In physics and electrical engineering , a conductor is an object or type of material that allows the flow of charge ( electric current ) in one or more directions. Materials made of metal are common electrical conductors. The flow of negatively charged electrons generates electric current, positively charged holes , and positive or negative ions in some cases.
31-409: QTC may refer to: Quantum Tunneling Composite QTc , a time measurement of a portion of a heartbeat Queensland Theological College Queensland Turf Club Quinnipiac tribal council The radio Q code for a pending message count Topics referred to by the same term [REDACTED] This disambiguation page lists articles associated with
62-400: A closed electrical circuit , one charged particle does not need to travel from the component producing the current (the current source ) to those consuming it (the loads ). Instead, the charged particle simply needs to nudge its neighbor a finite amount, who will nudge its neighbor, and on and on until a particle is nudged into the consumer, thus powering it. Essentially what is occurring is
93-454: A conductor of uniform cross section, therefore, can be computed as where ℓ {\displaystyle \ell } is the length of the conductor, measured in metres [m], A is the cross-section area of the conductor measured in square metres [m ], σ ( sigma ) is the electrical conductivity measured in siemens per meter (S·m ), and ρ ( rho ) is the electrical resistivity (also called specific electrical resistance ) of
124-418: A few hundred amperes. Aside from the geometry of the wire, temperature also has a significant effect on the efficacy of conductors. Temperature affects conductors in two main ways, the first is that materials may expand under the application of heat. The amount that the material will expand is governed by the thermal expansion coefficient specific to the material. Such an expansion (or contraction) will change
155-411: A given material, the resistance is inversely proportional to the cross-sectional area. For example, a thick copper wire has lower resistance than an otherwise-identical thin copper wire. Also, for a given material, the resistance is proportional to the length; for example, a long copper wire has higher resistance than an otherwise-identical short copper wire. The resistance R and conductance G of
186-419: A high concentration of electrons flow from one spike tip to the next. The electric current stops when the force is taken away. QTCs come in different forms and each form is used differently but has a similar resistance change when deformed. QTC pills are the most commonly used type of QTC. Pills are pressure sensitive variable resistors. The amount of electric current passed is exponentially proportionate to
217-461: A long chain of momentum transfer between mobile charge carriers ; the Drude model of conduction describes this process more rigorously. This momentum transfer model makes metal an ideal choice for a conductor; metals, characteristically, possess a delocalized sea of electrons which gives the electrons enough mobility to collide and thus affect a momentum transfer. As discussed above, electrons are
248-417: A reducing atmosphere, then oxygen-free high conductivity copper (CW008A or ASTM designation C10100) may be used. Because of its ease of connection by soldering or clamping, copper is still the most common choice for most light-gauge wires. Silver is 6% more conductive than copper, but due to cost it is not practical in most cases. However, it is used in specialized equipment, such as satellites , and as
279-585: A thin plating to mitigate skin effect losses at high frequencies. Famously, 14,700 short tons (13,300 t) of silver on loan from the United States Treasury were used in the making of the calutron magnets during World War II due to wartime shortages of copper. Aluminum wire is the most common metal in electric power transmission and distribution . Although only 61% of the conductivity of copper by cross-sectional area, its lower density makes it twice as conductive by mass. As aluminum
310-404: Is not exact: It assumes the current density is totally uniform in the conductor, which is not always true in practical situation. However, this formula still provides a good approximation for long thin conductors such as wires. Another situation this formula is not exact for is with alternating current (AC), because the skin effect inhibits current flow near the center of the conductor. Then,
341-404: Is passed through it. Liquids made of compounds with only covalent bonds cannot conduct electricity. Certain organic ionic liquids , by contrast, can conduct an electric current. While pure water is not an electrical conductor, even a small portion of ionic impurities, such as salt , can rapidly transform it into a conductor. Wires are measured by their cross sectional area. In many countries,
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#1732786979954372-477: Is restricted use of QTC due to its high cost, but eventually this technology is expected to become available to the general user. Quantum tunneling composites are combinations of polymer composites with elastic, rubber-like properties elastomer , and metal particles (nickel). Due to a no-air gap in the sensor contamination or interference between the contact points is impossible. There is also little to no chance of arcing , electrical sparks between contact points. In
403-650: Is roughly one-third the cost of copper by weight, the economic advantages are considerable when large conductors are required. The disadvantages of aluminum wiring lie in its mechanical and chemical properties. It readily forms an insulating oxide, making connections heat up. Its larger coefficient of thermal expansion than the brass materials used for connectors causes connections to loosen. Aluminum can also "creep", slowly deforming under load, which also loosens connections. These effects can be mitigated with suitably designed connectors and extra care in installation, but they have made aluminum building wiring unpopular past
434-589: Is the international standard to which all other electrical conductors are compared; the International Annealed Copper Standard conductivity is 58 MS/m , although ultra-pure copper can slightly exceed 101% IACS. The main grade of copper used for electrical applications, such as building wire, motor windings, cables and busbars , is electrolytic-tough pitch (ETP) copper (CW004A or ASTM designation C100140). If high conductivity copper must be welded or brazed or used in
465-404: Is usually insulated with PVC insulation that is only rated to operate to about 60 °C, therefore, the current in such wires must be limited so that it never heats the copper conductor above 60 °C, causing a risk of fire . Other, more expensive insulation such as Teflon or fiberglass may allow operation at much higher temperatures. If an electric field is applied to a material, and
