Why does a wire heat up if a current passes through it?
An electric current is a stream of charged particles moving through an electrical conductor.The net rate of flow of electric charge through a surface or into a control volume is measured.The moving particles are called charge carriers, which are one of several types of particles.The charge carriers move electrons through a wire.They can be either electrons or holes.In a electrolyte, the charge carriers are ion and electron.[4]
The ampere is the flow of electric charge across a surface at a rate of one coulomb per second.A device called an ammeter is used to measure electric current.[2]:788
Magnetic fields are created by electric currents.They cause Joule heating, which creates light in light bulbs.Time-varying currents are used in telecommunications.
The French phrase intensité du courant means "current intensity" and the symbol for current is I.Current intensity is often referred to as current.The I symbol was used by Ampre in formulating his force law.At least one journal used C to I until 1896, when it became standard.[9]
Charge carriers are the moving charged particles that constitute the electric current.In metals, the positively charged atomic nuclei of the atoms are held in a fixed position, and the negatively charged electrons are free to move about in the metal.The charge carriers can be positive or negative depending on the dopant used.Positive and negative charge carriers can be present at the same time in a cell.
An equal flow of positive and negative charges has the same effect on a circuit.Since current can be either positive or negative, a convention is needed for the direction of current that is independent of charge carriers.The direction of conventional current is determined by the direction in which positive charges flow.Negatively charged carriers, such as the electrons, flow in the opposite direction of conventional current in an electrical circuit.
A current can flow in either direction.When defining a variable to represent the current, the direction of the positive current must be specified by an arrow on the schematic diagram.This is the reference direction of the current style.When analyzing electrical circuits, the direction of current through a specific circuit element is usually unknown until the analysis is complete.The reference directions of currents can be assigned in different ways.When the circuit is solved, a negative value for the current means the actual direction of current through that circuit element is opposite of the reference direction.[b]:29
The potential difference between the two points is directly proportional to the current through a conductor.The constant of proportionality is a mathematical equation that describes the relationship between it and the resistance.
V and R are the potential difference and resistance of the conductor in units of volts and ohms, respectively.According to Ohm's law, the R in this relation is constant.It was [13].
The movement of the electric charge periodically reverses direction in alternating current systems.Electric power is usually delivered to businesses and residences in AC.Some applications use triangular or square waves instead of the usual sine wave in their AC power circuits.Audio and radio signals are carried on electrical wires.Recovering information onto the AC signal is an important goal in these applications.
Direct current is a system in which the movement of electric charge in one direction.Direct current can be produced by sources such as batteries, thermocouples, solar cells, and commutator-type electric machines.A rectifier can be used to convert alternating current to direct current.Direct current can flow through a conductor such as a wire, as well as through an electron or ion beam.The old name was galvanic current.There are no comments at this time.
Natural observable examples of electrical current include lightning, static electric discharge, and the solar wind.
The overhead power lines that deliver electrical energy across long distances and the smaller wires within electrical and electronic equipment are examples of man-made occurrences of electric current.There are electric currents that occur in conductors.Electric currents occur in the surface of conductors that have been exposed to waves.Radio waves are generated when electric currents flow at the correct voltages.
In electronics, other forms of electric current include the flow of electrons through resistors or through the vacuum in a vacuum tube.
The method of measuring electric current with a galvanometer involves breaking the electrical circuit, which is inconvenient.
Current can be measured by detecting the magnetic field associated with the current.Various techniques are used to measure current.
Joule heating is the process of power dissipation by which the passage of an electric current through a conductor increases the internal energy of the conductor.fn.James Joule studied the phenomenon in the 19th century.Joule immersed a length of wire in a fixed mass of water and measured the temperature rise due to a known current through the wire.The heat produced by the wire was proportional to the square of the current and the electrical resistance of it.
Joule's Law refers to this relationship.The symbol J was given to the SI unit of energy.The watt is the SI unit of power and is equivalent to one joule per second.[4]:20
An electric current flows through a coil of wires in an electromagnet.The coil loses its magnetism when the current is turned off.A magnetic field is created by electric current.As long as there is current, the magnetic field can be visualized as a pattern of circular field lines surrounding the wire.
Electric currents can be made using magnetic fields.When a magnetic field is applied to a conductor, an electric current starts when there is a suitable path.
Radio waves can be generated when an electric current flows in a conductor.Electric currents can be caused by these travel at the speed of light.
From lower to higher electrical potential, electric charge flows by means of electrons.Any stream of charged objects may constitute an electric current in other media.Conventional current is defined as moving in the same direction as the positive charge flow.Conventional current is in the opposite direction to the electron movement in metals where the charge carriers are negative.Conventional current is in the same direction as the charge carriers when conductors are positive.
A beam of electrons may be formed in a vacuum.The electric current is caused by the flow of both positively and negatively charged particles at the same time.Positive charge flow is to blame for the current in still others.The electric currents in electrolytes can be either positively or negatively charged.The electric currents in a lead-acid cell are made up of positive and negative sulfate ion.Positive and negative ion flows are part of the electric currents in sparks.The electric current in ice and solid electrolytes is composed of flowing ionized water.
