section_path: Technology
section_name: Technology
paragraph_text: Technology
  
  Radio waves are radiated by electric charges undergoing acceleration. They are generated artificially by time-varying electric currents, consisting of electrons flowing back and forth in a metal conductor called an antenna.
  
  As they travel farther from the transmitting antenna, radio waves spread out so their signal strength (intensity in watts per square meter) decreases (see Inverse-square law), so radio transmissions can only be received within a limited range of the transmitter, the distance depending on the transmitter power, the antenna radiation pattern, receiver sensitivity, background noise level, and presence of obstructions between transmitter and receiver. An omnidirectional antenna transmits or receives radio waves in all directions, while a directional antenna transmits radio waves in a beam in a particular direction, or receives waves from only one direction.
  
  Radio waves travel at the speed of light in vacuum.
  
  The other types of electromagnetic waves besides radio waves, infrared, visible light, ultraviolet, X-rays and gamma rays, can also carry information and be used for communication. The wide use of radio waves for telecommunication is mainly due to their desirable propagation properties stemming from their large wavelength.