Electromagnetic Spectrum
The electromagnetic spectrum is the complete range of electromagnetic waves that transfer energy from one place to another without transferring matter:contentReference[oaicite:1]{index=1}.
- All electromagnetic waves travel at a speed of 3.0 × 108 m/s in a vacuum.
- They can travel through vacuum — no medium required.
- They are all transverse waves.
- The energy they transfer depends on their wavelength.
- Shorter wavelength → higher frequency → higher energy.
Order of the Electromagnetic Spectrum
From longest wavelength to shortest (lowest to highest frequency):
Radio → Microwave → Infra-red → Visible → Ultraviolet → X-rays → Gamma rays
Remember: “Rabbits Mate In Very Unusual eXpensive Gardens.”
Regions, Typical Uses & Effects
| Region | Typical Uses | Harmful Effects (if excessive) |
|---|---|---|
| Radio waves | Radio & TV transmission, astronomy, RFID | Generally safe at normal exposure |
| Microwaves | Mobile phones, microwave ovens, satellite communication | Can cause internal heating of body cells |
| Infra-red | Remote controls, heaters, thermal imaging, optical fibre | Skin burns |
| Visible light | Vision, photography, illumination | Bright light can damage eyes |
| Ultraviolet | Security marking, detecting fake notes, sterilising water | Skin cancer, eye damage |
| X-rays | Medical imaging, security scanners | Cell mutation or damage |
| Gamma rays | Sterilising food and medical tools, cancer detection and treatment | Severe cell damage, DNA mutation |
Key Equations
v = f × λ where v = speed (m/s), f = frequency (Hz), λ = wavelength (m).
In a vacuum: v = 3.0 × 108 m/s
Analogue & Digital Signals
- Analogue signal — continuous signal representing a physical quantity (e.g. sound wave).
- Digital signal — discrete pulses that represent binary data.
- Advantages of digital: higher data rates, easier error correction, and longer transmission distance:contentReference[oaicite:2]{index=2}.
Everyday Communication Applications
- Mobile phones and Wi-Fi use microwaves — can pass through walls with small antennas.
- Bluetooth uses radio waves — passes through walls but weakens slightly.
- Optical fibres use visible or infra-red light — glass is transparent to these, allowing high-speed data transfer.
Exam Tips
- All EM waves have the same speed in vacuum but differ in wavelength and frequency.
- Energy ∝ frequency (higher frequency → higher energy).
- State safety precautions: limit X-ray exposure, wear UV-protective eyewear, and use microwave shielding.
- Remember: Gamma rays have the shortest wavelength and highest energy.
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