Describe typical uses of the different regions of the electromagnetic spectrum including: (a) radio waves; radio and television transmissions, astronomy, radio frequency identification (RFID) (b) microwaves; satellite television, mobile phones (cell

3.3 Electromagnetic Spectrum

The electromagnetic (EM) spectrum covers a continuous range of wavelengths and frequencies. Different regions are exploited for a variety of practical applications. The table below summarises the main regions, their typical wavelength ranges and common uses.

Detailed Uses by Region

Radio Waves

Radio waves have the longest wavelengths in the EM spectrum. Their low frequency allows them to travel long distances and penetrate obstacles, making them ideal for broadcasting and communication.

• Radio and television transmissions: AM, FM, DAB and T \cdot signals are transmitted using specific frequency bands.
• Astronomy: Radio telescopes detect natural radio emissions from celestial objects such as pulsars and gas clouds.
• RFID: Small tags use radio waves to exchange data with readers for inventory control and contactless payment.

Microwaves

Microwaves occupy the region between radio waves and infrared. Their ability to be directed in narrow beams and to be reflected by metallic surfaces is exploited in communications and heating.

• Satellite television: Signals are beamed from satellites to dish antennas using microwave frequencies.
• Mobile phones: Cellular networks allocate microwave bands (e.g., 900 MHz, 1800 MHz) for voice and data.
• Microwave ovens: Water molecules absorb microwaves (≈2.45 GHz), converting electromagnetic energy into heat.

Infrared (IR)

Infrared radiation is associated with thermal energy. Many everyday devices either emit or detect IR.

• Electric grills: IR heating elements provide rapid, even heating.
• Remote controllers: IR LEDs transmit coded signals to televisions and other appliances.
• Thermal imaging: Cameras detect IR emitted by warm objects, useful for night vision and building inspections.
• Optical fibres: IR light (typically 1.3 µm or 1.55 µm) travels with low loss through glass fibres for high‑speed data transmission.

Visible Light

Visible light is the narrow band of the spectrum that the human eye can detect.

• Vision: Enables sight for humans and many animals.
• Photography: Cameras capture visible photons to produce images.
• Illumination: Light bulbs, LEDs and lasers provide artificial lighting.

Ultraviolet (UV)

U \cdot radiation has higher energy than visible light and can cause chemical changes.

• Security marking: UV‑fluorescent inks are invisible under normal light but reveal patterns under U \cdot lamps.
• Fake bank‑note detection: U \cdot features embedded in genuine notes become visible under U \cdot illumination.
• Sterilising water: U \cdot lamps destroy microorganisms by damaging their DNA.

X‑rays

X‑rays have enough energy to penetrate soft tissue but are absorbed by denser materials such as bone.

• Medical scanning: Radiographs and computed tomography (CT) produce internal images of the body.
• Security scanners: Airport baggage scanners use X‑rays to reveal concealed objects.

Gamma Rays

Gamma rays are the highest‑energy photons, emitted from nuclear transitions and certain astronomical sources.

• Sterilising food and medical equipment: Gamma irradiation kills bacteria and spores without raising temperature.
• Cancer detection and treatment: Positron emission tomography (PET) uses gamma photons for imaging; radiotherapy employs gamma rays to destroy malignant cells.