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Topic: Electrical resistance

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	Electrical resistance - Wikipedia, the free encyclopedia
		Electrical resistance is a measure of the degree to which an object opposes the passage of an electric current.
		The SI unit of electrical resistance is the ohm.
		R is the resistance of the object, usually measured in ohms.
	en.wikipedia.org /wiki/Electrical_resistance (1185 words)

	Electrical resistance - Biocrawler (Site not responding. Last check: 2007-10-22)
		Electrical resistance is a measure of the degree to which a body opposes the passage of an electric current.
		When an electrical potential (a voltage) is applied across the metal, the electrons drift from one end of the conductor to the other under the influence of the electric field.
		The electric resistance of a typical semiconductor decreases exponentially with the temperature:
	www.biocrawler.com /encyclopedia/Electrical_resistance (913 words)

	Resistance and Resistivity
		The electrical resistance of a circuit component or device is defined as the ratio of the voltage applied to the electric current whichflows through it:
		The electrical resistance of a wire would be expected to be greater for a longer wire, less for a wire of larger cross sectional area, and would be expected to depend upon the material out of which the wire is made.
		The electrical resistance of a wire would be expected to be greater for a longer wire, less for a wire of larger cross sectional area, and would be expected to depend upon the material out of which the wire is made (resistivity).
	hyperphysics.phy-astr.gsu.edu /hbase/electric/resis.html (422 words)

	Negative resistance - Wikipedia, the free encyclopedia
		Negative resistance or Negative differential resistance is a property of electrical circuit elements composed of certain materials in which, over certain voltage ranges, current is a decreasing function of the voltage.
		In electrical circuits, static resistance is the ratio of the voltage across a circuit element to the current through it.
		In compliance with the law of conservation of energy, a plot of the negative differential resistance region of a passive component cannot pass through the origin.
	en.wikipedia.org /wiki/Negative_resistance (681 words)

	Electrical Resistance in Series (Site not responding. Last check: 2007-10-22)
		Electrical resistance in a wire is a measure of the opposition to the flow of charge, electrons, or current.
		Electrical resistance occures because electrons moving through a wire bump into metal atoms and lose some of their energy as heat.
		An electrical circuit with a 6 V battery operates a floodlight that has 3 A of current flowing through it.
	webpages.charter.net /griche/pt/u4s3sprb.htm (521 words)

	Electrical resistance - (Site not responding. Last check: 2007-10-22)
		Image:Register.jpg Electrical resistance is a measure of the degree to which an object opposes the passage of an electric current.
		Resistance is the property of any object or substance of resisting or opposing the flow of an electrical current.
		The electric resistance of a typical intrinsic (non doped) semiconductor decreasesexponentially with the temperature:
	psychcentral.com /psypsych/Electrical_resistance (1229 words)

	Electrical Machinery
		Electricity is the medium that carries power from the prime mover, whether at a central power station or on the locomotive, to its point of application at the rail, and allows it to be controlled conveniently.
		Electrical motors were invented early, in the 1830's, as soon as the magnetic effects of electrical currents and the magnetic properties of iron became known.
		Electrical power generated by an alternator, or supplied by a contact wire, is first converted to direct current, then to variable-frequency three-phase for supplying induction traction motors in a locomotive.
	www.du.edu /~jcalvert/tech/elmotors.htm (6995 words)

	PFD: ELECTRICAL FIRES
		The amount of electrical power needed to make an appliance operate is called "wattage" and is a function of the amount of current flowing through the wire (amperage), and the pressure in the system (voltage).
		This is known as "ohms." Resistance causes increased heat in the wire.
		Electrical resistance also is affected by the length of a wire.
	www.ci.phoenix.az.us /FIRE/elecfire.html (1419 words)

	Essay or Coursework : Electrical resistance
		Electrical resistance is the slowing of a current through an electrical circuit.
		Resistant, is a property of any object or substance of resisting or opposing the flow of an electrical current.
		As a conductor conducts electricity as current, a resistor is the opposite.
	www.coursework.info /i/7565.html (295 words)

	thermal resistance: an oxymoron? - Article2.htm May, 1997 (Site not responding. Last check: 2007-10-22)
		Most people are of the opinion that the definition should have a physical significance, on the grounds that an electrical resistance certainly has a physical meaning (the voltage between two points divided by the current from one point to the other), and smart professors told them that electrical and thermal differential equations are identical.
		In practical circumstances, this resistance cannot be an invariant quantity designated by one number, because the orientation of internal conduction heat flow paths changes in response to changes in the thermal environment.
		However, in doing so, the resulting 'thermal resistances' lose their physical meaning completely, as argued in Ref. 4, and one may wonder if the term 'thermal resistance' should be kept, on account of the persistence of the analogy in the minds of most scientists and designers for some time to come.
	www.electronics-cooling.com /Resources/EC_Articles/MAY97/article2.htm (1537 words)

