Resistors
As the name implies the purpose of a resistor is to resist the flow of electric current. The resultant voltage that flows through the small and colorful electronic device known as resistors is equal to the value of the resistor multiplied by the current that is flowing through the resistor. This equation is an approximation that assumes that the resistor is perfect. In reality no resistors have an exact value but this approximation is considered to be acceptable for most uses. There are many different types of resistors but some of the most common are fixed value resistors, variable resistors and thermistors.Types of Resistors
The most common types of resistors included fixed value resistors, variable resistors and thermistors. A fixed value resistor is a type of resistor in which the value of the resistor in ohms does not vary. Fixed value resistors are helpful when maintaining a constant resistance value is necessary. Variable resistors, also known as potentiometers, are resistor in which the value of the resistor can be altered by turning a shaft or sliding another control. These types of resistors are often used on volume controls for audio equipment. A thermistor is a type of variable resistor where the resistance value is dependent on the temperature. There are two types of thermistors including positive temperature coefficient resistors and negative temperature coefficient resistors. In a positive temperature coefficient resistor the resistance value rises with the temperature and in a negative temperature coefficient resistor the resistance value drops when the temperature drops.
Reading Resistors
Resistors typically have brightly colored rings on them that are used to indicate the value of the resistor. Most resistors have four colored bands on them and the first two indicate the base value of the resistor, the third gives a multiplier and the fourth indicates the tolerance. To read a resistor first find the tolerance band which is usually gold or silver, then start at the other end of the resistor. The values for the various colors are as follows:
Black = 0
Brown = 1
Red = 2
Orange = 3
Yellow = 4
Green = 5
Blue = 6
Violet = 7
Gray = 8
White = 9
The simple way to determine the resistance value of a particular resistor is to write down the number associated with the first two color bands on the resistor and then add the number of zeros associated with the third color band. For example if the three colors were orange, red and yellow the resistance value would be 320,000. The fourth band represents the tolerance value and gold is equal to a 5% tolerance and silver is equal to a 10% tolerance. If there are only three bands the tolerance is equal to 20%.