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.
Different types of seismic waves include: Surface waves: Seismic waves that travel along the Earthâs surface. Body waves: Seismic waves that travel through the Earthâs interior. There are two types: Primary waves (P waves): Body waves that compress and expand rock in the direction the waves travel (like a slinky). Secondary waves (S waves): Body waves that shake material at right angles to the direction the waves travel (like shaking a rope). Solid rock transmits S waves, but gases and liquids do not.