A History of Sending Messages with Waves
Humans have always wanted to send messages over long distances. For thousands of years, people used fire signals and drumbeats. These early methods relied on light and sound — both forms of waves. Over the past two centuries, scientists and engineers figured out how to use waves to carry detailed information, like voices and images, across the entire planet.
From Morse code to streaming video, every step forward depended on one big idea: waves can carry information from one place to another. But how exactly does a wave "carry" a message? That is the question this lesson explores.
Core Principles of Wave-Based Communication
Before we can understand how waves carry information, we need a few key ideas. A wave is a disturbance that transfers energy from one place to another without moving matter along with it. Waves have properties like frequency (how many wave cycles pass a point each second), wavelength (the distance from one wave crest to the next), and amplitude (the height of the wave, related to its energy). These properties can be changed, or modulated, to encode information onto the wave.
Waves Transfer Energy, Not Matter
Encoding Means Adding a Pattern
Analog vs. Digital Signals
Many Types of Waves Carry Information
How Information Rides on a Wave
The diagram below shows two common ways to encode information onto a wave. The top row shows an analog signal, where the wave smoothly changes its amplitude to match the original sound. The bottom row shows a digital signal, where the wave is converted into a series of ON/OFF pulses (1s and 0s). Notice how the digital signal has only two levels. This makes it easier to tell apart even when noise is added.
Look at the analog wave first. Its height changes continuously — it can be any value between the highest and lowest points. Now look at the digital wave. It only has two positions: high (1) and low (0). When noise or interference messes up the signal a little, the analog wave gets permanently distorted. But the digital wave can still be read correctly because the receiver only needs to decide: is this a 1 or a 0? This is a key reason why digital signals are more reliable than analog signals for transmitting information.
The Wave Equation — Connecting Speed, Frequency, and Wavelength
Waves that carry information travel at a certain speed. That speed depends on the type of wave and the material it moves through. There is a simple equation that connects a wave's speed, frequency, and wavelength.
You can rearrange this equation to solve for any variable. If you know the speed and wavelength, you can find frequency. If you know the speed and frequency, you can find wavelength.
For electromagnetic waves (like light, radio, and microwaves), the speed in empty space is always about 300,000,000 m/s — that's the speed of light! Sound waves are much slower. Sound travels through air at about 343 m/s.
The Electromagnetic Spectrum — Waves for Every Job
Not all electromagnetic waves are the same. They come in a wide range of frequencies and wavelengths. Scientists organize them into the electromagnetic spectrum (a chart of all electromagnetic wave types arranged by frequency and wavelength). Different parts of the spectrum are useful for different kinds of information transfer.
Notice the pattern (Crosscutting Concept): waves with higher frequencies can generally carry more information per second. This idea is called bandwidth (the range of frequencies a channel can use, which determines how much data it can carry per second). A fiber optic cable using light can carry far more data than a copper wire carrying electrical signals, mostly because light operates at enormously higher frequencies (around 1014 Hz) compared to electrical signals in copper (around 109 Hz). This higher carrier frequency allows a much wider bandwidth.
Worked Example — Finding the Wavelength of a Radio Station
Let's use the wave equation to solve a real problem. This example connects to MS-PS4-1 (using mathematical representations to describe waves).
Analog vs. Digital — Strengths and Limitations
Both analog and digital signals can carry information using waves. But they have different strengths and weaknesses. This connects to NGSS performance expectation MS-PS4-3, which asks you to support the claim that digitized signals are a more reliable way to encode and transmit information.
| Feature | Analog Signal | Digital Signal |
|---|---|---|
| Signal shape | Smooth, continuous wave | Square pulses (ON/OFF, 1/0) |
| Effect of noise | Noise adds permanently to the signal; hard to remove | Noise can be filtered; receiver only checks for 1 or 0 |
| Copying quality | Copies lose quality (like photocopying a photocopy) | Copies are identical (1s and 0s don't degrade) |
| Data capacity | Limited; one channel per signal | Can compress and multiplex many signals together |
| Example | Old vinyl records, AM radio | MP3 files, streaming video, Wi-Fi |
Looking Ahead — Waves in Modern Technology
The ideas you've learned in this lesson are the foundation for many advanced technologies. As you move into high school science, you'll explore these ideas in much more detail.
| What You Learn Now | Where It Leads |
|---|---|
| Waves carry information by changing amplitude or frequency | High school physics: modulation techniques (AM and FM), signal processing |
| Digital signals use 1s and 0s | Computer science: binary code, data compression, encryption |
| Electromagnetic spectrum has many types of waves | Advanced physics: quantum mechanics, photon energy, spectroscopy |
| v = f × λ relates wave properties | Engineering: antenna design, telecommunications, medical imaging |
Today's 5G cell networks, satellite internet, and even self-driving cars all depend on waves transmitting information. Engineers carefully choose which type of wave to use for each job. They consider cause and effect (Crosscutting Concept): what happens to the signal when it passes through buildings, rain, or long distances? Understanding wave behavior helps engineers solve these real-world problems.
Practice Problems
Lesson Summary
Waves are the foundation of modern communication. Waves transfer energy without transferring matter, and engineers encode information by changing a wave's amplitude, frequency, or timing. The wave equation (v = f × λ) connects speed, frequency, and wavelength, helping us understand how different waves behave. The electromagnetic spectrum includes radio waves, microwaves, infrared, visible light, and more — each type suited to specific communication tasks.
Digital signals (patterns of 1s and 0s) are more reliable than analog signals (smooth, continuous waves) because digital signals can be reconstructed even after noise is added. This is why most modern technology — from Wi-Fi and cell phones to fiber optic internet — uses digital encoding. Waves with higher carrier frequencies offer greater bandwidth, allowing more information to be transmitted each second. Understanding waves and how they carry information is essential for the technologies you use every day.