Know that many important systems of communications rely on electromagnetic radiation including: (a) mobile phones (cell phones) and wireless internet use microwaves because microwaves can penetrate some walls and only require a short aerial for trans
Electromagnetic (EM) radiation spans a wide range of frequencies and wavelengths. Different parts of the spectrum are exploited for various communication technologies because of their distinct propagation characteristics.
Key Communication Systems and Their EM Regions
Mobile phones (cell phones) and wireless internet – use microwaves (≈ 1 GHz to 30 GHz). Microwaves can penetrate some walls and require only a short aerial (antenna) for transmission and reception.
Bluetooth – uses radio waves (≈ 2.4 GHz ISM band). Radio waves readily pass through walls, though the signal strength is reduced.
Optical fibres (cable television & high‑speed broadband) – employ visible light or infrared (≈ 400 THz to 400 THz for visible, 300 THz–400 THz for near‑infrared). Glass is highly transparent to these wavelengths, allowing low‑loss transmission over long distances.
Why These Parts of the Spectrum Are Chosen
Microwaves
Wavelengths (≈ 1 cm to 30 cm) are short enough to allow compact antennas.
They can diffract around obstacles and penetrate non‑metallic walls, providing reliable indoor coverage.
Longer wavelengths (≈ 10 cm to 1 m) easily pass through walls and other non‑conductive materials.
Low power consumption makes them ideal for short‑range, battery‑powered devices like Bluetooth headsets.
Limited bandwidth compared with microwaves, suitable for low‑rate data exchange.
Visible/Infrared light in fibres
Glass has a very low absorption coefficient for these wavelengths, resulting in attenuation of only a few dB/km.
Light can be guided by total internal reflection, keeping the signal confined within the core.
Extremely high frequencies give enormous bandwidth (up to several THz), supporting gigabit‑per‑second data rates.
Comparison of Communication Systems
System
EM Region
Typical Frequency Range
Wavelength Range
Key Advantages
Limitations
Mobile phones / Wi‑Fi
Microwave
1 GHz – 30 GHz
1 cm – 30 cm
Compact antennas; good indoor penetration; high data rates
Signal attenuation by metal objects; line‑of‑sight not always required but performance degrades with distance
Bluetooth
Radio wave (ISM band)
2.4 GHz (± 0.1 GHz)
≈ 12.5 cm
Low power; easy to integrate; works through walls
Limited range (≈ 10 m); lower bandwidth than Wi‑Fi
Optical fibre (cable TV, broadband)
Visible / Infrared light
≈ 200 THz – 400 THz
≈ 0.75 µm – 1.5 µm (in fibre core)
Very low loss; huge bandwidth; immune to electromagnetic interference
Requires physical cable; bending losses if radius too small; expensive installation
Fundamental Relationship
The speed of an electromagnetic wave in vacuum is given by
\$c = \lambda f\$
where c = \$3.0 \times 10^{8}\,\text{m s}^{-1}\$, λ is the wavelength, and f is the frequency. This relation explains why higher‑frequency (shorter‑wavelength) waves such as microwaves and light can carry more information per unit time.
Suggested diagram: A schematic showing a mobile phone, a Bluetooth headset, and an optical fibre cable, each labelled with its corresponding part of the electromagnetic spectrum.