45.The source of Energy
A summary of the physical and chemical nature of life must begin, not on the Earth, but in the Sun; in fact, at the Suns very center. It is here that is to be found the source of the energy that the Sun constantly pours out into space as light and heat. This energy is librated at the center of the Sun as billions upon billions of nuclei of hydrogen atoms collide with each other and fuse together to form nuclei of helium, and in doing so, release some of the energy that is stored in the nuclei of atoms. The output of light and heat of the Sun requires that some 600 million tons of hydrogen be converted into helium in the Sun every second. This the Sun has been doing for several thousands of millions of year.
The nuclear energy is released at the Suns center as high-energy gamma radiation, a form of electromagnetic radiation like light and radio waves, only of very much shorter wavelength. This gamma radiation is absorbed by atoms inside the Sun to be reemitted at slightly longer wavelengths. This radiation , in its turn is absorbed and reemitted. As the energy filters through the layers of the solar interior, it passes through the X-ray part of the spectrum eventually becoming light. At this stage, it has reached what we call the solar surface, and can escape into space without being absorbed further by solar atoms. A very small fraction of the Suns light and heat is emitted in such directions that after passing unhindered through interplanetary space, it hits the Earth.
英语自学者的雅思听力练习方法
雅思听力精听泛听练习法:逆向法
雅思听力训练中应注意的几个问题
雅思听力考试如何消除紧张感(英)
雅思听力词汇整理
雅思听力做题小贴士
雅思听力材料:达芬奇-最后的晚餐(BBC纪录片)
雅思听力备考的五大禁忌
雅思(IELTS)听力考试的测试要点
趣谈:人在海外也离不了雅思听力
雅思听力场景词汇:图书馆场景
雅思听力外围突击学习法(下)
雅思听力课程笔记(补充)
雅思听力老师的备考建议
雅思听力笔记及考试要点
雅思听力训练的四个阶段及训练方法
雅思听力材料:德加-14岁的小舞女(BBC纪录片)
雅思听力外围突击学习法(上)
雅思听力训练中的四个注意事项
专家指导提高雅思听力水平的方法
雅思听力场景词汇:看病场景
雅思听力材料:毕加索-亚维农的姑娘(BBC纪录片)
雅思听力题型解题指南:Maps
雅思听力实用技巧:判断正误题
雅思(IELTS)听力考试的应试技巧
雅思听力场景词汇:教育场景
雅思听力考试的间歇时间如何利用?
雅思听力高分炼成法(热身阶段)
雅思听力题型解题指南:Checking
雅思听力材料:爱德华.蒙克-呐喊(BBC纪录片)
不限 |
英语教案 |
英语课件 |
英语试题 |
不限 |
不限 |
上册 |
下册 |
不限 |