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Resistors

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Resistors Theory

A resistor is a component that opposes or impedes the flow of electrons through it. Thus, it limits the current flow in a circuit. A resistor can also be used to reduce the voltage. All resistors have two basic ratings, their electrical value, expressed in ohms, and their power rating, expressed in watts. The wattage rating of a resistor is a measure of how much power it can handle without being damaged by heat and it has no bearing on the resistance value. The electrical value of a resistor is a measure of its voltage drop divided by the current flowing through it (R = E/I). There are many kinds of resistors and they appear in any mumber of shapes and sizes. Three examples of the most common types of fixed carbon resistors are shown in the figure below.

Fixed Carbon Resistors Types

A. Axial Leads	B. Radial Lead Dot	C. Radial Lead Band

The most widely used method of resistor identification is designating the value by means of a color code.

Resistor Color Code Table

Color	Color	Digits	Multiplier	Tolerance
	Black	0	1
	Brown	1	10
	Red	2	100
	Orange	3	1,000
	Yellow	4	10,000
	Green	5	100,000
	Blue	6	1,000,000
	Violet	7	10,000,000
	Gray	8	100,000,000
	White	9	1,000,000,000
	Gold		0.1	5%
	Silver		0.01	10%
	No color			20%

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