Coulombs Law - Coulomb\'s law, or Coulomb\'s inverse-square law, is an experimental law of physics PDF

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Coulomb's law, or Coulomb's inverse-square law, is an experimental law of physics that quantifies the amount of force between two stationary, electrically charged particles. The electric force between charged bodies at rest is conventionally called electrostatic force or Coulomb force. Wikipedia...

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Coulomb's law By: Charles-Augustin

Coulomb’s law, mathematical description of the electric force between charged objects. Formulated by the 18th-century French physicist Charles-Augustin de Coulomb, it is analogous to Isaac Newton’s law of gravity. Both gravitational and electric forces decrease with the square of the distance between the objects, and both forces act along a line between them. In Coulomb’s law, however, the magnitude and sign of the electric force are determined by the electric charge, rather than the mass, of an object. Thus, charge determines how electromagnetism influences the motion of charged objects. Charge is a basic property of matter. Every constituent of matter has an electric charge with a value that can be positive, negative, or zero. For example, electrons are negatively charged, and atomic nuclei are positively charged. Most bulk matter has an equal amount of positive and negative charge and thus has zero net charge. According to Coulomb, the electric force for charges at rest has the following properties: 1. 2.

Like charges repel each other; unlike charges attract. Thus, two negative charges repel one another, while a positive charge attracts a negative charge. The attraction or repulsion acts along the line between the two charges.

3.

The size of the force varies inversely as the square of the distance between the two charges. Therefore, if the distance between the two charges is doubled, the attraction or repulsion becomes weaker, decreasing to one-fourth of the original value. If the charges come 10 times closer, the size of the force increases by a factor of 100.

4.

The size of the force is proportional to the value of each charge. The unit used to measure charge is the coulomb (C). If there were two positive charges, one of 0.1 coulomb and the second of 0.2 coulomb, they would repel each other with a force that depends on the product 0.2 × 0.1. Thus, if each of the charges were reduced by one-half, the repulsion would be reduced to onequarter of its former value.

Electric charge Electric charge, basic property of matter carried by some elementary particles that governs how the particles are affected by an electric or magnetic field. Electric charge, which can be positive or negative, occurs in discrete natural units and is neither created nor destroyed.

Electric charges are of two general types: Positive and Negative. Two objects that have an excess of one type of charge exert a force of repulsion on each other when relatively close together. Two objects that have excess opposite charges, one positively charged and the other negatively charged, attract each other when relatively near. Many fundamental, or subatomic, particles of matter have the property of electric charge. For example, electrons have negative charge and protons have positive charge, but neutrons have zero charge. The negative charge of each electron is found by experiment to have the same magnitude, which is also equal to that of the positive charge of each proton. Charge thus exists in natural units equal to the charge of an electron or a proton, a fundamental physical constant. A direct and convincing measurement of an electron’s charge, as a natural unit of electric charge, was first made (1909) in the Millikan oil-drop experiment. Atoms of matter are electrically neutral because their nuclei contain the same number of protons as there are electrons surrounding the nuclei. Electric current and charged objects involve the separation of some of the negative charge of neutral atoms. Current in metal wires consists of a drift of electrons of which one or two from each atom are more loosely bound than the rest. Some of the atoms in the surface layer of a glass rod positively charged by rubbing it with a silk cloth have lost electrons, leaving a net positive charge because of the un-neutralized protons of their nuclei. A negatively charged object has an excess of electrons on its surface. Electric charge is conserved: in any isolated system, in any chemical or nuclear reaction, the net electric charge is constant. The algebraic sum of the fundamental charges remains the same. The unit of electric charge in the metre–kilogram–second and SI systems is the coulomb and is defined as the amount of electric charge that flows through a cross section of a conductor in an electric circuit during each second when the current has a value of one ampere. One coulomb consists of 6.24 × 1018 natural units of electric charge, such as individual electrons or protons. From the definition of the ampere, the electron itself has a negative charge of 1.602176634 × 10−19 coulomb. An electrochemical unit of charge, the faraday, is useful in describing electrolysis reactions, such as in metallic electroplating. One faraday equals 96485.332123 coulombs, the charge of a mole of electrons (that is, an Avogadro’s number, 6.02214076 × 1023, of electrons).

Coulomb force Coulomb force, also called electrostatic force or Coulomb interaction, attraction or repulsion of particles or objects because of their electric charge. One of the basic physical forces, the electric force is named for a French physicist, Charles-Augustin de Coulomb, who in 1785 published the results of an experimental investigation into the correct quantitative description of this force. Two like electric charges, both positive or both negative, repel each other along a straight line between their centres. Two unlike charges, one positive, one negative, attract each other along a straight line joining their centres. The electric force is operative between charges down to distances of at least

