3.3 Electromagnetic Spectrum
🔊 Radio Waves (≈10³–10¹⁰ Hz)
Think of radio waves as the long‑distance runners of the spectrum. They travel far, can go through walls, and are great for carrying information over long distances.
- 📻 Radio & TV transmissions – the classic broadcast you tune into.
- 🌌 Astronomy – radio telescopes listen to distant stars and galaxies.
- 🔑 RFID tags – the small chips that let you open doors or track items.
Exam tip:
- Remember the long wavelength, low frequency nature of radio waves.
- Use the analogy of runners to recall why they can travel far.
- List one example for each typical use.
🌐 Microwaves (≈10¹¹–10¹⁴ Hz)
Microwaves are like the middle‑aged sprinters – fast enough to heat things quickly but still able to bounce off surfaces.
- 📺 Satellite TV – signals from orbit to your dish.
- 📱 Mobile phones – the waves that carry your calls and data.
- 🍔 Microwave ovens – they excite water molecules to heat food.
Exam tip:
- Recall the frequency range and that microwaves heat by exciting water.
- Use the sprinter analogy to remember their speed.
- Give one example of each use.
🌡️ Infrared (≈10¹⁴–10¹⁶ Hz)
Infrared waves are like the warm glow of a campfire – they’re close enough to feel heat but invisible to the eye.
- 🍖 Electric grills – heat food from the inside out.
- 📱 Remote controls – send short‑range IR signals to TVs.
- 🚨 Intruder alarms – use IR beams to detect motion.
- 🌡️ Thermal imaging – cameras that show heat patterns.
- 📡 Optical fibres – guide IR light for data transmission.
Exam tip:
- Remember that IR is heat‑related and invisible.
- Use the campfire analogy to recall its warmth.
- List at least three typical uses.
🌈 Visible Light (≈4×10¹⁴–7.5×10¹⁴ Hz)
Visible light is the part of the spectrum we can see – it’s the rainbow that makes the world colourful.
- 👀 Vision – our eyes detect visible light.
- 📷 Photography – cameras capture light to create images.
- 💡 Illumination – lamps and LEDs light up rooms.
Exam tip:
- Recall the visible range and that it’s the only part humans can see.
- Use the rainbow analogy to remember its role in colour.
- Give one example for each use.
☀️ Ultraviolet (≈10¹⁶–10¹⁷ Hz)
Ultraviolet waves are like the invisible sunburn – they’re energetic enough to break bonds but still safe in small doses.
- 🔒 Security marking – UV inks reveal hidden patterns.
- 💰 Detecting fake bank notes – UV light shows special features.
- 💧 Sterilising water – UV kills bacteria and viruses.
Exam tip:
- Remember that UV is more energetic than visible light.
- Use the sunburn analogy to recall its effects.
- List the three typical uses.
⚛️ X‑Rays (≈10¹⁸–10²⁰ Hz)
X‑rays are like the high‑speed detectives – they can see inside objects that are normally opaque.
- 🏥 Medical scanning – X‑ray images show bones and tissues.
- 🛂 Security scanners – detect hidden items on airport belts.
Exam tip:
- Recall that X‑rays have very high frequency and can penetrate matter.
- Use the detective analogy to remember their imaging role.
- Give one example of each typical use.
💥 Gamma Rays (≈10²⁰–10²⁴ Hz)
Gamma rays are the ultimate high‑energy waves – they’re so powerful they can even break atoms.
- 🍽️ Food sterilisation – gamma rays kill bacteria in packaged food.
- 🛠️ Medical equipment sterilisation – ensures devices are safe.
- 🩺 Cancer detection & treatment – used in imaging and radiotherapy.
Exam tip:
- Remember that gamma rays are the most energetic part of the spectrum.
- Use the atom‑breaking analogy to recall their power.
- List the three typical uses.
| Region | Typical Uses | Frequency Range (Hz) |
|---|
| Radio Waves | Broadcast, astronomy, RFID | ≈\$10^3\$–\$10^{10}\$ |
| Microwaves | Sat TV, mobile phones, ovens | ≈\$10^{11}\$–\$10^{14}\$ |
| Infrared | Grills, remotes, alarms, thermal imaging, fibres | ≈\$10^{14}\$–\$10^{16}\$ |
| Visible Light | Vision, photography, illumination | ≈\$4\times10^{14}\$–\$7.5\times10^{14}\$ |
| Ultraviolet | Security marking, fake note detection, sterilising water | ≈\$10^{16}\$–\$10^{17}\$ |
| X‑Rays | Medical imaging, security scanners | ≈\$10^{18}\$–\$10^{20}\$ |
| Gamma Rays | Food & equipment sterilisation, cancer treatment | ≈\$10^{20}\$–\$10^{24}\$ |