496-484: The geometrical cross-section is different from the effective cross-section in which current actually flows, so the resistance is higher than expected. Similarly, if two conductors are near each other carrying AC current, their resistances increase due to the proximity effect . At commercial power frequency , these effects are significant for large conductors carrying large currents, such as busbars in an electrical substation , or large power cables carrying more than
527-440: The service drop . Organic compounds such as octane, which has 8 carbon atoms and 18 hydrogen atoms, cannot conduct electricity. Oils are hydrocarbons, since carbon has the property of tetracovalency and forms covalent bonds with other elements such as hydrogen, since it does not lose or gain electrons, thus does not form ions. Covalent bonds are simply the sharing of electrons. Hence, there is no separation of ions when electricity
558-455: The QTC's inactive state, the conductive elements are too far from one another to pass electron charges. Thus, current does not flow when there is no pressure on the quantum-tunneling composite. A characterization of a QTC is its spiky silicon covered surface. The spikes do not actually touch, but when a force is applied to the QTC, the spikes move closer to each other and a [quantum] effect occurs as
589-403: The amount of pressure applied. QTC pills can be used as input sensors which respond to an applied force. These pills can also be used in devices to control higher currents than QTC sheets. QTC sheets are composed of three layers: a thin layer of QTC material, a conductive material and a plastic insulator. QTC sheets allow a quick switch from high to low resistance and vice versa. In February 2008
620-438: The composite resistance grows for an incremental applied stress or force. QTCs were discovered in 1996 by technician David Lussey while he was searching for a way to develop an electrically conductive adhesive . Lussey founded Peratech Ltd, a company devoted to research work and usage of QTCs. Peratech Ltd. and other companies are working on developing quantum tunneling composite to improve touch technology. Currently, there
651-421: The conductive elements are too far apart to conduct electricity ; when pressure is applied, they move closer and electrons can tunnel through the insulator . The effect is far more pronounced than would be expected from classical (non- quantum ) effects alone, as classical electrical resistance is linear (proportional to distance), while quantum tunnelling is exponential with decreasing distance, allowing
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#1732786979954682-462: The conductor is made from (as described above) and the conductor's size. For a given material, conductors with a larger cross-sectional area have less resistance than conductors with a smaller cross-sectional area. For bare conductors, the ultimate limit is the point at which power lost to resistance causes the conductor to melt. Aside from fuses , most conductors in the real world are operated far below this limit, however. For example, household wiring
713-426: The geometry of the conductor and therefore its characteristic resistance. However, this effect is generally small, on the order of 10 . An increase in temperature will also increase the number of phonons generated within the material. A phonon is essentially a lattice vibration, or rather a small, harmonic kinetic movement of the atoms of the material. Much like the shaking of a pinball machine, phonons serve to disrupt
744-443: The material, measured in ohm-metres (Ω·m). The resistivity and conductivity are proportionality constants, and therefore depend only on the material the wire is made of, not the geometry of the wire. Resistivity and conductivity are reciprocals : ρ = 1 / σ {\displaystyle \rho =1/\sigma } . Resistivity is a measure of the material's ability to oppose electric current. This formula
775-490: The newly formed company QIO Systems Inc gained, in a deal with Peratech, the worldwide exclusive license to the intellectual property and design rights for the electronics and textile touchpads based on QTC technology and for the manufacture and sale of ElekTex (QTC-based) textile touchpads for use in both consumer and commercial applications. QTCs were used to provide fingertip sensitivity in NASA 's Robonaut in 2012. Robonaut
806-427: The path of electrons, causing them to scatter. This electron scattering will decrease the number of electron collisions and therefore will decrease the total amount of current transferred. Conduction materials include metals , electrolytes , superconductors , semiconductors , plasmas and some nonmetallic conductors such as graphite and conductive polymers . Copper has a high conductivity . Annealed copper
837-425: The primary mover in metals; however, other devices such as the cationic electrolyte (s) of a battery , or the mobile protons of the proton conductor of a fuel cell rely on positive charge carriers. Insulators are non-conducting materials with few mobile charges that support only insignificant electric currents. The resistance of a given conductor depends on the material it is made of, and on its dimensions. For
868-415: The resistance to change by a factor of up to 10 between pressured and unpressured states. Quantum tunneling composites hold multiple designations in specialized literature, such as: conductive/semi-conductive polymer composite, piezo-resistive sensor and force-sensing resistor (FSR). However, in some cases Force-sensing resistors may operate predominantly under percolation regime; this implies that
899-408: The size is expressed in square millimetres. In North America, conductors are measured by American wire gauge for smaller ones, and circular mils for larger ones. The ampacity of a conductor, that is, the amount of current it can carry, is related to its electrical resistance: a lower-resistance conductor can carry a larger value of current. The resistance, in turn, is determined by the material
930-653: The title QTC . If an internal link led you here, you may wish to change the link to point directly to the intended article. Retrieved from " https://en.wikipedia.org/w/index.php?title=QTC&oldid=745084182 " Category : Disambiguation pages Hidden categories: Short description is different from Wikidata All article disambiguation pages All disambiguation pages Quantum Tunneling Composite Quantum tunnelling composites ( QTCs ) are composite materials of metals and non- conducting elastomeric binder, used as pressure sensors . They use quantum tunnelling : without pressure ,
961-758: Was able to survive and send detailed feedback from space. The sensors on the human-like robot were able to tell how hard and where it was gripping something. Quantum tunneling composites are relatively new and are still being researched and developed. QTC has been implemented within clothing to make “smart”, touchable membrane control panels to control electronic devices within clothing, e.g. mp3 players or mobile phones. This allows equipment to be operated without removing clothing layers or opening fastenings and makes standard equipment usable in extreme weather or environmental conditions such as Arctic/Antarctic exploration or spacesuits. The following are possible uses of QTCs: Conductive In order for current to flow within