	Define resistance - a definition from Whatis.com
		Resistance is the opposition that a substance offers to the flow of electric current.
		When an electric current of one ampere passes through a component across which a potential difference (voltage) of one volt exists, then the resistance of that component is one ohm.
		The electrical resistance per unit length, area, or volume of a substance is known as resistivity.
	whatis.techtarget.com /definition/0,,sid9_gci212894,00.html (277 words)

	Electrical measurements II
		Resistance can also be measured if the current through a component is known and the voltage drop across the component measured.
		This device includes electrical networks involving a variable resistance that, when balance is achieved, allows no current to flow through the device.
		Alternating current, the type of electrical energy obtained from household wall outlets, has voltage varying as a function of time in a sinusoidal manner, a sine wave that reverses direction 120 times/second (60 full cycles per second - a 60-hertz electrical signal).
	www.eeescience.utoledo.edu /Faculty/Stierman/EEG/notes/Elec1.htm (568 words)

	Current and resistance
		Resistance in wires produces a loss of energy (usually in the form of heat), so materials with no resistance produce no energy loss when currents pass through them.
		In this case the equivalent resistance of N identical resistors is the resistance of one resistor divided by N, the number of resistors.
		Generally, the total resistance in a circuit like this is found by reducing the different series and parallel combinations step-by-step to end up with a single equivalent resistance for the circuit.
	physics.bu.edu /~duffy/PY106/Resistance.html (1871 words)

	Electrical Resistance 9-12
		The amount of electrical current that flows in a circuit depends on the resistance that the conductor offers to the flow of charge.
		A conductor with a high resistance is sometimes called a resistor and its presence in an electrical circuit can be represented using different symbols, as shown in the figures.
		The electrical resistance of a wire or any other object depends on the material the object is made of, and also on the thickness and the length of the object.
	www.chem.arizona.edu /tpp/chemt/CTSTC/CTSTCcondins9-12.htm (151 words)

	Electrical Resistance
		Find the electrical resistance of a light bulb which passes 2A of current when a potential difference of 120V is placed across it.
		A diode shows very low resistance to current flowing in one direction and very high resistance to current flowing in the opposite direction.
		Transistors are useful because their resistance to current flowing between two of their terminals depends on the current which flows in a third, control terminal.
	www.people.vcu.edu /~rgowdy/mod/086/xmp.htm (162 words)

	Essay or Coursework : An Investigation into the factors that affect the electrical resistance of a wire
		Coursework and Essays: By Level: GCSE: Physics: Resistance: Resistance of a Wire: An Investigation into the factors that affect the electrical resistance of a wir
		An electrical conductor is a substance through which electrical current flows with little resistance.
		Electricity is passed through a conductor, in this case a length of wire, by means of free electrons.
	www.coursework.info /i/6542.html (346 words)

	Scientists find that electrical resistance between nanotubes, graphite is tunable
		CHAPEL HILL — Electrical resistance between nanotubes -- carbon tubes so thin it would take several million lying side by side to cover an inch -- and graphite surfaces that support them varies according to how the tubes are oriented, a new University of North Carolina at Chapel Hill study shows.
		The discovery, which could be important to telecommunications and other electronics industries, indicates it’s possible to alter the resistance by changing the tubes’ position on a flat surface.
		Resistance peaks six times as the end of a nanotube is rotated 360 degrees, the scientists found.
	www.unc.edu /news/archives/nov00/superfine113000.htm (846 words)

	Basic Electrical Defintions
		Demand Factor - For an electrical system or feeder circuit, this is a ratio of the amount of connected load (in kva or amperes) that will be operating at the same time to the total amount of connected load on the circuit.
		If the value of resistance to be measured can be estimated within reasonable limits, a range selected that will give approximately half-scale deflection when the resistance is inserted between the probes.
		In all electrical systems, the conductors should be sized so that the voltage drop never exceeds 3% for power, heating, and lighting loads or combinations of these.
	www.elec-toolbox.com /basicdef.htm (2172 words)

