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What is DC Electricity. Chapter 2 Resistance The property of a material to inhibit the flow of current. Resistor Resistor Molded Carbon Composite Resistor Film Molded Carbon Composite Wirewound Wire wound Film Surface Mount Technology SMT Resistivity A Resistivity: Example A 1m long piece of gold has a cross 2 sectional area of 0.1cm . The resistivity of gold at 20°C is 2.24 X 10-8 ohm-meters.ρ -8 10 ρ =2.24 X 2 A = 0.1cm L = 1m ohm-meters L = 1m Resistivity: Gold ρ =2.24 X 10-8 ohm-meters 2 L = 1m A = 0.1cm ρL R= A R= (2.24 X 10-8 Ώ-m)(1m) 2 0.00001m R =0.00224 Ώ Resistivity: Carbon ρ =50 X 10-5 ohm-meters 2 L = 1m A = 0.1cm ρL R= A R= (50 X 10-5 Ώ-m)(1m) R =50 Ώ 2 0.00001m Resistor Color Code 0 1 2 3 4 5 6 7 8 9 Tolerance The measure of how good a component is. How close it is to the actual value. 5% 10% 20% Gold Silver No Band Tolerance 5%: 95-105Ω 100Ω 10%: 90-110Ω 20%: 80-120Ω } Digits 36 Multiplier 00000 Tolerance 5% R =3600000 Ώ or 3.6M Ώ } Digits 47 Multiplier R =36 Ώ Tolerance 20 % Voltage Sources Voltage sources added in Series increase the Voltage and the Current stays the same. V = 1.5v I = 1A V = 4.5v I = 1A Voltage Sources Voltage sources added in Parallel increase the Current and the Voltage stays the same. V = 1.5v I = 1A V = 1.5v I = 3A Battery: V = 1.5v, I = 1A V=3v I=1A I=1A I=1A Exampl e V=3v I= 3A Ohm’s Law The Current(I) in a circuit is directly proportional to the Voltage(E,V) and inversely proportional to the Resistance(R). E I= R Ohm’s Law E I R Find: E E= x IR Ohm’s Law E I R Find: R R = E/I Ohm’s Law E I R Find: I I = E/R Ohm’s Law Units Ev IA RΩ Ohm’s Law Units E(v) ImA RkΩ Ohm’s Law Units E(v) IμA RMΩ Ohm’s Law Example Ev IA RΩ R=2Ω, E=12v Find: I I = E/R =12v/2Ω I = 6A Ohm’s Law Example Ev E=120, I=60mA Find: R R = E/I ImA RkΩ =120v/60mA R = 2kΩ Ohm’s Law Example Ev R=10kΩ, I=12mA Find: E E = IxR ImA RkΩ =12mAx10kΩ I = 120v Wheel of Answers Ev IA RΩ Ev ImA RkΩ