In a metal, some of the outer electrons in each atom are free to move within the metal lattice as they are in other materials.These electrons can carry a current.There are many free electrons in the lattice of metals.On average, there is zero net current within the metal with no external electric field applied.The average speed at room temperature is 106 metres per second.The electrons move in both directions across the surface when a metal wire passes through it.The metallic substances differ from all other materials by the fact that the outer shells of their atoms are bound rather loose.The metal's interior is filled with a large number of electrons that travel aimlessly around.When a metal wire is subjected to electric force applied on its opposite ends, free electrons rush in the direction of the force, forming what we call an electric current.
An electric field is created when a metal wire is connected to a battery's two terminals.The free electrons of the conductor are forced to move toward the positive terminal when contact is made.The charge carrier is the free electrons.
The current I can be calculated with the following equation.
I am in amperes if Q and t are measured in seconds and coulombs.
Electric current can be represented as the rate at which charge flows through a surface.
The electric currents in electrolytes are caused by charged particles.If an electric field is placed across a solution of Na+ and Cl and conditions are right, the sodium ion will move towards the negative electrode.The reactions take place at both surfaces.
Positive hydrogen ion are mobile and can be found in water-ice and certain solid electrolytes.The electric currents in these materials are composed of protons and not electrons.
There are moving electric charges in certain electrolyte mixtures.The current is visible due to the slow progress of the colour.[20]
In air and other ordinary gases below the breakdown field, the dominant source of electrical conduction is via relatively few mobile ion produced by radioactive gases, ultraviolet light, or Cosmic rays.Dielectric gases are those that are low in electrical conductivity.When the electric field approaches the breakdown value, free electrons become sufficiently accelerated by the field to create additional electrons by colliding, and ionizing, neutral gas atoms or Molecules.The breakdown process creates an electrical conductor that contains mobile electrons and positive ion.It forms a light emitting path in the process.
The state of matter where some of the electrons in a gas are stripped or "ionized" is called plasm.A high electric or alternating magnetic field can be used to form a plasma.Due to their lower mass, the electrons in a plasma accelerate more quickly in response to an electric field than the heavier positive ion, and hence carry the bulk of the current.The free ion recombines to create new chemical compounds when atmospheric oxygen is broken into single oxygen and ozone is created.[21]
Since there is no charged particles in a vacuum, it behaves as a perfect insulator.Free electrons or ion can be injected into the vacuum through either a field electron emission or thermionic emission.Field electron emission occurs when the electric field at the surface of the metal is high enough to cause tunneling, which results in the ejection of free electrons into the vacuum.Externally heated electrodes can be used to generate an electron cloud in vacuum tubes.When small incandescent regions are formed, thermionic emission can produce electron clouds.These regions of the surface are created by a high current.When a vacuum arcs, thermionic emission is sustained by field electron emission.The small electron-emitting regions can form quickly on a metal surface.The vacuum tubes and sprytrons are electronic devices.
Superconductivity is a phenomenon of zero electrical resistance and magnetic fields in certain materials when they are cooled.Onnes discovered it on April 8, 1911.Superconductivity is a quantum mechanical phenomenon.The complete ejection of magnetic field lines from the interior of the superconductor is called the Meissner effect.Superconductivity can't be understood simply as the idealization of perfect conductivity in classical physics.
Sometimes it's useful to think of the current as being due to the flow of positive "holes", where there is a missing electron.This is the case with a p-type Semiconductor.A conductor and an insturment have the same electrical conductivity.The range of 102 to 104 Siemens per centimeter is what this means.
electrons can only have energies within certain bandsThere are different levels of energy.The energy of the ground state, the state in which electrons are tightly bound to the atomic nucleus, and the free electron energy are where the bands are located.The energy bands correspond to many quantum states of electrons, and most of the states with low energy are occupied, up to a particular band called the valence band.The difference between metals and Semiconductors is that the metal's valence band is nearly filled with electrons under normal operating conditions, while very few (semiconductor) or virtually none (insulator) of them are available in the conduction band.
The band gap between the bands affects the ease of exciting electrons in the Semiconductor.An arbitrary dividing line is created by the size of the energy band gap.
An electron moves by hopping between bonds.Lifting the electron into the higher anti-bonding state of the bond is required by the Pauli exclusion principle.In a delocalized state, for every energy there is a state with electrons flowing in one direction and another in the other.More states for one direction than for the other must be occupied for a net current to flow.The next higher states lie above the band gap, so energy is required for this to happen.It's often said that full bands don't contribute to the electrical conductivity.As a Semiconductor's temperature rises above absolute zero, there is more energy in the Semiconductor to spend on lattice vibration and exciting electrons.The electrons in the band are called free electrons if they are clear in context.
Current density is the rate at which charge passes through a unit area.The current per unit cross-sectional area is what it is defined as.The direction is arbitrary.If the moving charges are positive, the current density has the same sign as the charges.The sign of current density is different to the speed of the charges.Current density is expressed in the base units of amperes per square metres.[4]:22
The current density across the conductor surface is uniform in linear materials.Ohm's law states that the current is proportional to the potential difference between two ends of that metal.
The current, the potential difference, and the resistance are measured in amperes.The skin effect causes the current to spread evenly across the conductor cross-section, increasing the apparent resistance.
The particles of a gas are similar to the charged particles within a conductor.More accurately, a Fermi gas.The particles must move together with an average drift rate in order to create a net flow of charge.The charge carriers in most metals follow an erratic path, bouncing from atom to atom, but generally drifting in the opposite direction of the electric field.The equation can be used to calculate the speed at which they drift.