3.3 Electromagnetic Spectrum
The electromagnetic (EM) spectrum is a continuous range of electromagnetic waves characterised by their wavelength λ (or frequency f). All EM waves travel at the same speed in vacuum
c ≈ 3.0 × 10⁸ m s⁻¹
and at essentially the same speed in air. Because they are oscillating electric‑magnetic fields, EM waves do not require a material medium (unlike sound).
The fundamental relationship between wavelength, frequency and speed is
c = λ f or f = c/λ
For the IGCSE the spectrum is ordered by increasing frequency (decreasing wavelength):
R M I V U X γ – Radio, Microwaves, Infra‑red, Visible, Ultraviolet, X‑rays, Gamma‑rays.
Summary Table – Typical Uses (Cambridge IGCSE 0625) and Health Effects
| Region | Wavelength / Frequency | Typical Uses
(syllabus reference in brackets) | Harmful Effects (if any) |
|---|
| Radio waves | λ ≈ 10³ m – 10⁻² m (ƒ ≈ 3 × 10⁵ – 3 × 10⁹ Hz) | - Radio & TV broadcasting (AM, FM, DAB, digital TV) (s 4.1)
- Satellite communication – GPS, satellite TV uplink/downlink (s 4.1)
- Bluetooth, short‑range wireless links (s 4.1)
- Radio‑frequency identification (RFID) tags (s 4.1)
- Radio astronomy – detection of natural radio emission from space (s 4.1)
| Generally non‑ionising; prolonged exposure to very high‑power transmitters can cause heating of tissue (e.g., strong radar), but ordinary broadcast levels are safe. |
| Microwaves | λ ≈ 10⁻² m – 10⁻⁴ m (ƒ ≈ 3 × 10⁹ – 3 × 10¹¹ Hz) | - Satellite television downlink (≈10–12 GHz) (s 4.1)
- Mobile‑phone networks (900 MHz, 1800 MHz, 2.1 GHz, 3.5 GHz) (s 4.1)
- Microwave ovens (2.45 GHz) (s 4.1)
- Radar & air‑traffic control (s 4.1)
- Wi‑Fi (2.4 GHz & 5 GHz) (s 4.1)
| Microwaves are non‑ionising but can heat biological tissue; excessive exposure can cause burns or cataracts. |
| Infra‑red (IR) | λ ≈ 10⁻⁴ m – 7 × 10⁻⁷ m (ƒ ≈ 3 × 10¹¹ – 4 × 10¹⁴ Hz) | - IR heating – grills, saunas, industrial panels (s 4.1)
- Remote controls (IR LEDs) (s 4.1)
- Thermal‑imaging & night‑vision cameras (s 4.1)
- Optical‑fibre communication (1.3 µm & 1.55 µm windows) (s 4.1)
- Medical thermography (s 4.1)
| IR is non‑ionising; intense IR radiation can cause skin burns. |
| Visible light | λ ≈ 7 × 10⁻⁷ m – 4 × 10⁻⁷ m (400 nm – 700 nm) (ƒ ≈ 4 × 10¹⁴ – 7.5 × 10¹⁴ Hz) | - Human (and many animal) vision (s 4.1)
- Photography, video recording & projection (s 4.1)
- Illumination – lamps, LEDs, lasers (s 4.1)
- Colour displays – LCD, OLED, LED screens (s 4.1)
| Bright visible light can cause retinal damage; prolonged exposure to intense sources (e.g., lasers) is hazardous. |
| Ultraviolet (UV) | λ ≈ 4 × 10⁻⁷ m – 10⁻⁸ m (10 nm – 400 nm) (ƒ ≈ 7.5 × 10¹⁴ – 3 × 10¹⁶ Hz) | - Security markings & anti‑counterfeit inks (invisible under normal light) (s 4.1)
- Bank‑note verification under UV lamps (s 4.1)
- UV‑C sterilisation (≈254 nm) (s 4.1)
- Fluorescence spectroscopy (s 4.1)
| UV‑B and UV‑C are ionising; they damage DNA, causing skin burns, cataracts and increased risk of skin cancer. |
| X‑rays | λ ≈ 10⁻⁸ m – 10⁻¹¹ m (0.01 nm – 10 nm) (ƒ ≈ 3 × 10¹⁶ – 3 × 10¹⁹ Hz) | - Medical imaging – radiography, CT scans, fluoroscopy (s 4.1)
- Security scanners at airports & ports (s 4.1)
- Crystallography & material analysis (s 4.1)
| Ionising radiation; can damage living cells and increase cancer risk. Protection (lead shielding, limiting exposure) is essential. |
| Gamma rays | λ < 10⁻¹¹ m ( < 0.01 nm) (ƒ > 3 × 10¹⁹ Hz) | - Sterilising food, medical equipment & pharmaceuticals (s 4.1)
- Cancer treatment – radiotherapy (s 4.1)
- Positron‑emission tomography (PET) imaging (s 4.1)
- Astronomical observations of supernovae, pulsars, γ‑ray bursts (s 4.1)
| Highly ionising; exposure can cause severe tissue damage and acute radiation sickness. Strict safety protocols are required. |
Detailed Uses – Core vs. Supplementary
Radio Waves (Core)
- Broadcasting: AM (medium wave), FM (VHF), DAB and digital TV use specific frequency bands.
