The study of fields and potentials due to stationary electric charges. Electrostatic forces bind electrons to the nucleus in atoms.
| Electromagnetism | |
| Magnetism | |
| Electrostatics | |
|---|---|
| Electric charge | |
| Coulomb's law | |
| Electric field | |
| Gauss's law | |
| Electric potential | |
| Magnetostatics | |
| Ampere's law | |
| Magnetic field | |
| Magnetic moment | |
| Electrodynamics | |
| Electric current | |
| Lorentz force law | |
| Electromotive force | |
| Electromagnetic induction | |
| Faraday-Lenz law | |
| Displacement current | |
| Maxwell's equations | |
| Electromagnetic field | |
| Electromagnetic radiation | |
| Electrical circuits | |
| Electrical conduction | |
| Electrical resistance | |
| Capacitance | |
| Inductance | |
| Impedance | |
| Resonant cavities | |
| Waveguides | |
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Electrostatics is the branch of physics that deals with the forces exerted by a static (i.e. unchanging) electric field upon charged objects. In electrostatics we study e-fields, voltage, and charge, but ignore any magnetic fields generated by the motion of these charges or that may be present for other reasons.
The electrostatic approximation
The validity of the electrostatic approximation rests on the assumption that the electric field is irrotational:
From Faraday's law, this assumption implies the absence or near-absence of time-varying magnetic fields:
In other words, electrostatics does not require the absence of magnetic fields or electric currents.
Electrostatic potential
Because the electric field is irrotational, it is possible to express the electric field as the gradient of a scalar function, called the electrostatic potential (also known as the voltage). Thus, the electrostatic potential Φ is related to the electric field E by the equation:
Fundamental concepts
Coulomb's law
The fundamental equation of electrostatics is Coulomb's law, which describes the force between two point charges:
The electric field
The electric field (in units of volts per meter) is defined as the force (in newtons) per unit charge (in coulombs). From this definition and Coulomb's law, it follows that the magnitude of the electric field E created by a single point charge Q is:
Gauss's law
Gauss' law states that "the total electric flux through a closed surface is proportional to the total electric charge enclosed within the surface."
Mathematically, Gauss's law takes the form of an integral equation:
Alternatively, in differential form, the equation becomes
Poisson's equation
The definition of electrostatic potential, combined with the differential form of Gauss's law (above), provides a relationship between the potential Φ and the charge density ρ:
This relationship is a form of Poisson's equation.
Laplace's equation
In the absence of unpaired electric charge, the equation becomes
which is Laplace's equation.
Static charge generation
Charge separation by contact
The presence of surface charge imbalance means that the objects will exhibit attractive or repulsive forces. This surface charge imbalance, which leads to static electricity, can be generated by touching two differing surfaces together and then separating them due to the phenomena of contact electrification and the triboelectric effect.
Triboelectric series
The triboelectric effect is a type of contact electrification in which certain materials become electrically charged when coming into contact with another, different, material, and are then separated. Amber, for example, can acquire an electric charge by friction with a material like wool.
Electrostatic generators
The presence of surface charge imbalance means that the objects will exhibit attractive or repulsive forces. This surface charge imbalance, which leads to static electricity, can be generated by touching two differing surfaces together and then separating them due to the phenomena of contact electrification and the triboelectric effect. electronics manufacturing.) When working in direct contact with integrated circuit electronics (especially delicate MOSFETs), or in the presence of flammable gas, care must be taken to avoid accumulating and suddenly discharging a static charge (see electrostatic discharge).
Today we regard static electricity as a subject heading also called Electrostatics: a class of various phenomena associated with substances or objects having a net electric charge.
Note that the charges associated with static electricity need not be still or "static." The presence of charge motions and electric current does not detract from the net charge, the electrostatic forces, nor from the sparking and corona discharge, or other phenomena.
Static electricity is an important element in the biological process of pollination by bees, since the charge on a bee's body helps to attract and hold pollen.
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