Electrical Resistance© Copyright NewPath Learning. All Rights Reserved. 94-4490Visit www.newpathlearning.com for Online Learning Resources.temperatureresistancecopper wire-40-40-30-20-1001020304050-2002040608010012060708090100140160180200copper wiretemperatureresistanceElectrical ResistanceAn electrical current is affected by the resistance of the material it is flowing through. Resistance is measured in units called ohms, symbolized by the Greek letter omega (). In equations, resistance is symbolized with an R. If the voltage remains the same, increasing the resistance will result in a decrease in the current. Factors that affect resistance include an object's material, temperature, length and thickness. 1520304070OHMSD.C.OHMS10020050010543210100806040200A.C.300240180120600Ohm meterQuantityMeasurementResistanceRohmUnitSymbolUnit of MeasureFormulaAbbreviationResistance Factors - Material Materials that are good conductors have less resistance, because their electrons are held loosely on the atoms. Materials that are good insulators have a higher resistance because their electrons are held tightly together, and electrical charges have difficulty moving. Resistance = VoltageCurrent10 = 120 V12 A10 = 30 V3 Amore resistancelonger, thinner wireless resistancethicker wireOhm's LawGeorg Ohm, a Bavarian mathematician and physicist, defined the relationship between resistance, voltage and current. The formula for this relationship, known as Ohm's Law, is resistance equals voltage divided by current. For example, if the voltage of a toaster is 120 volts and the current is 12 amps, then the resistance of the toaster is 10 ohms. Resistance = VoltageCurrent10 = 120 V12 A10 = 30 V3 AResistance Factors - TemperatureSome materials will increase in resistance as the temperature increases. Copper atoms within a wire move faster as they gain thermal energy. This increased molecular movement creates resistance by slowing down the flow of electric charges through the wire.Resistance Factors - Length & ThicknessA wire's length and thickness affect resistance. Longer wires produce more resistance than shorter wires. As the electrical charges move through the length of the wire, they slow down as they collide with the walls of the wire. Thinner wires are more resistant than thicker wires. Thin wires have less area for the charges to flow through, and therefore the current is slower than thick wires.
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