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## RESISTANCE

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**DEFINED**- Opposition to electron flow. - The resistance in a metal conductor is directly proportional to the length and inversely proportional to the cross-sectional area. R=Resistance р=specific resistance l=length A=Cross-Sectional Area**DEFINED**- Increase in temperature will also increase resistance. -Resistance is measured in Ohms (Ω) -Resistance sounds like a bad thing but we tend to use it to our advantage in most circuits.**Current**Current Resistance THEORY Thus anytime current needs to be limited in a circuit, a resistor can be added. Notice as the resistance increases the current decreases.**Schematics**Fixed Resistors Potentiometers RESISTORS Resistors are devices that turn electrical current into heat energy. This is valuable to limit current flow to another portion of a circuit. There are two main types of resistors, fixed and variable. The variable resistor may also be called a potentiometer. The schematic symbols for each type are on the right. The arrow is used to denote a resistor that is variable or controllable. How can we determine the resister’s value? There are two ways - measuring with a meter or reading the color code.**Resistance Color Code**First Number Second Number Tolerance /Accuracy Fixed resistors use color bands to make it easy to read their resistance from any angle or position Number of Zeros or if: Gold - divide by 10 Silver - divide by 100**Number of Zeros**Accuracy Second Number First Number Black = 0 Brown = 1 Red = 2 Orange =3 Yellow = 4 Green =5 Blue = 6 Violet = 7 Gray = 8 White = 9 Third color band: gold= divide by 10 silver = divide by 100 Fourth color band: gold = 5 % = .05 silver = 10 % = .10 4 7 0 0 Ohms @ 10 %accuracy**Highest**Lowest Black = 0 Brown = 1 Red = 2 Orange =3 Yellow = 4 Green =5 Blue = 6 Violet = 7 Gray = 8 White = 9 Third color band: gold= divide by 10 silver = divide by 100 Fourth color band: gold = 5 % = .05 silver = 10 % = .10 Use the accuracy band to determine the resistors acceptable range of resistance 5 6 0 0 0 @ 10 % 5 6 0 0 0 Acceptable Range .10 5 6 0 0 0 5 6 0 0 0 5 6 0 0.0 0 + 5 6 0 0 - 5 6 0 0 6 1 6 0 0 5 0 4 0 0