	Build an Electrical Logging Tool
		While an oil well is being drilled, a logging tool may be lowered into the borehole to gather data that is then used to produce a kind of graph known as a log.
		An early electrical log is shown in the Science Lab experiment The Electrical Resistivity of Materials.
		We continued lowering the tool 1 cm at a time and recording resistance until the sensors were 10 cm deep.
	www.seed.slb.com /en/scictr/lab/logging (373 words)

	Electrical Resistance
		------------------------------------------------ Resistance is proportional to length and inversely proportional to cross-sectional area.
		Another way to work the problem is to imagine two identical wires of resistance R laid (1) side by side.
		The total resistance is R/2 (2) end to end.
	www.newton.dep.anl.gov /newton/askasci/1993/physics/PHY106.HTM (76 words)

	Electrical Conductivity
		Electrical conductivity (EC) estimates the amount of total dissolved salts (TDS), or the total amount of dissolved ions in the water.
		the resistance of the water, the lower its conductivity.
		Since the electrical current flow (I) increases with increasing temperature, the EC values are automatically corrected to a standard value of 25°C and the values are then technically referred to as specific electrical conductivity.
	lakeaccess.org /russ/conductivity.htm (1190 words)

	Direct Current (DC) Electrical Circuits - Succeed in Physical Science (Site not responding. Last check: 2007-10-22)
		The resistance or electrical friction is measured in Ohms.
		In an electrical circuit, several electrical devices such as light bulbs can be placed in a line or in series in the circuit between the positive and negative poles of the battery.
		Every device in a DC circuit--whether a light bulb or electrical motor--can be represented by an electrical resistance or resistor Usually, when drawing a circuit diagram or schematic, you use certain symbols for the battery and resistors.
	www.school-for-champions.com /science/dccircuits.htm (1071 words)

	electrical resistance corrosion probes
		Electrical Resistance (ER) probes utilize the relatively simple principle of an increase in electrical resistance produced by a decrease in the section thickness of a metallic conductor.
		The increase in electrical resistance of a corroding sensor is measured relative to that of a corresponding shielded reference sensor element.
		The uncorroded reference element also serves to compensate for the effects of temperature changes on resistance.
	www.corrosion-club.com /ER.htm (340 words)

	Review: Electrical Resistance (Site not responding. Last check: 2007-10-22)
		A current of 4.15 A has 625.13 ohms of resistance.
		Calculate the resistance (in ohms) of a 2.52 meter long piece of copper wire which has a diameter of 0.37 centimeters.
		What is the length of a piece of aluminum wire, if it has a resistance of 345.67-ohms and a diameter of 0.045 centimeters?
	jersey.uoregon.edu /~mstrick/Technology/Electrical/Review4_3ERes.html (185 words)

	Electrical Circuits in Parallel (Site not responding. Last check: 2007-10-22)
		Find the total resistance in the circuit by using Ohm's Law and the total voltage and total current.
		Find the total resistance by calculating it with the parallel circuit resistance equation.
		What is the total resistance across two resistors in parallel if their values are 4
	webpages.charter.net /griche/pt/u4s3pprb.htm (308 words)

	Lesson Exchange: Heat and electrical resistance (Middle, Science)
		Can be used in an electrical thematic unit or when studying heat and thermal energy.
		The lab activity should follow a discussion of heat or electrical resistance.
		Caution: very thin wire can generate enough heat to make touching the wire to the battery poles uncomfortable - students may need a strip of electrical tape to use as an insulator.
	www.teachers.net /lessons/posts/362.html (187 words)

	Electrical Resistance (Site not responding. Last check: 2007-10-22)
		Hook the ohmmeter to the contacts on the base of the ceramic light socket.
		Gently heat the glass bead while recording the resistance.
		Record the resistance and time at 10 second intervals (if possible).
	matse1.mse.uiuc.edu /~tw/ceramics/d.html (96 words)

	The Electrical Resistance (ResearchIndex) (Site not responding. Last check: 2007-10-22)
		We extend known relations between random walks and electrical networks by showing that resistance in this network is intimately connected with the lengths of random walks on the graph.
		For example, the commute time between two vertices s and t (the expected length of a random walk from s to t and back) is precisely characterized by the effective resistance R st between s and t: commute time =...
		1.8: The Electrical Resistance Of A Graph Captures Its..
	citeseer.ist.psu.edu /664467.html (219 words)

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