The Fascinating World of Crystals
Just what are crystals? A crystal is an organized grouping of atoms, or molecules. Each crystal has different properties and shapes. For example, sugar crystals are oblong and slanted at the ends; salt crystals are cubic. Some elements can make more than one crystalline form. Carbon, as graphite, will conduct electricity, act as a lubricant between moving parts, be used as a writing tool (a pencil) and strengthen of steel. As diamond, carbon is used as an industrial cutting tool and as a gemstone in jewelry. Crystals can be used in many ways. Diamonds, rubies, sapphires, and emeralds have been the showiest use of crystals for thousands of years. They were highly valued due to their beauty and relative small amounts that exist in nature. In recent years chemists have been working on methods of creating some of these crystals in the laboratory with a lot of success. Each different crystal vibrates at a specific frequency when an electric current is passed through it. The original radios were created using vibrating crystals to create the frequency to transmit signals. As radio technology improved, radio transmitters had several different crystals to allow transmission on different frequencies. Modern radios have large number of different frequencies used by radio stations. Vibrating crystals can be used for time keeping. A quartz clock uses the vibration of a quartz crystal to measure time. When the crystal has an electric current passed through it, the crystal will vibrate at 60 hertz (60 times per second). Дайте відповіді на запитання. 1. What shape has a salt crystal? а) star; b) cubic; b) pyramid. 2. Some crystaline form of carbon is used as a ___. а) lubricant between moving parts; b) rocket fuel; в) food additive. 3. In the radio, vibrating crystals are used ___. а) to switch between channels; b) to transmit signals; в) to receive signals. 23.4. Граматика. Функції дієслів to be, to have
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