INTRODUCTION TO ELECTRONICS: Electrical Units and Metric Prefixes

Physical realities would be meaningless without internationally standardized definitions that quantify their existence. Within the field of electronics, there are electrical units of measure that are so common that becoming familiar with them is highly advisable for new students. It is important to note that the aforementioned electrical phenomena occur in measured quantities that are very large and small alike. This necessitates the usage of power-of-ten metric prefixes in conjunction with SI Unit definitions. Let’s first consider one of the most common expressions of voltage:

V = IR

The usage of symbols ( alphabetical or otherwise ) to represent electrical units of measure greatly simplifies the problem-solving process. Mathematical operations are first carried out with symbols whose values are later substituted with the appropriate SI unit values. For example, let’s assume the following quantities of current ( I ) and resistance ( R ) are used to determine a value for voltage ( V ). Each equation consists of a symbol that is related to an SI value of our choosing:

I = 1,000 amperes ( A ) = 1,000A

R = 1/1,000 ohm = 1/1,000 Ω

Imagine how tedious it would be to use the SI values in a multi-step problem. By using symbols first, we can manipulate the basic equation with relative ease prior to SI unit substitution. We are now ready to substitute our Sl unit values into the equation:

V = IR

V = ( 1,000 A )( 1/1,000 Ω ) = 1V

Appropriate substitution has been carried out, but the equation is still somewhat cumbersome. It would have been easier to use power-of-ten metric prefixes along with the SI units in question:

1,000 = 10³ = 1 kilo = 1k

( 1/1,000 ) = 10^-3 = 1 milli = 1m

Furthermore,

I = 1kA

R = 1mΩ

V = IR = ( 1kA )( 1mΩ )

This relatively simple expression can be solved with ease if we are familiar with metric prefix values. A list some common metric prefixes and their associated values provided below:

Metric Prefix

Symbol

Power of Ten

Value

femto             f   10^-15             one-quadrillionth

pico                                        p                10^-12                    one-trillionth

nano                                       n                10^-9                       one-billionth

micro                                      µ                10^-6                  one-millionth

milli                                        m               10^-3                      one-thousandth

centi                                       c                10^-2                  one-hundredth

deci                                        d                10^-1                  one-tenth

kilo                                         k                10³                  one thousand

mega                                      M               10⁶                   one million

giga                                        G               10⁹                   one billion

tera                                         T               10¹²                 one trillion

A thorough working-knowledge of these prefixes should be committed to memory prior to learning the SI units that commonly accompany them ( Ex. millivolts = mV ).