About Electricity


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.


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 withAC (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 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 is a measurement of the rate at which an electrical device convertsenergy from one form to another. Power is measured in watts (W). 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 (W) = Voltage (V) × Current (A)


These prefixes are universally used to scale units:

Multiple   prefix     symbol

1012            tera           T

109             giga           G

106            mega         M

103            kilo             k

10-3          milli          m

10-6          micro        µ

10-9          nano        n

10-12         pico         p

10-15      femto         f




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