe small angles of deflection. Rutherford wanted to know if the alpha particles were being scattered by even larger angles—perhaps larger than 90°.

text: The 1909 experiment[edit]

text: In a 1909 paper, On a Diffuse Reflection of the α-Particles,[13] Geiger and Marsden described the experiment by which they proved that alpha particles can indeed be scattered by more than 90°. In their experiment, they prepared a small conical glass tube (AB) containing "radium emanation" (radon), "radium A" (actual radium), and "radium C" (bismuth-214); its open end sealed with mica. This was their alpha particle emitter. They then set up a lead plate (P), behind which they placed a fluorescent screen (S). The tube was held on the opposite side of plate, such that the alpha particles it emitted could not directly strike the screen. They noticed a few scintillations on the screen, because some alpha particles got around the plate by bouncing off air molecules. They then placed a metal foil (R) to the side of the lead plate. They pointed the tube at the foil to see if the alpha particles would bounce off it and strike the screen on the other side of the plate, and observed an increase in the number of scintillations on the screen. Counting the scintillations, they observed that metals with higher atomic mass, such as gold, reflected more alpha particles than lighter ones such as aluminium.

text: Geiger and Marsden then wanted to estimate the total number of alpha particles that were being reflected. The previous setup was unsuitable for doing this because the tube contained several radioactive substances (radium plus its decay products) and thus the alpha particles emitted had varying ranges, and because it was difficult for them to ascertain at what rate the tube was emitting alpha particles. This time, they placed a small quantity of radium C (bismuth-214) on the lead plate, which bounced off a platinum reflector (R) and onto the screen. They found that only a tiny fraction of the alpha particles that struck the reflector bounced onto the screen (in this case, 1 in 8000).[13]

text: The 1910 experiment[edit]

text: A 1910 paper[14] by Geiger, The Scattering of the α-Particles by Matter, describes an experiment by which he sought to measure how the most probable angle through which an a-particle is deflected varies with the material it passes through, the thickness of said material, and the velocity of the alpha particles. He constructed an airtight glass tube from which the air was pumped out. At one end was a bulb (B) containing "radium emanation" (radon-222). By means of mercury, the radon in B was pumped up the narrow glass pipe whose end at A was plugged with mica. At the other end of the tube was a fluorescent zinc sulfide screen (S). The microscope which he used to count the scintillations on the screen was affixed to a vertical millimeter scale with a vernier, which allowed Geiger to precisely measure where the flashes of light appeared on the screen and thus calculate the particles' angles of deflection. The alpha particles emitted from A was narrowed to a beam by a small circular hole at D. Geiger placed a metal foil in the path of the rays at D and E to observe how the zone of flashes changed. He could also vary the velocity of the alpha particles by placing extra sheets of mica or aluminium at A.

text: From the measurements he took, Geiger came to the following conclusions:

text:
the most probable angle of deflection increases with the thickness of the material
the most probable angle of deflection is proportional to the atomic mass of the substance
the most probable angle of deflection decreases with the velocity of the alpha particles
the probability that a particle will be deflected by more than 90° is vanishingly small

text: Rutherford mathematically models the scattering pattern[edit]

text: Considering the results of the above experiments, Rutherford published a landmark paper in 1911 titled "The Scattering of α and β Particles by Matter and the Structure of the Atom" wherein he proposed that the atom contains at its center a volume of electric charge that is very small and intense (in fact, Rutherford treats it as a point charge in his calculations).[1] For the purpose of his mathematical calculations he assumed this central charge was positive, but he admitted he could not prove this and that he had to wait for other experiments to develop his theory.

text: Rutherford developed a mathematical equation that modeled how the foil should scatter the alpha particles if all the positive charge and most of the atomic mass was concentrated in a single point at the center of an atom.

text:
s
=

X
n
t

csc

4

ϕ
2

16

r

2

⋅
(

2

Q

n

Q

α

m

v

2

)

2

{\displaystyle s={\frac {Xnt\csc ^{4}{\tfrac {\phi }{2}}}{16r^{2}}}\cdot ({\frac {2Q_{n}Q_{\alpha }}{mv^{2}}})^{2}}

text: From the scattering data, Rutherford estimated the central charge Qn to be about +100 units (see Rutherford model)

text: The 1913 experiment[edit]

text: In a 1913 paper, The Laws of Deflexion of α Particles through Large Angles,[15] Geiger and Marsden describe a series of experiments by which they sought to experimentally verify the above equation that Rutherford developed. Rutherford's equation predicted that the number of scintillations per minute s that will be observed at a given angle Φ should be proportional to:

text:
csc4Φ/2
thickness of foil t
magnitude of central charge Qn
1/(mv2)2

tag: ol

text: Their 1913 paper describes four experiments by which they proved each of these four relationships.

