tailieunhanh - Acing The Gre phần 6

Tham khảo tài liệu 'acing the gre phần 6', ngoại ngữ, anh ngữ phổ thông phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | PHYSICAL SCIENCE Each kind of atom or molecule can gain or lose energy only in particular discrete amounts. When an atom gains energy light at the wavelength associated with that energy is absorbed. When an atom loses energy light at the wavelength associated with that energy is emitted. These wavelengths can be used to identify elements. Nuclear Reactions In a nuclear reaction energy can be converted to matter and matter can be converted to energy. In such processes energy and matter are conserved according to Einstein s formula E mc2 where E is the energy m is the mass matter and c is the speed of light. A nuclear reaction is different from a chemical reaction because in a nuclear reaction the particles in nuclei protons and neutrons interact whereas in a chemical reaction electrons are lost or gained by an atom. Two types of nuclear reactions are fusion and fission. Fusion is a nuclear process in which two light nuclei combine to form one heavier nucleus. A fusion reaction releases an amount of energy more than a million times greater than the energy released in a typical chemical reaction. This gain in energy is accompanied by a loss of mass. The sum of the masses of the two light nuclei is lower than the mass of the heavier nucleus produced. Nuclear fusion reactions are responsible for the energy output of the sun. Fission is a nuclear process in which a heavy nucleus splits into two lighter nuclei. Fission reaction was used in the first atomic bomb and is still used in nuclear power plants. Fission like fusion liberates a great amount of energy. The price for this energy is a loss in mass. A heavy nucleus that splits is heavier than the sum of the masses of the lighter nuclei that result. Key Concepts This chapter gave you a crash course in the basics of physical science. Here are the most important concepts to remember ậ All matter is composed of tiny particles called atoms. ậ Atoms combine with other atoms to form molecules. ậ In a chemical reaction atoms .