Let’s spend a bit of time discussing electricity, since you’ll soon be buildingelectronic circuits with your Arduino projects. In simple terms, *electricity* is aform of energy that we can harness and convert into heat, light, movement,and power. Electricity has three main properties that will be important tous as we build projects: current, voltage, and power.

*Current*

The flow of electrical energy through a circuit is called the *current*. Electricalcurrent flows through a *circuit* from the positive side of a power source such as a battery, to the negative side of the power source. This is knownas *direct current (DC)*. For the purposes of this book, we will not deal with*AC (alternating current)*. In some circuits, the negative side is called *ground(GND)*. Current is measured in *amperes* or “amps” (*A*). Small amountsof current are measured in *milliamps (mA)*, where 1,000 milliamps equal1 amp.

*Voltage*

*Voltage* is a measure of the difference in potential energy between a circuitpositive and negative ends. This is measured in *volts (V)*. The greater thevoltage, the faster the current moves through a circuit.

*Power*

*Power* is a measurement of the rate at which an electrical device convertsenergy from one form to another. Power is measured in *watts *. Forexample, a 100 W light bulb is much brighter than a 60 W bulb becausethe higher-wattage bulb converts more electrical energy into light.A simple mathematical relationship exists among voltage, current,and power:

Power = Voltage (V) × Current (A)

These prefixes are universally used to scale units:

Multiple prefix symbol

10^{12 } tera T

10^{9 } giga G

10^{6 } mega M

10^{3 } kilo k

10^{-3 } milli m

10^{-6 } micro µ

10^{-9} nano n

10^{-12} pico p

10^{-15} femto f