What Is Electricity?
This first post will cover some basic concepts and definitions but unfortunately no experiments. This will be the only one without any hands on work. I promise.
To understand electricity, we begin with a property of matter called electric charge.
Electric charge is a basic characteristic of certain subatomic particles. The two most important particles for electricity are:
- protons, which carry positive charge
- electrons, which carry negative charge
In most everyday materials the total positive and negative charge is balanced. When the charges are balanced, nothing electrical appears to be happening.
But sometimes charges become separated or unbalanced. When this happens, nature tends to restore the balance. Charges begin to move.
This movement of electric charge is what we call electricity.
In metal wires, the moving charges are almost always electrons. When a battery is connected to a circuit, it creates a situation in which electrons begin to move through the wire and the components attached to it.
That motion of charge is the foundation of every electrical device, from a tiny LED to a large electric motor.
To describe what is happening in an electrical circuit, we use four important ideas:
- current — how much charge is flowing
- voltage — what pushes the charge through the circuit
- resistance — what opposes the flow of charge
- power — how fast electrical energy is being used
In the posts that follow, we will build simple circuits and measure these quantities directly. By doing so, you will see how the motion of electric charge produces the electrical behavior we observe in real circuits.
Measuring Electricity
To understand and describe what is happening in an electrical circuit, we need ways to measure the important electrical quantities. Just as we measure distance in meters or feet and time in seconds, electricity has its own units of measurement.
Three of the most important units are amperes, volts, and ohms.
Current and Amperes
When electric charge moves through a wire, we call this motion electric current.
The amount of current flowing in a circuit is measured in amperes. Because the word is a little long, it is almost always shortened to amps. We use the symbol i or I.
If a wire carries more amps, it means more electric charge is flowing each second through the wire.
Voltage and Volts
For charge to move, something must push it through the circuit. That push is called voltage.
A battery provides voltage between its two terminals. When a circuit is connected, this voltage pushes charge through the wires and components.
Voltage is measured in volts and we use the symbol V.
Different power sources provide different voltages. For example, a small battery provides only a few volts, while household electrical outlets provide much higher voltage.
Resistance and Ohms
Materials and electronic components do not allow charge to move freely. They oppose the flow of current to different degrees.
This opposition is called resistance and is measured in ohms. The general symbol for resistance is R and the unit of measure carries the symbol Ω (Greek letter omega).
Many electronic components are designed specifically to provide resistance. These components are called resistors, and they are used to control how much current flows in a circuit.
Power and Watts
When electricity flows through a device, energy is being used. A lamp produces light, a heater produces heat, and a motor produces motion. The rate at which electrical energy is used is called power. Power is measured in watts and uses the symbol W.
You may have seen this unit when buying light bulbs or appliances. For example, an older style incandescent bulb might be labeled 60 watts or 100 watts.
A 100-watt bulb uses more electrical power than a 60-watt bulb, and it produces more light as a result.
Many appliances are rated by the number of watts they use. This number tells us how much electrical energy the device uses while operating.
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. Instead of writing
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.