A signal containing information on the brightness levels of different portions of an image along with information on line and frame synchronization. In the case of satellite signals, the video information is transmitted in the form of an AM modulated subcarrier . Visible That part of the electromagnetic spectrum to which the human eye is sensitive, between about 0.4 and 0.7 micrometers. See spectrum . Volcano A naturally occurring vent or fissure at the Earth's surface through which erupt molten, solid, and gaseous materials.
Volcanic eruptions inject large quantities of dust, gas, and aerosols into the atmosphere.
A major component of volcanic clouds is sulfur dioxide, a strong absorber of ultraviolet radiation. Chemical interactions between sulfur dioxide and water cause sulfuric acid aerosols which can scatter some of the incident solar radiation back to space, thus causing a global cooling effect. The unit of electromotive force , or difference of potential, which will cause a current of one ampere to flow through a resistance of one ohm .