Electromagnetic Spectrum
Year 8 🌊 Waves & Optics Name and order the EM spectrum; describe key properties and uses.
📡 The Electromagnetic Spectrum
All electromagnetic (EM) waves travel at the same speed in a vacuum — the speed of light! They differ only in wavelength and frequency.
⚡ Key Property
$$c = f\lambda = 3 \times 10^8 \text{ m/s (in vacuum/air)}$$ EM waves are transverse waves — unlike sound, they can travel through a vacuum (empty space). This is how energy from the Sun reaches us!
| 📊 Property | 📝 What it means |
|---|---|
| All travel at c = 3×10⁸ m/s | In a vacuum, every EM wave has the same speed |
| Transverse waves | Vibrations perpendicular to direction of travel |
| Do not need a medium | Can travel through vacuum (empty space) |
🌈 Ordering the Spectrum
From longest to shortest wavelength (lowest to highest frequency/energy):
| 📡 Wave type | 📏 Wavelength range | 🔍 Example use |
|---|---|---|
| 📻 Radio waves | 1 mm → 100,000 km | TV, radio broadcasts |
| 📱 Microwaves | 1 mm → 1 m | Microwave ovens, mobile phones |
| 🌡️ Infrared (IR) | 700 nm → 1 mm | Remote controls, thermal cameras |
| 👁️ Visible light | 400 → 700 nm | Seeing, photography |
| 🔆 Ultraviolet (UV) | 10 → 400 nm | Sun tanning, sterilisation |
| ☢️ X-rays | 0.01 → 10 nm | Medical imaging, security scanners |
| ☢️ Gamma rays | < 0.01 nm | Cancer treatment, sterilising food |
⚠️ Uses and Hazards
Different parts of the EM spectrum have specific uses AND potential hazards.
| 🌊 Wave | ✅ Useful for | ⚠️ Hazard |
|---|---|---|
| Microwaves | Cooking food, 5G networks | Internal tissue heating |
| Infrared | Night vision, physiotherapy | Burns skin at high intensity |
| UV | Vitamin D production, detecting fake notes | Skin cancer, eye damage |
| X-rays | See bones, luggage scanning | Cell damage, cancer (ionising) |
| Gamma | Kill cancer cells, sterilise equipment | Cell/DNA damage, cancer |
X-rays and gamma rays are ionising radiation — they can knock electrons out of atoms, damaging DNA and cells. Always use the minimum necessary dose in medical imaging!
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📡 EM Wave Calculator (c = fλ)
💡 All EM waves travel at c = 3 × 10⁸ m/s in vacuum