How Fast Does Electricity Travel Through Transmission Lines
What is the speed of electricity?
Category: Physics Published: February 19, 2014
Electromagnetic energy and information travel down a wire at close to the speed of light. The actual electrons travel much slower. Public Domain Prototype, source: Christopher S. Baird.
The speed of electricity really depends on what yous hateful by the word "electricity". This discussion is very full general and basically means, "all things relating to electric charge". I volition assume we are referring to a electric current of electrical accuse traveling through a metal wire, such as through the power cord of a lamp. In the case of electric currents traveling through metal wires, there are three different velocities present, all of them physically meaningful:
- The private electron velocity
- The electron drift velocity
- The point velocity
In order to understand each of these speeds and why they are all unlike and withal physically meaningful, we need to empathise the nuts of electric currents. Electric currents in metal wires are formed past gratis electrons that are moving. In the context of typical electric currents in metal wires, free electrons tin can be thought of equally little assurance bouncing effectually in the grid of fixed, heavy atoms that make up the metallic wire. Electrons are really quantum entities, but the more accurate quantum flick is non necessary in this explanation. (When y'all add in quantum effects, the individual electron velocity becomes the "Fermi velocity".) The non-gratis electrons, or valence electrons, are leap too tightly to atoms to contribute to the electric current and so can be ignored in this picture. Each costless electron in the metal wire is constantly flying in a direct line nether its ain momentum, colliding with an atom, irresolute management because of the standoff, and continuing on in a straight line again until the next collision. If a metal wire is left to itself, the free electrons inside constantly wing about and collide into atoms in a random fashion. Macroscopically, we call the random move of small particles "rut". The actual speed of an private electron is the corporeality of nanometers per second that an electron travels while going in a straight line betwixt collisions. A wire left to itself carries no electric indicate, and then the individual electron velocity of the randomly moving electrons is merely a description of the heat in the wire and not the electric electric current.
Now, if yous connect the wire to a battery, you lot have applied an external electrical field to the wire. The electric field points in 1 direction down the length of the wire. The free electrons in the wire feel a force from this electric field and speed upwards in the management of the field (in the contrary management, actually, because electrons are negatively charged). The electrons go along to collide with atoms, which nonetheless causes them to bounce all effectually in unlike directions. Merely on top of this random thermal motion, they now accept a net ordered movement in the direction opposite of the electric field. The electrical current in the wire consists of the ordered portion of the electrons' motility, whereas the random portion of the motion however but constitutes the oestrus in the wire. An applied electric field (such as from connecting a battery) therefore causes an electrical electric current to period down the wire. The boilerplate speed at which the electrons move down a wire is what we call the "drift velocity".
Even though the electrons are, on average, drifting down the wire at the migrate velocity, this does not mean that the effects of the electrons' move travels at this velocity. Electrons are not really solid balls. They exercise not interact with each other by literally knocking into each other's surfaces. Rather, electrons interact through the electromagnetic field. The closer two electrons get to each other, the stronger they repel each other through their electromagnetic fields. The interesting affair is that when an electron moves, its field moves with it, so that the electron can push some other electron farther down the wire through its field long before physically reaching the same location in space as this electron. As a event, the electromagnetic effects can travel downwards a metal wire much faster than whatsoever individual electron can. These "effects" are fluctuations in the electromagnetic field as it couples to the electrons and propagates down the wire. Since free energy and information are carried by fluctuations in the electromagnetic field, energy and information also travel much faster down an electrical wire than whatever private electron.
The speed at which electromagnetic furnishings travel down a wire is called the "signal velocity", "the wave velocity", or "the group velocity". Note that some books allude that the betoken velocity describes a purely electromagnetic wave effect. This insinuation can exist misleading. If the signal traveling down an electric cable was an isolated electromagnetic wave, then the betoken would travel at the speed of light in vacuum c. But it does not. Rather, the indicate traveling down an electric cable involves an interaction of both the electromagnetic field fluctuations (the wave) and the electrons. For this reason, the signal velocity is much faster than the electron drift velocity merely is slower than the speed of light in vacuum. By and large, the signal velocity is somewhat close to the speed of light in vacuum. Note that the "signal velocity" discussed here describes the physical speed of electromagnetic effects traveling down a wire. In contrast, engineers often use the phrase "bespeak speed" in a non-scientific way when they actually mean "scrap rate". While the bit rate of a digital signal traveling through a network does depend on the physical point velocity in the wires, information technology as well depends on how well the computers in the network tin can road the signals through the network.
Consider this analogy. A long line of people is waiting to enter a restaurant. Each person fidgets nervously well-nigh in their spot in line. The person at the end of the line grows impatient and shoves the person in forepart of him. In turn, when each person in the line receives a shove from the person behind him, he shoves the person in front end of him. The shove will therefore be passed forth from person to person, forrad through the line. The shove will accomplish the eatery doors long before the concluding person in line personally makes it to the doors. In this illustration, the people correspond the electrons, their arms represent the electromagnetic field, and the shove represents a fluctuation or wave in the electromagnetic field. The speed at which each person fidgets represents the private electron velocity, the speed at which each person individually progresses through the line represents the electron drift velocity, and the speed at which the shove travels through the line represents the signal velocity. Based on this simple analogy, we would wait the signal velocity to be very fast, the individual velocity to be somewhat fast, and the migrate velocity to be tiresome. (Note that in physics in that location is too another relevant speed in this context called the "phase velocity". The stage velocity is more of a mathematical tool than a physical reality, and so I do not think information technology is worth discussing here).
The individual electron velocity in a metal wire is typically millions of kilometers per hour. In contrast, the drift velocity is typically only a few meters per hour while the signal velocity is a hundred one thousand thousand to a trillion kilometers per hr. In full general, the signal velocity is somewhat close to the speed of light in vacuum, the individual electron speed is about 100 times slower than the signal velocity, and the electron drift speed is as boring as a snail.
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