Radio astronomers conduct observations in the microwave region, but due to attenuation by the atmosphere, most of these studies are done using high-altitude balloons or satellites. This panoramic view of Chajnantor plateau in Chile shows the antennas of the Atacama Large Millimeter/submillimeter Array (ALMA) against a breathtaking starry night sky. Microwave heating systems are also used in a number of industrial applications, including food, chemical and materials processing in both batch and continuous operations. The first microwave ovens were quite large and expensive, but they have since become so affordable that they are common in homes worldwide. Suddenly he noticed that a candy bar in his pocket had begun to melt." Further investigation led him to make the first batch of microwave popcorn as well as the first exploding egg.
Spencer stopped in front of a magnetron, the power tube that drives a radar set. Spencer, an electronics genius and war hero, was touring one of his laboratories at the Raytheon Company. In his book, " They All Laughed.: From the Light Bulbs to Lasers: The Fascinating Stories Behind the Great Inventions That Have Changed Our Lives (opens in new tab)" (HarperCollins, 1992), author Ira Flatow recounts the story of the invention of the microwave oven: "Shortly after World War II, Percy L. The discovery of this phenomenon was purely accidental. Microwave ovens are possible because microwaves can be used to transmit thermal energy. One of the most common uses of microwaves is to heat food quickly. Many of these observations are conducted by satellites looking either back at the Earth or out into space. In passive sensing, natural sources of microwaves are observed and analyzed. These applications are called active sensing, because microwaves are transmitted, and the reflected signals are received and analyzed. By measuring this frequency shift, the speed of an object toward or away from the antenna can be determined.Ĭommon applications of this principle include simple motion detectors, radar guns for speed-limit enforcement, radar altimeters and weather radar that can track the 3D motion of water droplets in the atmosphere. Conversely, return waves from objects moving away are elongated and have a longer wavelength and lower frequency. When an object is approaching the antenna, the returning microwaves are compressed and thus have a shorter wavelength and higher frequency.
Robert Mayanovic, a professor of physics at Missouri State University, said that Doppler radar, which often employs microwaves, is used for air-traffic control and vehicular speed-limit enforcement. Then, as it recedes into the distance, the siren seems to lower in pitch. An example of the Doppler effect can be demonstrated by an approaching ambulance: As it nears, the sound of the siren seems to rise in pitch, until it wails by. Radar has found many other uses, some of which exploit the Doppler effect. Over the course of the war, radar was improved and refined, and it has since become an essential element of national defense and civilian air-traffic control. However, because the system had been in operation for only two weeks, it was considered unreliable, and the warning was ignored. According to the state of Hawaii's website, the station actually detected the first wave of Japanese aircraft on their way to attack Pearl Harbor when the planes were 132 miles (212 kilometers) out. A little-known historical fact is that an early radar installation was built atop Kahuku Point on Oahu's northernmost tip.
0 kommentar(er)