text: To test how the scattering varied with the angle of deflection (i.e. if s ∝ csc4Φ/2) Geiger and Marsden built an apparatus that consisted of a hollow metal cylinder mounted on a turntable. Inside the cylinder was a metal foil (F) and a radiation source containing radon (R), mounted on a detached column (T) which allowed the cylinder to rotate independently. The column was also a tube by which air was pumped out of the cylinder. A microscope (M) with its objective lens covered by a fluorescent zinc sulfide screen (S) penetrated the wall of the cylinder and pointed at the metal foil. By turning the table, the microscope could be moved a full circle around the foil, allowing Geiger to observe and count alpha particles deflected by up to 150°. Correcting for experimental error, Geiger and Marsden found that the number of alpha particles that are deflected by a given angle Φ is indeed proportional to csc4Φ/2.[15]

text: Geiger and Marsden then tested how the scattering varied with the thickness of the foil (i.e. if s ∝ t). They constructed a disc (S) with six holes drilled in it. The holes were covered with metal foil (F) of varying thickness, or none for control. This disc was then sealed in a brass ring (A) between two glass plates (B and C). The disc could be rotated by means of a rod (P) to bring each window in front of the alpha particle source (R). On the rear glass pane was a zinc sulfide screen (Z). Geiger and Marsden found that the number of scintillations that appeared on the zinc sulfide screen was indeed proportional to the thickness as long as said thickness was small.[15]

text: Geiger and Marsden reused the above apparatus to measure how the scattering pattern varied with the square of the nuclear charge (i.e. if s ∝ Qn2). Geiger and Marsden didn't know what the positive charge of the nucleus of their metals were (they had only just discovered the nucleus existed at all), but they assumed it was proportional to the atomic weight, so they tested whether the scattering was proportional to the atomic weight squared. Geiger and Marsden covered the holes of the disc with foils of gold, tin, silver, copper, and aluminum. They measured each foil's stopping power by equating it to an equivalent thickness of air. They counted the number of scintillations per minute that each foil produced on the screen. They divided the number of scintillations per minute by the respective foil's air equivalent, then divided again by the square root of the atomic weight (Geiger and Marsden knew that for foils of equal stopping power, the number of atoms per unit area is proportional to the square root of the atomic weight). Thus, for each metal, Geiger and Marsden obtained the number of scintillations that a fixed number of atoms produce. For each metal, they then divided this number by the square of the atomic weight, and found that the ratios were more or less the same. Thus they proved that s ∝ Qn2.[15]

text: Finally, Geiger and Marsden tested how the scattering varied with the velocity of the alpha particles (i.e. if s ∝ 1/v4). Using the same apparatus again, they slowed the alpha particles by placing extra sheets of mica in front of the alpha particle source. They found that, within the range of experimental error, that the number of scinitillations was indeed proportional to 1/v4.[15]

text: Rutherford determines the nucleus is positively charged[edit]

text: In his 1911 paper (see above), Rutherford assumed that the central charge of the atom was positive, but a negative charge would have fitted his scattering model just as well.[16] In a 1913 paper,[17] Rutherford declared that the "nucleus" (as he now called it) was indeed positively charged, based on the result of experiments exploring the scattering of alpha particles in various gases.

text: In 1917, Rutherford and his assistant William Kay began exploring the passage of alpha particles through gases such as hydrogen and nitrogen. In an experiment where they shot a beam of alpha particles through hydrogen, the alpha particles knocked the hydrogen nuclei forwards in the direction of the beam, not backwards. In an experiment where they shot alpha particles through nitrogen, he discovered that the alpha particles knocked hydrogen nuclei (i.e. protons) out of the nitrogen nuclei.[16]

text: Legacy[edit]

text: When Geiger reported to Rutherford that he had spotted alpha particles being strongly deflected, Rutherford was astounded. In a lecture Rutherford delivered at Cambridge University, he said:

text: It was quite the most incredible event that has ever happened to me in my life. It was almost as incredible as if you fired a 15-inch shell at a piece of tissue paper and it came back and hit you. On consideration, I realized that this scattering backward must be the result of a single collision, and when I made calculations I saw that it was impossible to get anything of that order of magnitude unless you took a system in which the greater part of the mass of the atom was concentrated in a minute nucleus. It was then that I had the idea of an atom with a minute massive centre, carrying a charge.

text: Accolades soon flooded in. Hantaro Nagaoka, who had once proposed a Saturnian model of the atom, wrote to Rutherford from Tokyo in 1911: "Congratulations on the simpleness of the apparatus you employ and the brilliant results you obtained". The conclusions of these experiments revealed how all matter on Earth is structured and thus affected every scientific and engineering discipline, making it one of the most pivotal scientific discoveries of all time. The astronomer Arthur Eddington called Rutherford's discovery the most important scientific achievement since Democritus proposed the atom ages earlier.[10]

text: Like most scientific models, Rutherford's atomic model was neither perfect nor complete. According to classical Newtonian physics, it was in fact impossible. Accelerating charged particles radiate electromagnetic waves, so an electron orbiting an atomic nucleus in theory would spiral into the nucleus as it loses energy. To fix this problem, scientists had to incorporate quantum mechanics into Rutherford's model.