Definition and Basics of Electric Current
– Electric current is the flow of charged particles through a conductor or space.
– It is defined as the net rate of flow of electric charge through a surface.
– Charge carriers in electric circuits can be electrons, ions, or holes.
– In the International System of Units (SI), electric current is expressed in units of ampere (A).
– The ampere is an SI base unit and electric current is a base quantity in the International System of Quantities (ISQ).
– The conventional symbol for current is ‘I’.
– The symbol originates from the French phrase ‘intensité du courant’ (current intensity).
– The direction of conventional current is defined as the direction in which positive charges flow.
– In conductive materials like metals, electrons are the charge carriers and flow in the opposite direction of conventional current.
– Positive and negative charge carriers can exist simultaneously in certain materials.
– The reference direction of current is usually specified by an arrow on a circuit schematic diagram.
– The actual direction of current through a circuit element is often unknown until the analysis is completed.
– Negative values for current indicate that the actual direction is opposite to the chosen reference direction.
– The reference direction of current is assigned arbitrarily during circuit analysis.
– The direction of current flow depends on the potential difference across the circuit element.
– Ohm’s law states that the current through a conductor is directly proportional to the potential difference across it.
– The equation that describes this relationship is I = V/R, where I is the current, V is the potential difference, and R is the resistance.
– The resistance in this relation is constant and independent of the current.
– Ohm’s law is used to calculate current in a circuit when the potential difference and resistance are known.
– Alternating current (AC) periodically reverses the direction of electric charge movement.
– AC power is commonly used in businesses and residences, with a sine wave being the usual waveform.
– Direct current (DC) refers to the movement of electric charge in only one direction.
– DC is produced by sources like batteries and can be converted from AC using a rectifier.
– Examples of natural and man-made occurrences of electric current include lightning, power lines, and electronic circuits.
Electromagnetism
– Magnetic field produced by electric current in a solenoid
– Coil of wires in an electromagnet behaves like a magnet with current flow
– Coil loses magnetism immediately when current is switched off
– Electric current produces a persistent magnetic field with circular field lines
– Alternating current in solenoid induces electric current in wire loop
– Alternating current in solenoid produces changing magnetic field
– Changing magnetic field induces electromotive force (EMF)
– EMF starts electric current when suitable path is present
– Electromagnetic induction can generate radio waves
– Radio waves travel at the speed of light and can induce electric currents in distant conductors
Conduction mechanisms in various media
– Electric charge flows through metallic solids by means of electrons
– In other media, any stream of charged objects may constitute an electric current
– Conventional current is defined as moving in the same direction as positive charge flow
– Current in conductors can be due to both positive and negative charged particles
– Current in electrolytes is composed of positive and negative ions
– Outer electrons in metals are free to move within the metal lattice
– Conduction electrons in metals serve as charge carriers
– Metals are conductive due to the presence of many free electrons
– Free electrons in metals move randomly due to thermal energy
– When subjected to electric force, free electrons rush in the direction of the force, forming an electric current
– Electric currents in electrolytes are flows of electrically charged particles (ions)
– Sodium and chloride ions move towards opposite electrodes in a solution
– Proton conductors and certain solid electrolytes contain mobile protons
– Electric currents in these materials are composed of moving protons
– Some electrolyte mixtures exhibit visible currents due to brightly colored ions
– Electrical conduction in ordinary gases is via mobile ions produced by various sources
– Gases are dielectrics or insulators due to low electrical conductivity
– Applied electric field can cause breakdown and create a conductive plasma
– Plasma is formed by ionization of electrons from gas molecules or atoms
– Electrons in plasma carry the bulk of the electric current due to their lower mass
– Perfect vacuum normally behaves as a perfect insulator
– Metal electrode surfaces can inject free electrons or ions into a vacuum
– Field electron emission and thermionic emission can make a vacuum conductive
– Thermionic emission occurs when thermal energy exceeds the metal’s work function
– Field electron emission occurs when electric field causes electrons to be emitted from a surface
Superconductivity and Semiconductors
– Superconductivity is a phenomenon of zero electrical resistance and expulsion of magnetic fields.
– It was discovered by Heike Kamerlingh Onnes in 1911.
– Superconductivity is a quantum mechanical phenomenon.
– It is characterized by the Meissner effect.
– Superconductivity cannot be understood simply as ideal conductivity in classical physics.
– Semiconductors have electrical conductivity between that of conductors and insulators.
– Current in p-type semiconductors is due to the flow of positive holes.
– Electrons in semiconductors have energy levels within certain bands.
– Semiconductors have a band gap between the valence band and the conduction band.
– The band gap determines whether a material is a semiconductor or an insulator.
Current density and Other Concepts
– Current density is the rate at which charge passes through a unit area.
– It is a vector quantity with magnitude equal to the current per unit area.
– In linear materials, current density is uniform across the conductor surface.
– Skin effect causes uneven current distribution at higher frequencies.
– Charged particles in a conductor move randomly and also drift with an average velocity.
– Electrons are the charge carriers in most metals and drift in the Source: https://en.wikipedia.org/wiki/Conventional_current
An electric current is a flow of charged particles, such as electrons or ions, moving through an electrical conductor or space. It is defined as the net rate of flow of electric charge through a surface. The moving particles are called charge carriers, which may be one of several types of particles, depending on the conductor. In electric circuits the charge carriers are often electrons moving through a wire. In semiconductors they can be electrons or holes. In an electrolyte the charge carriers are ions, while in plasma, an ionized gas, they are ions and electrons.
| Electric current | |
|---|---|
 A simple electric circuit, where current is represented by the letter i. The relationship between the voltage (V), resistance (R), and current (i or I) is V=IR; this is known as Ohm's law. | |
Common symbols | I |
| SI unit | ampere |
Derivations from other quantities | |
| Dimension | |
In the International System of Units (SI), electric current is expressed in units of ampere (sometimes called an "amp", symbol A), which is equivalent to one coulomb per second. The ampere is an SI base unit and electric current is a base quantity in the International System of Quantities (ISQ). Electric current is also known as amperage and is measured using a device called an ammeter.
Electric currents create magnetic fields, which are used in motors, generators, inductors, and transformers. In ordinary conductors, they cause Joule heating, which creates light in incandescent light bulbs. Time-varying currents emit electromagnetic waves, which are used in telecommunications to broadcast information.
