Resistor values
In theory, a resistor can have any value from the lowest possible (such as a shaft of solid silver) to the highest (open air). In practice, it is unusual to find resistors with values less than about 0.1 Ω, or more than about 100 MΩ.
Resistors are manufactured in standard values that might at first seem rather odd to you. The standard numbers are 1.0, 1.2, 1.5,1.8, 2.2, 2.7, 3.3, 3.9, 4.7, 5.6, 6.8, and 8.2. Units are commonly made with values derived from these values, multiplied by some power of 10. Thus, you will see units of 47 Ω, 180 Ω, 6.8 KΩ, or 18 MΩ, but not 380 Ω or 650 KΩ. Maybe you’ve wondered at some of the resistor values that have been used in problems and quiz questions in previous chapters. Now you know that these choices weren’t totally arbitrary; they were picked to represent values you might find in real circuits.
In addition to the above values, there are others that are used for resistors made with greater precision, or tighter tolerance. These are power-of-10 multiples of 1.1, 1.3, 1. 6, 2.0, 2.4, 3.0, 3.6, 4.3, 5.1, 6.2, 7.5, and 9.1.
You don’t have to memorize these numbers. They’ll become familiar enough over time, as you work with electrical and electronic circuits.
