Electric Charge


Read here about a physical property that can be measured and depicted in a scalometer.

Overview

Electric charge is a physical property of matter which causes it to experience a force when near other electrically charged matter. Electric charge comes in two types, called positive and negative. Two positively charged substances, or objects, experience a mutual repulsive force, as do two negatively charged objects. Positively charged objects and negatively charged objects experience an attractive force.

Units of Electric Charge


Units of electric current

The ampere is an SI base unit. It is defined as that constant current which, if maintained in two straight parallel
conductors of infinite length, of negligible circular cross-section, and placed
1 metre apart in vacuum, would produce between these conductors a force equal to
2 x 10-7 newton per metre of length.

Electric current is a flow of electric charge through a medium. This charge is typically carried by moving electrons in a conductor such as wire. It can also be carried by ions in an electrolyte, or by both ions and electrons in a plasma. The SI unit for measuring the rate of flow of electric charge is the ampere, which is charge flowing through some surface at the rate of one coulomb per second. Electric current is measured using an ammeter.

The minimum electric current is zero, though this theoretical limit is approached and not achieved.

There is no theoretically maximum electric current.

Units of electric charge

The SI unit of electric charge is the coulomb (C), although in electrical engineering it is also common to use the ampere-hour (Ah).

The electric charge is a fundamental conserved property of some subatomic particles, which determines their electromagnetic interaction. Electrically charged matter is influenced by, and produces, electromagnetic fields. The interaction between a moving charge and an electromagnetic field is the source of the electromagnetic force, which is one of the four fundamental forces.

The minimum electric charge is the elementary charge, e, approximately equal to 1.602×10^−19 coulombs (except for particles called quarks which have charges that are multiples of ⅓e). The proton has a charge of e, and the electron has a charge of −e. There is a minimum charge since the charge is quantized; that is, it comes in multiples of individual small units.

There is no known maximum electric charge.

Units of Conductance

Conductance is a measure of how easily electricity flows along a certain path. The inverse of conductance is resistance, an indication of a material's opposition to the passage of an electric current. Conductance shares some conceptual parallels with the mechanical notion of friction. An object of uniform cross section has a conductance proportional to its cross-sectional area and inversely proportion to its length. The SI unit of electrical conductance is the siemens (S).

There is no maximum conductance, as a superconductor has infinite conductivity.

There is a theoretical minimum conductance of zero, where no electric current is passed.

Units of Resistance

The electrical resistance of an electrical element measures its opposition to the passage of an electric current; the inverse quantity is electrical conductance, measuring how easily electricity flows along a certain path. Electrical resistance shares some conceptual parallels with the mechanical notion of friction.

The SI unit of electrical resistance is the ohm (Ω), while electrical conductance is measured in siemens (S). The ohm is defined as potential emf per ampere, or volts per ampere (V/A).

An object of uniform cross section has a resistance proportional to its resistivity and length and inversely proportional to its cross-sectional area. All materials show some resistance, except for superconductors, which have a resistance of zero.

The resistance of an object is defined as the ratio of voltage across it to current through it: R = V over I, or voltage over amperage.

For a wide variety of materials and conditions, the electrical resistance R is constant for a given temperature; it does not depend on the amount of current through or the potential difference (voltage) across the object. Such materials are called Ohmic materials. For objects made of ohmic materials the definition of the resistance, with R being a constant for that resistor, is known as Ohm's law.

There is no maximum resistance, as there is a theoretical scenario where absolutely no current passes between materials.

The minimum resistance is zero, being the resistance of a superconductor that displays no known impediment to the flow of electrons.

Units of Capacitance

In electromagnetism and electronics, capacitance is the ability of a body to hold an electrical charge. Capacitance is also a measure of the amount of electrical energy stored (or separated) for a given electric potential. The SI unit of capacitance is the farad; 1 farad is 1 coulomb per volt.

The minimum capacitance is zero, indicating that the body cannot hold electric charge. This is a theoretical limit, as every material can store some electrons.

There is no theoretical maximum capacitance.

Units of Electromotive Force

In physics, electromotive force, or most commonly emf (seldom capitalized), or (occasionally) electromotance is defined by Langmuir as "that which tends to cause current (actual electrons and ions) to flow." More formally, emf is the external work expended per unit of charge to produce an electric potential difference across two open-circuited terminals. The electric potential difference is created by separating positive and negative charges, thereby generating an electric field. The created electrical potential difference drives current flow if a circuit is attached to the source of emf. When current flows, however, the voltage across the terminals of the source of emf is no longer the open-circuit value, due to voltage drops inside the device due to its internal resistance.

Devices that can provide emf include voltaic cells, thermoelectric devices, solar cells, electrical generators, transformers, and even Van de Graaff generators. In nature, emf is generated whenever magnetic field fluctuations occur through a surface. An example for this is the varying Earth magnetic field during a geomagnetic storm, acting on anything on the surface of the planet, like an extended electrical grid.

The volt (symbol: V) is the SI derived unit of electromotive force, commonly called "voltage". It is also the unit for the related but slightly different quantity electric potential in a point (voltage as related to a reference ground) and electric potential difference (also called "electrostatic potential difference"). Potential emf is watts per ampere (W/A).

There is no known maximum emf.

The minimum emf is zero, indicating that no electrical force is exerted. This is a theoretical limit, as there is always some difference in charge between materials.