Properties and Uses of EM Waves

This lesson covers the properties and uses of each part of the electromagnetic spectrum — as required by AQA GCSE Combined Science Trilogy (8464), Physics Paper 2, section 6.2. You need to know at least one use for each type of EM wave and understand how properties such as wavelength and energy determine their applications.

---

Uses of Each Type of EM Wave

graph TD
    EM["Electromagnetic Spectrum — Uses"]
    EM --> R["Radio waves"]
    EM --> MW["Microwaves"]
    EM --> IR["Infrared"]
    EM --> VL["Visible light"]
    EM --> UV["Ultraviolet"]
    EM --> XR["X-rays"]
    EM --> GR["Gamma rays"]

    R --> R1["TV and radio broadcasting"]
    R --> R2["Bluetooth and Wi-Fi"]
    MW --> MW1["Satellite communication"]
    MW --> MW2["Cooking food (microwave ovens)"]
    IR --> IR1["Remote controls"]
    IR --> IR2["Thermal imaging / heating"]
    VL --> VL1["Photography / vision"]
    VL --> VL2["Fibre optic communication"]
    UV --> UV1["Fluorescent lamps"]
    UV --> UV2["Detecting forged banknotes"]
    XR --> XR1["Medical imaging (bones)"]
    XR --> XR2["Airport security scanners"]
    GR --> GR1["Cancer treatment (radiotherapy)"]
    GR --> GR2["Sterilising medical equipment"]

    style EM fill:#2c3e50,color:#fff
    style R fill:#e74c3c,color:#fff
    style MW fill:#e67e22,color:#fff
    style IR fill:#f1c40f,color:#333
    style VL fill:#2ecc71,color:#fff
    style UV fill:#3498db,color:#fff
    style XR fill:#9b59b6,color:#fff
    style GR fill:#34495e,color:#fff

Detailed Uses Table

EM wave	Uses	How it works
Radio waves	TV and radio broadcasting, Bluetooth, Wi-Fi	Radio waves carry encoded signals over long distances; aerials receive and decode the signal
Microwaves	Satellite communication, cooking food, mobile phones	Microwaves pass through the atmosphere to communicate with satellites; in ovens, microwaves are absorbed by water molecules in food, increasing their kinetic energy (heating the food)
Infrared (IR)	Remote controls, thermal imaging, heaters, fibre optics	IR is emitted by all warm objects; TV remotes send coded IR pulses; thermal cameras detect IR to show heat patterns
Visible light	Vision, photography, fibre optic communication, illumination	The only EM wave detectable by the human eye; fibre optics use total internal reflection to carry light signals
Ultraviolet (UV)	Fluorescent lamps, detecting forged banknotes, sun beds	UV causes some materials to fluoresce (glow); security features on banknotes are visible under UV light
X-rays	Medical imaging (bones and teeth), airport security	X-rays pass through soft tissue but are absorbed by dense materials (bone, metal), creating shadow images on a detector
Gamma rays (γ)	Sterilising medical instruments, cancer treatment (radiotherapy), sterilising food	Gamma rays can kill bacteria and cancer cells; in radiotherapy, a focused beam targets a tumour

Exam Tip (AQA 8464): Learn at least two uses for each type of EM wave. AQA frequently asks you to state a use and explain how the properties of that wave make it suitable for that application.

---

How Properties Determine Uses

Property	Implication	Example
Long wavelength (radio)	Can diffract around buildings and hills; travel long distances	Radio broadcasting over wide areas
Penetrating ability (X-rays, gamma)	Can pass through soft tissue or packaging	Medical imaging, security scanning
Absorbed by water molecules (microwaves)	Heats water-containing substances	Microwave ovens
Emitted by warm objects (IR)	Reveals temperature differences	Thermal imaging cameras
High energy / ionising (UV, X-rays, gamma)	Can damage or destroy cells	Cancer treatment, sterilisation
Travels in straight lines (visible, IR)	Can be guided along optical fibres	Telecommunications

---

Fibre Optics

Optical fibres use visible light or infrared to transmit data at very high speeds.

• Light enters one end of a thin glass fibre and undergoes total internal reflection repeatedly along the fibre.
• This allows signals to travel long distances with very little loss of energy.
• Used in broadband internet, telephone communication and medical endoscopes.

---

Absorption, Transmission and Reflection

When an EM wave meets a material, three things can happen:

Behaviour	What happens	Effect
Absorption	The wave's energy is transferred to the material (often as heat)	The material warms up
Transmission	The wave passes through the material	The material is transparent to that wavelength
Reflection	The wave bounces back from the surface	The wave changes direction

Different materials and wavelengths give different combinations of these three behaviours. For example, glass transmits visible light but absorbs ultraviolet.

---

Common Mistakes

Mistake	Correction
Saying "radio waves are used in microwave ovens"	Microwaves (not radio waves) are used in microwave ovens
Confusing infrared and ultraviolet	Infrared = heat, remote controls; Ultraviolet = fluorescence, sun burns
Not explaining why a particular EM wave is used	Always link the property of the wave to the application
Thinking gamma rays and X-rays cannot overlap	Their wavelength ranges can overlap — the distinction is based on origin, not wavelength alone

---

Summary

• Each type of EM wave has specific uses that depend on its wavelength, frequency, energy and penetrating ability.
• Radio waves: broadcasting, Wi-Fi. Microwaves: satellites, cooking. Infrared: remotes, thermal imaging. Visible light: vision, fibre optics. UV: fluorescence, security. X-rays: medical imaging. Gamma rays: radiotherapy, sterilisation.
• EM waves can be absorbed, transmitted or reflected by different materials.
• Fibre optics use total internal reflection of visible light or infrared to transmit data.
• In exam answers, always explain why a wave is suitable by linking its properties to the application.

---

Worked Examples — Matching Wave to Use

AQA rarely asks bare "which wave does what?" questions. Instead you will be given a scenario and asked which EM wave is suitable and why. These worked answers model the reasoning.

Worked Example 1 — Communicating with a satellite

A telecommunications company needs to send a signal up to a geostationary satellite 36 000 km above the Earth.

• Choice: microwaves.
• Why: microwaves pass through the Earth's atmosphere (including clouds and ionosphere) without being strongly absorbed, making them suitable for satellite communication.