Have you noticed some strange things about the notation yet? If you’re observant, you have! Why, you might ask, are italics sometimes used, and sometimes not used? Something should be said early in this course about notation, because it can get confusing with all the different symbols and abbreviations. Sometimes, symbols and abbreviations appear in italics, and sometimes they do not. You’ll see subscripts often, and sometimes even they are italicized! Here are some rules that apply to notation in electricity and electronics:
- Symbols for specific units, such as volts, amperes, and ohms, are not italicized.
- Symbols for objects or components, such as resistors, batteries, and meters, are not italicized.
- Quantifying prefixes, such as “kilo-” or “micro-,” are not italicized.
- Labeled points in drawings might or might not be italicized; it doesn’t matter as long as a diagram is consistent with itself.
- Symbols for mathematical constants and variables, such as time, are italicized.
- Symbols for electrical quantities, such as voltage, current, resistance, and power, are italicized.
- Symbols and abbreviations for modifiers might or might not be italicized; it doesn’t matter as long as a document is consistent with itself.
- Numeric subscripts are not italicized.
- For nonnumeric subscripts, the same rules apply as for general symbols.
Some examples are R (not italicized) for resistor, R (italicized) for resistance, P (italicized) for power, W (not italicized) for watts, V (not italicized) for volts, E or V (italicized) for voltage, A (not italicized) for amperes, I (italicized) for current, f (italicized) for frequency, and t (italicized) for time.
Once in a while you will see the same symbol italicized in one place and not in another—in the same circuit diagram or discussion! We might, for example, talk about “resistor number 3” (symbolized R3), and then later in the same paragraph talk about its value as “resistance number 3” (Symbolized R3). Still later we might talk about “the nth resistor in a series connection” (Rn) and then “the nth resistance in a series combination of resistances” (Rn).
These differences in notation, while subtle (and, some people will say, picayune) are followed in this book, and they are pretty much agreed upon by convention. They are important because they tell the reader exactly what a symbol stands for in a diagram, discussion, or mathematical equation.
“Resistor” and “resistance” are vastly different things—as different from each other as a garden hose (the object) and the extent to which it impedes the flow of water (the phenomenon). With this in mind, let us proceed!