Electric charge

These phenomena were investigated in the late eighteenth century by Charles-Augustin de Coulomb, who deduced that charge manifests itself in two opposing forms. The magnitude of the electromagnetic force, whether attractive or repulsive, is given by Coulomb’s law, which relates the force to the product of the charges and has an inverse-square relation to the distance between them.

In comparison with the much weaker gravitational force, the electromagnetic force pushing two electrons apart is 1042 times that of the gravitational attraction pulling them together.

Charge originates from certain types of subatomic particles, the most familiar carriers of which are the electron proton. Electric charge gives rise to and interacts with the electromagnetic force, one of the four fundamental forces of nature. Experiment has shown charge to be a conserved quantity, that is, the net charge within an electrically isolated system will always remain constant regardless of any changes taking place within that system.

By convention, the charge carried by electrons is deemed negative, and that by protons positive, a custom that originated with the work of Benjamin Franklin The amount of charge is usually given the symbol Q and expressed in coulombs each electron carries the same charge of approximately −1.6022×10−19 coulomb. Charge is possessed not just by matter, but also by antimatter antiparticle bearing an equal and opposite charge to its corresponding particle.

:3 An electric field is created whenever there is a difference in potential energy across some boundary separating regions where different amounts of electrical charge reside. For example, consider a sphere containing both positively and negatively charged ions. When the sphere is placed into water, the positively charged ions become immersed while the negatively charged ones remain above the surface. As a result, the region inside the sphere becomes more highly charged than outside, creating an electric field around the sphere.  

Electric current

The movement of electric charge is known as an electric current, the intensity of which is usually measured in amperes. Electric current can flow through some things, electrical conductors, but will not flow through an electrical insulator By historical convention, a positive current is defined as having the same direction of flow as any positive charge it contains, or to flow from the most positive part of a circuit to the most negative part. Current defined in this manner is called conventional current. The motion of negatively charged electrons around an electric circuit, one of the most familiar forms of current, is thus deemed positive in the opposite direction to that of the electrons.

electric arc provides an energetic demonstration of electric current The process by which electric current passes through a material is termed electrical conduction, and its nature varies with that of the charged particles and the material through which they are travelling. While the particles themselves can move quite slowly, sometimes with an average drift velocity only fractions of a millimetre per second, electric field that drives them itself propagates at close to the speed of light, enabling electrical signals to pass rapidly along wires.

in 1800, a process now known as electrolysis. He had discovered electromagnetism, a fundamental interaction between electricity and magnetics. The level of electromagnetic emissions generated by electric arcing is high enough to produce electromagnetic interference, which can be detrimental to the workings of adjacent equipment.

Alternating current is affected by electrical properties that are not observed under steady state direct current, such as inductance capacitance :223–25 These properties however can become important when circuitry is subjected to transients, such as when first energised.

Current is also classified according to other physical characteristics, including type, magnitude, and frequency. Type refers to whether the current flows continuously or periodically. Magnitude describes the amount of power delivered by the current. Frequency measures the number of cycles completed each unit of time. For instance, 60 Hz AC has a frequency of 0.5 cycle/second, whereas 50 Hz AC has a frequency twice as great, 1 cycle/second. In practice, all three types may vary simultaneously.

Electric field

The concept of the electric field was introduced by Michael Faraday. The electric field acts between two charges in a similar manner to the way that the gravitational field acts between two masses, and like it, extends towards infinity and shows an inverse square relationship with distance.

An electric field is defined as the strength of the interaction between two point-like sources of opposite sign separated by some distance r. It has units of newtons per coulomb and its magnitude depends upon the number of electrons present in each source. For example, if we have one electron located near the origin and another nearby, then their combined electrostatic potential energy will be proportional to 1/.  

Electric potential

A pair of AA cells. A small charge placed within an electric field experiences a force, and to have brought that charge to that point against the force requires work. It is usually measured in volts, and one volt is the potential for which one joule of work must be expended to bring a charge of one coulomb :494–98 This definition of potential, while formal, has little practical application, and a more useful concept is that of electric potential difference, and is the energy required to move a unit charge between two specified points. An electric field has the special property that it is conservative, which means that the path taken by the test charge is irrelevant: all paths between two specified points expend the same energy, and thus a unique value for potential difference may be stated.

This reference point naturally takes the name earth ground. Electric potential is a scalar quantity, that is, it has only magnitude and not direction. They must also lie parallel to a conductor’s surface, otherwise this would produce a force that will move the charge carriers to even the potential of the surface.

In physics, electricity or electromagnetism are physical phenomena involving charges moving under the influence of forces. In classical mechanics, these forces can be described using Newton’s laws of motion; however, when dealing with electrical systems, such as circuits, Maxwell’s equations provide a better model. These describe how electromagnetic fields behave, including their effects on matter. Electricity is often used synonymously with magnetism, although they are distinct concepts.  

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