This post reviews some of the basic quantities and units of measure used in electronics. If you are already comfortable with the meaning of quantities such as 9 volts, 3 mA, 12k ohms and 100 Watts, this is will be a little basic.
What Is Electricity?
To understand electricity, we begin with electric charge, a basic property of matter.
The key charge-carrying particles are:
- protons — positive charge
- electrons — negative charge
In most materials, positive and negative charges balance, so nothing electrical appears to happen. But when charges become unbalanced, they begin to move to restore equilibrium.
This movement of electric charge is what we call electricity.
In metal wires, the moving charges are almost always electrons. A battery creates the conditions that cause these electrons to flow through a circuit.
That flow is the basis of every electrical device, from LEDs to motors.
To describe what’s happening in a circuit, we use four key ideas:
- current — flow of charge
- voltage — the push driving the flow
- resistance — opposition to the flow
- power — rate of energy use
We’ll explore these by building simple circuits and measuring them directly.
Measuring Electricity
Electrical quantities have standard units, just like distance or time.
A fundamental unit is the coulomb (C), which measures quantity of electric charge. In practice, however, electronics rarely uses coulombs directly—we usually work with current (charge flow per second) instead.
The most common units are:
Current and Amperes
Current is the flow of electric charge.
It is measured in amperes (amps), symbol I.
One ampere means a certain amount of charge passes a point each second (specifically, one coulomb per second). More current means more charge flowing.
Voltage and Volts
For charge to move, it needs a push, called voltage.
Voltage is measured in volts (V). A battery provides this push, driving current through a circuit.
Resistance and Ohms
Materials resist the flow of charge. This is called resistance.
Resistance is measured in ohms (Ω) and represented by R. Components called resistors are used to control current.
Power and Watts
When current flows, energy is used. The rate of this energy use is power.
Power is measured in watts (W). A higher wattage device uses more electrical energy.
Understanding Electrical Prefixes
When working with electricity, the numbers we encounter can be very large or very small. Writing all those zeros quickly becomes awkward. To make things easier, scientists and engineers use standard prefixes that represent powers of ten.
You have probably already seen some of these. For example, the word kilometer means one thousand meters. Electronics uses the same idea.
A prefix placed before a unit simply tells us to multiply the unit by a certain power of ten.
For example:
- kilovolt (kV) means one thousand volts
- milliamps (mA) means one thousandth of an amp
- megaohm (MΩ) means one million ohms
These prefixes appear constantly in electronics because many circuits involve very small currents and very large resistances.
Common Prefixes Used in Electronics
| Prefix | Symbol | Meaning | Power of Ten |
| giga | G | one billion | 109 |
| mega | M | one million | 106 |
| kilo | k | one thousand | 103 |
| (none) | — | one | 100 |
| milli | m | one thousandth | 10-3 |
| micro | µ | one millionth | 10-6 |
| nano | n | one billionth | 10-9 |
| pico | p | one trillionth | 10-12 |
These are the prefixes you will encounter most often in basic electronics.
Examples with Volts
Voltage often appears with prefixes.
Examples:
- 5 V – five volts
- 12 V – a common battery voltage
- 1 kV – one thousand volts = 1000 V
- 3 mV – three thousandths of a volt = 0.003 V
Small electronic signals are often measured in millivolts.
Examples with Current (Amps)
Electric current in small circuits is often quite small, so prefixes are used frequently.
Examples:
- 2 A – two amps
- 500 mA – five hundred thousandths of an amp = 0.5 A
- 20 µA – twenty millionths of an amp = 0.000002 A
Examples with Resistance (Ohms)
Resistors are often labeled using kiloohms or megaohms.
Examples:
- 220 Ω – two hundred twenty ohms
- 1 kΩ – one thousand ohms = 1,000 ohms
- 10 kΩ – ten thousand ohms = 10,000 ohms
- 1 MΩ – one million ohms = 1,000,000 ohms
Why Prefixes Matter
Using prefixes keeps numbers compact and readable. So use a prefix
0.000002 A = 2 μA
which is much easier to read.
As you work through the experiments in this series, you will see these prefixes often on:
- digital multimeter displays
- resistor labels
- power supply settings
- electronic component specifications
Becoming comfortable with them is one of the first steps toward reading and understanding electrical measurements.
Optional Practice Exercises: Working with Electrical Prefixes
The following exercises are optional practice problems. They are not part of the lab work, but they are helpful for becoming comfortable with the prefixes used in electronics. The goal is simply to practice reading and converting values written with prefixes.
Convert the following to volts: 3 kV, 25 mV
Convert the following to amps: 750 mA, 40 µA
Convert the following to ohms: 5 kΩ, 2.2 MΩ
Rewrite the following value using a prefix: 2000 V, 0.003 A, 47000Ω
Answers to the Optional Practice Exercises
3 kV=3000 V, 25 mV=0.025 V, 750 mA=0.75 A, 40 µA=0.000040 A, 5 kΩ=5000Ω, 2.2 MΩ=2,200,000Ω, 2000 V=2 kV, 0.003 A=3 mA, 47000Ω=47 kΩ
If you found some of these tricky, that is normal at first. With a little practice, recognizing and converting prefixes becomes very natural, and you will begin to read electrical values almost instantly.