Electrical Resistance © Copyright NewPath Learning. All Rights Reserved. 94-4490 Visit www.newpathlearning.com for Online Learning Resources. temperature resistance copper wire -40 -40 -30 -20 -10 0 10 20 30 40 50 -20 0 20 40 60 80 100 120 60 70 80 90 100 140 160 180 200 copper wire temperature resistance Electrical Resistance An 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 (Ω). In equations, r esistance 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. 15 20 30 40 70 OHM S D. C. OHM S 100 20 0 50 0 10 5 4 3 2 1 0 100 80 60 40 20 0 A.C . 300 240 180 120 60 0 Ohm meter Quantity Measurement Resistance R ohm Unit Symbol Unit of Measure Formula Abbreviation Resistance 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 = Voltage Current 10 = 120 V 12 A 10 = 30 V 3 A more resistance longer, thinner wire less resistance thicker wire Ohm’s Law Georg 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 = Voltage Current 10 = 120 V 12 A 10 = 30 V 3 A Resistance Factors - Temperature Some 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 & Thickness A 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.
Pause and Review Use the formula to fill in the missing information below. Show your work. © Copyright NewPath Learning. All Rights Reserved. 94-4490 Visit www.newpathlearning.com for Online Learning Resources. Electrical Resistance Resistance = Voltage Current 10 = 120 V 12 A 10 = 30 V 3 A 220 Volts 11 Ω amps Current : 15 20 30 40 70 OHM S D. C. OHM S 100 20 0 50 0 10 5 4 3 2 1 0 100 80 60 40 20 0 A.C . 300 240 180 120 60 0 Ohm meter Quantity Measurement Resistance R ohm Unit Symbol Unit of Measure Formula Abbreviation 5 amps 20 Ω V Voltage : 180 Volts 9 amps Resistance : Ω
