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Radio waves
Beginner
Used for broadcasting and communication.
Wavelengths from mm to km; used for broadcasting, mobile phones and Wi-Fi. AM waves can bounce off the ionosphere.
FM at about 100 MHz has λ = 3 m.
Antenna length ~λ/2 or λ/4.
In more detail
Radio waves are electromagnetic waves with frequencies from about 3 kHz to 300 GHz, used for broadcasting, communication and navigation. Their long wavelengths can travel around obstacles and through the atmosphere.
Real-world uses
- AM and FM radio broadcast information on radio waves.
- Mobile phones and Wi-Fi use radio waves.
- Radio stations broadcast programmes using radio waves, which can travel long distances and around obstacles.
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Frequently asked questions
Why does AM travel further than FM?
AM uses lower frequencies that reflect off the ionosphere and diffract more.
What is the typical FM band?
88 to 108 MHz in many countries.
Why can radio waves go round hills?
Their long wavelengths diffract around obstacles more than short waves do.
Related topics in AC Circuits & EM Waves
Intensity of EM wave · Radiation pressure · EM spectrum · Microwaves · Infrared · Visible light