Electronics Cookbook

Chapter 1. Theory

1.0 Introduction

Although this book is fundamentally about practice rather than theory, there are a few theoretical aspects of electronics that are almost impossible to avoid.

In particular, if you understand the relationship between voltage, current, and resistance many other things will make a lot more sense.

Similarly, the relationship between power, voltage, and current crops up time and time again.

1.1 Understanding Current

Problem

You want to understand what is meant by current in electronics.

Solution

As the word current suggests, the meaning of current in electronics is close to that of the current in a river. You could think of the strength of the current in a pipe as being the amount of water passing a point in the pipe every second. This might be measured in so many gallons per second.

In electronics, current is the amount of charge carried by electrons passing a point in a wire per second (Figure 1-1). The unit of current is the ampere, abbreviated as amp or as unit symbol A.

Figure 1-1. Current flowing through a wire

Discussion

For many circuits, one whole amp is quite a large current, so you will see the units of mA (milliamp, a thousandth of an amp) a lot.

See Also

For a list of units and unit prefixes such as mA, see Appendix D.

To learn more about current in a circuit, see Recipe 1.4.

1.2 Understanding Voltage

Problem

You want to ...