Resistors

In simple terms, resistors do what the name suggests: they resist current. Resistors are two-terminal electrical or electronic components that resist an electric current by producing a voltage drop between its terminals in accordance with Ohm's law which states that the electrical resistance is equal to the voltage drop across the resistor divided by the current through the resistor. More on Ohm's Law is below.

It should be noted by the novice that resistors are used extensively as part of electrical networks and electronic circuits. Any study of electronics must include the study of resistors and Ohm's Law.

There are many different types of resistors. Some are more commonly used than others. In order to use resistors or to understand them one must be able to "read" them.

Most axial resistors use a pattern of colored stripes to indicate resistance. Surface-mounted resistors are marked numerically. Cases are usually brown, blue, or green, though other colors are occasionally found such as dark red or dark gray.

One can use a multimeter or ohmmeter to test the values of a resistor and it is usually a good idea to do this test if a multimeter is available.

The most common form of identification is the four band method. Four-band identification is the most commonly used color coding scheme on all resistors. It consists of four colored bands that are painted around the body of the resistor.

The color scheme is simple: The first two numbers are the first two significant digits of the resistance value, the third is a multiplier, and the fourth is the tolerance of the value. Each color corresponds to a certain number. The tolerance for a 4-band resistor will be 2%, 5%, or 10%.

In order to use this method you must have access to the color chart or you must have memorized the color chart. The Standard EIA Color Code Table per EIA-RS-279 can be found online.


Ohm's Law:

The relationship between voltage, current, and resistance through a metal wire is given by a simple equation called Ohm's Law:

I=V/R

V=Voltage; I=Current (in amperes); R=Resistance in Ohms.

When first beginning to work with resistors, you should learn the color chart so that you can correctly identify the value of the resistors. You should learn to calculate using Ohm's Law; and you should always be willing to double check your resistors with a multimeter to ensure that they are correct. Using the wrong resistor in a project can ruin the project once power is applied to the system.