Introduction to Electronics:

Section One: Resistors

James Noll - Instructor

Resistors

Resistors are defined as: “A device used in electrical circuits to maintain a constant relation between current flow and voltage.”

Resistors are used to step up or lower the voltage at different points in a circuit and to transform a current signal into a voltage signal or vice versa, among other uses. The electrical behavior of a resistor obeys Ohm's law for a constant resistance

Resistors

The unit of measurement of a resistor is the “ohm” Resistors are made of several types of materials

including carbon, metal film and wire. Each material gives each type of resistor a certain “characteristic”.

For instance, carbon is a common resistor material used for general purpose resistors. Metal Film is a material that is used for precision resistors and is more delicate than carbon. Wire is used for high power, high current applications and is considered heavy duty.

Resistors

Resistors are generally a “two-lead” device Each resistor type has a “tolerance” or percentage

accuracy – 1%, 5%, 10%, 20%, etc. Some resistors are color coded while others have

printed information on them. The color code will be explained later.

Resistors are considered a passive device and are a fixed value.

Potentiometers are a variable resistor.

Resistors

Resistors

Resistors have a wide range of values:

Resistors range in value from less than 1 ohm to over one million ohms.

Each resistor has a “suffix” to indicate it's value For resistors less than one thousand, there is no

suffix. For resistors greater than one thousand, the suffix

is “K” For resistors greater than one million, the suffix is

“M”

Resistance Formulas

The basic formula for resistance is: R=E/I where R is resistance, E is

voltage and I is current. The formula is used in Direct

Current circuits only.