This chapter is not intended in any way as a substitution for a proper education in electrical engineering! We will go over some of the fundamentals in the context of the BeagleBone so that the rest of the chapter makes sense.
Electricity has three basic properties, namely, voltage, current, and resistance. Using a water analogy, voltage can be considered as the pressure and current can be considered as the rate of the water flow. Voltage is measured in volts and is written as V and current is measured in amperes and is written as either amp or A. For many of our purposes, it is convenient to measure current in milliamp or mA. This is 1/1000th of an amp. Tie this to the water analogy and amperes is the rate of charge per second. Resistance is what lets us control the amount of current or voltage. Resistance is measured in ohms.
Resistance, voltage, and current are related to each other by Ohm's law (http://en.wikipedia.org/wiki/Ohm...