Each case of communicable disease is the result of an orderly progression in. a series of events. This series of events may be described as a three-link chain, each. link representing a factor essential to the transmission of disease. These links (figure 1-1) are: (1) The source of the disease (reservoir) (2) The means by which the disease may be transmitted (mode of.
Radio Waves. Radio waves are a type of electromagnetic (EM) radiation with wavelengths in the electromagnetic spectrum longer than infrared light . They have have frequencies from 300 GHz to as low as 3 kHz, and corresponding wavelengths from 1 millimeter to 100 kilometers. Like all other electromagnetic waves, radio waves travel at the speed of light. Naturally occurring radio waves are made by lightning or by astronomical objects.
Waves are generally divided up into two types of wave - longitudinal and transverse. Longitudinal waves are waves where the displacement of the particles is parallel to the direction of travel of the wave (the vibrations are along the direction of the travel of the wave). The example of this is sound waves, where there are compressions and rarefactions in the air that cause the sound to be transmitted.