RESISTANCE

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.

THEORY Notice Thus anytime as the resistance current needs to be limited in a circuit, a resistor can be added. Notice as the resistance increases the current decreases. Resistance Current

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. How can we determine the resister’s value? There are two ways - measuring with a meter or reading the color code. The schematic symbols for each type are on the right. The arrow is used to denote a resistor that is variable or controllable. Schematics Fixed Resistors Potentiometers

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

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 Number of Zeros First Number Second Number Accuracy 4 7 0 0 Ohms @ 10 % accuracy

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 Highest Lowest