LIBRARYUnits and prefixes.

Electronics runs on a small set of quantities and a ladder of prefixes. Get comfortable with volts, amps, and ohms, and with reading 4.7 uF or 5.1 kΩ off a part, and every later guide has a foundation to stand on. This is that foundation.

What are the basic units?

A volt (V) measures electrical push, the pressure that moves charge. An amp (A) measures current, the rate charge flows. An ohm (Ω) measures resistance, how strongly a material fights that flow. A farad (F) measures capacitance, how much charge a part stores per volt. A watt (W) measures power, the rate energy is used. These five cover almost everything on a small board. Each is an SI unit with a fixed international definition set by the 2019 revision of the SI (BIPM 2019).

What do the prefixes mean?

A prefix scales a unit up or down by powers of ten, so you rarely write a long string of zeros. Going down: milli (m) is a thousandth, micro (u) a millionth, nano (n) a billionth, pico (p) a trillionth. Going up: kilo (k) is a thousand, mega (M) a million. So 4.7 uF is 4.7 millionths of a farad, and 5.1 kΩ is 5100 ohms. Read the prefix first and the value stops being intimidating.

Reading a real part value

On a One Thousand Drones bill of materials you meet values like 100 nF, 4.7 uF, and 5.1 kΩ next to real parts. A 100 nF capacitor sits beside almost every chip. A 5.1 kΩ resistor sets a USB-C port's role. Same units, same ladder, on parts you actually order and solder.