10 metre, or approximately one-tenth of the diameter of atomic nuclei. Because of their positive charge, protons within nuclei repel each other, but nuclei hold together because of another basic physical force, the strong interaction, or nuclear force, which is stronger than the electric force. Massive, but electrically neutral, astronomical bodies such as planets and stars are bound together in solar systems and galaxies by still another basic physical force, gravitation, which though much weaker than the electric force, is always attractive and is the dominant force at great distances. At distances between these extremes, including the distances of everyday life, the only significant physical force is the electric force in its many varieties along with the related magnetic force. The magnitude of the electric force F is directly proportional to the amount of one electric charge, q1, multiplied by the other, q2, and inversely proportional to the square of the distance r between their centres. Expressed in the form of an equation, this relation, called Coulomb’s law, may be written by including the proportionality factor k as F = kq1q2/r2. In the centimetre–gram–second system of units, the proportionality factor k in a vacuum is set equal to 1 and unit electric charge is defined by Coulomb’s law. If an electric force of one unit (one dyne) arises between two equal electric charges one centimetre apart in a vacuum, the amount of each charge is one electrostatic unit, esu , or statcoulomb. In the metre–kilogram–second and the SI systems, the unit of force (newton), the unit of charge (coulomb), and the unit of distance (metre), are all defined independently of Coulomb’s law, so the proportionality factor k is constrained to take a value consistent with these definitions, namely, k in a vacuum equals 8.98 × 109 newton square metre per square coulomb. This choice of value for k permits the practical electrical units, such as ampere and volt, to be included with the common metric mechanical units, such as metre and kilogram, in the same system.

Fundamental force fundamental force, also called fundamental interaction, in physics, any of the four basic forces— gravitational, electromagnetic, strong, and weak—that govern how objects or particles interact and how certain particles decay. All the known forces of nature can be traced to these fundamental forces. The fundamental forces are characterized on the basis of the following four criteria: the types of particles that experience the force, the relative strength of the force, the range over which the force is effective, and the nature of the particles that mediate the force. Gravitation and electromagnetism were recognized long before the discovery of the strong and weak forces because their effects on ordinary objects are readily observed. The gravitational force, described systematically by Isaac Newton in the 17th century, acts between all objects having mass; it causes apples to fall from trees and determines the orbits of the planets around the Sun. The electromagnetic force, given scientific definition by James Clerk Maxwell in the 19th century, is responsible for the repulsion of like and the attraction of unlike electric charges; it also explains the chemical behaviour of matter and the properties of light. The strong and weak forces were discovered by physicists in the 20th century when they finally probed into the core of the atom. The strong force acts between quarks, the constituents of all subatomic particles, including protons and neutrons. The residual

effects of the strong force bind the protons and neutrons of the atomic nucleus together in spite of the intense repulsion of the positively charged protons for each other. The weak force manifests itself in certain forms of radioactive decay and in the nuclear reactions that fuel the Sun and other stars. Electrons are among the elementary subatomic particles that experience the weak force but not the strong force. The four forces are often described according to their relative strengths. The strong force is regarded as the most powerful force in nature. It is followed in descending order by the electromagnetic, weak, and gravitational forces. Despite its strength, the strong force does not manifest itself in the macroscopic universe because of its extremely limited range. It is confined to an operating distance of about 10−metre—about the diameter of a proton. When two particles that are sensitive to the strong force pass within this distance, the probability that they will interact is high. The range of the weak force is even shorter. Particles affected by this force must pass within 10−17 metre of one another to interact, and the probability that they will do so is low even at that distance unless the particles have high energies. By contrast, the gravitational and electromagnetic forces operate at an infinite range. That is to say, gravity acts between all objects of the universe, no matter how far apart they are, and an electromagnetic wave, such as the light from a distant star, travels undiminished through space until it encounters some particle capable of absorbing it. For years physicists have sought to show that the four basic forces are simply different manifestations of the same fundamental force. The most successful attempt at such a unification is the electroweak theory, proposed during the late 1960s by Steven Weinberg, Abdus Salam, and Sheldon Lee Glashow. This theory, which incorporates quantum electrodynamics (the quantum field theory of electromagnetism), treats the electromagnetic and weak forces as two aspects of a more-basic electroweak force that is transmitted by four carrier particles, the so-called gauge bosons. One of these carrier particles is the photon of electromagnetism, while the other three—the electrically charged W+ and W− particles and the neutral Z 0 particle—are associated with the weak force. Unlike the photon, these weak gauge bosons are massive, and it is the mass of these carrier particles that severely limits the effective range of the weak force. In the 1970s investigators formulated a theory for the strong force that is similar in structure to quantum electrodynamics. According to this theory, known as quantum chromodynamics, the strong force is transmitted between quarks by gauge bosons called gluons. Like photons, gluons are massless and travel at the speed of light. But they differ from photons in one important respect: they carry what is called “colour” charge, a property analogous to electric charge. Gluons are able to interact together because of colour charge, which at the same time limits their effective range.

Investigators are seeking to devise comprehensive theories that will unify all four basic forces of nature. So far, however, gravity remains beyond attempts at such unified field theories. The current physical description of the fundamental forces is embodied within the Standard Model of particle physics, which outlines the properties of all the fundamental particles and their forces.

Graphical representations of the effect of fundamental forces on the behaviour of elementary subatomic particles are incorporated in Feynman diagrams....