What type of waves are primarily used for communication and have the longest wavelengths?

Radio waves are primarily used for communication due to their unique properties, including their long wavelengths. These wavelengths can range from about a millimeter to thousands of kilometers, which allows them to travel long distances and penetrate various materials effectively. This characteristic makes radio waves particularly suitable for applications such as broadcasting television and radio signals, as well as in telecommunications and satellite communication.

In addition to their long wavelengths, radio waves are effective at carrying information over large distances because they can be modulated easily. This means that different types of information, such as voice and data, can be encoded into a radio wave without significant loss of quality over the transmission distance.

The other types of waves listed have shorter wavelengths and different properties that make them less suitable for communication. Microwaves, for instance, are used in certain types of communication and cooking due to their ability to excite water molecules. Infrared waves are primarily associated with thermal radiation, while gamma rays, at the other end of the spectrum, have very short wavelengths and are typically associated with nuclear reactions and not used for communication due to their high energy and penetrating power.