What is a Resistor?


A resistor is an electronic component that resists the flow of electrons.  For example; imagine if you will, a corridor full of people trying to get through a narrow opening, all can not get through the opening at one time.  If the opening were wider more could pass through and of course if the opening was smaller, less, than at first could pass.  Resistors do the same with electrons.  Resistors are color coded to display their resistance value, the resistance value corresponds to the opening in our example. If the resistance value is high the opening is smaller (less electrons pass) and consequently if the resistance value is small the opening is larger (more electrons pass); the resistance can be so small that the opening can be nearly wide open letting nearly all pass.  Resistor color codes should be memorized, as the resistor is the most widely used component in electronics. They come in different categories and sizes. More on the different types later.  Resistors are selected by their resistance value (ohms) and current capacity (watts). Popular wattages are 1/8, 1/4, 1/2, 1, 2, 5 and 10 just to name a few. More on ohms and watts later.  Most resistors have 4 color bands. The first three from left to right give the resistance value, the last band is the tolerance value.

For example: look at the chart below, notice the color and associated number. 
The first two bands indicate the main value and the third band is the multiplier
(first band number, second band number  X 10(third band number). 
If the first band color is brown, the second is black and the third is brown, we would have
10 X 10(1) = 100 ohm resistor. If another resistor has the first three band colors of   brown, black and red, then the value would be 10 X 10(2) = 1000 ohms. 

 Black  Brown  Red  Orange  Yellow  Green  Blue  Violet  Gray  White
 0  1  2  3  4  5  6  7  8  9

Popular tolerance values range from 1% to 20%. The fourth color band represents the tolerance value. Gold for 5% tolerance, Silver for 10% tolerance and no color for 20% tolerance.  That means if your resistor has a resistance value of 100 ohms, and the fourth band represents a 10%  tolerance (silver), your 100 ohm resistor can be between 90 ohms and 110 ohms.  There can be up to 7 bands on a resistor,  three to represent the main value, a multiplier, tolerance value, quality value and % failure rate value.

The symbol for the resistor on a schematic is shown below.


There are many types of resistors: Fixed, Fixed Tapped, Miniature, Surface Mount, Potentiometer, Power, Precision, Rheostat, Sliding Tapped, Variable and last but not all Trimmer. They are made from different materials for different applications. Electronics is one of those fields that you just can't learn everything in one day and from one source.

Additional reading and experimentation can be found in, Greg S. Carpenters Book, "Introduction to Basic Electronics Hands-On Mini Course".  For more information on the book, Click Here!

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