- Satellite communication: GPS, satellite TV uplink/downlink, and some data links operate in VHF/UHF and L‑band ranges.
- Short‑range wireless: Bluetooth (2.4 GHz ISM band) and Wi‑Fi (2.4 GHz/5 GHz) are technically radio‑wave technologies.
- RFID: Passive tags exchange data with a reader using low‑frequency (125 kHz) or high‑frequency (13.56 MHz) radio waves.
- Radio astronomy: Large dish antennas detect natural radio emission from pulsars, gas clouds and distant galaxies.
Microwaves (Core)
- Satellite television: Downlink signals around 10–12 GHz are received by parabolic dish antennas.
- Mobile‑phone networks: Cellular systems allocate microwave bands (e.g., 900 MHz, 1800 MHz, 2.1 GHz, 3.5 GHz) for voice and data.
- Microwave ovens: A magnetron produces 2.45 GHz radiation; water molecules absorb it, heating food.
- Radar: Air‑traffic control and weather radars emit short microwave pulses to determine distance and speed.
- Wi‑Fi: 2.4 GHz and 5 GHz ISM bands provide short‑range high‑speed data links.
Infra‑red (IR) – Supplementary (advanced)
- Industrial & domestic heating (IR grills, saunas).
- Remote‑control devices using IR LEDs.
- Thermal‑imaging cameras for night‑vision, building surveys and medical diagnostics.
- Low‑loss windows (1.3 µm & 1.55 µm) in optical‑fibre communication.
- Physiotherapy lamps for wound healing.
Visible Light – Core
- Human (and many animal) vision – colour and detail perception.
- Photography, video recording and projection.
- Artificial illumination – incandescent bulbs, LEDs, lasers.
- Display technology – LCD, OLED and LED screens using red, green and blue sub‑pixels.
Ultraviolet (UV) – Core
- Security features – UV‑fluorescent inks on passports, bank‑notes and ID cards.
- Bank‑note verification under UV lamps.
- UV‑C sterilisation (≈254 nm) for water, air and surfaces.
- Fluorescence spectroscopy in chemical and biological analysis.
X‑rays – Core
- Medical imaging – radiographs, CT scans, fluoroscopy.
- Security scanning of luggage and cargo.
- Crystallography and material analysis (X‑ray diffraction).
Gamma Rays – Core
- Sterilising food, medical equipment and pharmaceuticals.
- Cancer treatment – radiotherapy with high‑energy γ‑beams.
- Positron‑emission tomography (PET) imaging.
- Astronomical observations of supernovae, pulsars and γ‑ray bursts.
Suggested Diagram
Figure 1 – Continuous electromagnetic spectrum
Draw a horizontal axis labelled either “Wavelength (m)” (decreasing to the right) or “Frequency (Hz)” (increasing to the right). Mark the seven regions (R M I V U X γ) and place one representative application inside each coloured band (e.g., “radio broadcast” in the radio‑wave region, “microwave oven” in the microwave region, etc.). This diagram can be reproduced on the board or inserted as a printed figure.