Chapter 3: The Electromagnetic Spectrum
All electromagnetic waves travel at the same speed, but they come in a breathtaking variety of frequencies and wavelengths. When we arrange them in order, we get the electromagnetic spectrum.
3.1 The Seven Bands of the Spectrum
| Band | Wavelength | Frequency | Key Applications |
|---|---|---|---|
| Radio Waves | 1 mm – 100 km | 3 kHz – 300 GHz | AM/FM radio, TV, walkie-talkies |
| Microwaves | 1 mm – 30 cm | 1 GHz – 300 GHz | Wi-Fi, radar, microwave ovens, GPS |
| Infrared | 700 nm – 1 mm | 300 GHz – 430 THz | TV remotes, thermal cameras |
| Visible Light | 400 – 700 nm | 430 – 770 THz | Human vision, photography |
| Ultraviolet | 10 – 400 nm | 770 THz – 30 PHz | Sunburn, sterilization |
| X-rays | 0.01 – 10 nm | 30 PHz – 30 EHz | Medical imaging, security |
| Gamma Rays | < 0.01 nm | > 30 EHz | Cancer treatment, nuclear physics |
📊 Diagram: The electromagnetic spectrum arranged from longest wavelength (radio) to shortest (gamma rays), with common objects for scale (buildings, humans, cells, atoms, nuclei).
3.2 Radio Waves: The Giants
Radio waves have the longest wavelengths — from about a millimeter to hundreds of kilometers! They are all around you right now, carrying music, phone calls, and data.
3.3 Microwaves: The Versatile Middle Ground
Microwaves are shorter radio waves, typically between 1 mm and 30 cm. Your Wi-Fi router, GPS system, Bluetooth earbuds, and weather radar all use microwaves.
3.4 Infrared: The Heat You Feel
Every warm object emits infrared radiation. When you feel the warmth of the sun on your skin, you are detecting infrared.
🌍 Real World: Firefighters use infrared cameras to see through smoke and find people trapped in burning buildings. The human body emits infrared radiation, making people visible in complete darkness.
3.5 Visible Light: Our Window to the World
Visible light is the tiny sliver of the EM spectrum that our eyes can detect, ranging from red (~700 nm) to violet (~400 nm).
💡 Fun Fact: If the entire EM spectrum were a piano keyboard stretching from New York to Los Angeles, the visible light portion would be less than one key! We are essentially blind to 99.99% of the electromagnetic universe.
3.6 Ultraviolet
Ultraviolet causes sunburn and can damage DNA, but it also kills bacteria and makes materials glow under black lights.
3.7 X-rays
X-rays have enough energy to pass through soft tissue but get absorbed by bone and metal, making medical imaging possible.
3.8 Gamma Rays
Gamma rays have the shortest wavelengths and highest energies. In medicine, focused gamma rays destroy cancer cells. In the universe, gamma ray bursts are the most energetic events since the Big Bang.