ECEN 1400 - Introduction to Digital and Analog Electronics

Peter Mathys, Spring 2014


Resistors

The schematic symbol for a resistor is shown on the left in the figure below. Variable resistors, like the one shown on the right, are called potentiometers. CCW stands for counterclockwise and the arrow shows in which direction the slider moves when the potentimeter is turned counterclockwise.

A Resistor and a Potentiometer

Examples of real resistors are shown in the picture below (click on the picture to enlarge). Resistors convert electrical energy to thermal energy or heat. Thus, in addition to the specification of the resistance in ohms, resistors are also characterized by the maximum power (i.e., the maximum rate at which electrical energy can be converted to thermal energy) they can handle without getting damaged. The six leftmost resistors are 1/4 W resistors. The next two are 1/2 W resistors, and the last two are 4 W and 5 W resistors, respectively.

Different Examples of Resistors

To save space and increase readability, many resistors are marked using a color code rather than being labeled directly with a numerical value in ohms. Most resistors that you will use in the lab have 4 colored rings. The first two are the first two significant digits of the value, the third is a multiplier for that value, and the fourth gives the tolerance of the value. Occasionally you might see a fifth colored ring. In some cases this indicates the failure rate level of the resistor (i.e., an indication of the reliability of the resistor), in other cases 5 rings are used for high precision resistors (±1% tolerance or better) that need three significant digits to specify their value. The following table shows the meaning of the different colors in the different positions for resistors with 4 (or 5 for 1% resistors) colored rings.

Color First Digit Second Digit Third Digit
1% Resistors
Multiplier Tolerance
Black 0 0 0 1  
Brown 1 1 1 10 ±1%
Red 2 2 2 100 ±2%
Orange 3 3 3 1000 (=1k)  
Yellow 4 4 4 10k  
Green 5 5 5 100k  
Blue 6 6 6 1000k (=1M)  
Violet 7 7 7 10M  
Gray 8 8 8 100M  
White 9 9 9 1000M (=1G)  
Gold       0.1 ±5%
Silver       0.01 ±10%

Standard values in which resistors are manufactured are shown in the following table.

 Standard Resistor Values (Multiply by 0.1,1,10,100,1000,10000,100000) 
101522334768
111624365175
121827395682
132030436291

The most commonly used values are shown in bold in the first line and the least often used values are shown in the fields shaded in gray. By using the multipliers, several ranges of magnitude are covered, e.g., the value 22 in the table leads to standard resistor values of

2.2, 22, 220, 2.2k, 22k, 220k, 2.2M

The most common tolerances for 1/8, 1/4, and 1/2 W resistors are 5% and 1%.