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Electromagnetic Energy
1. White light seems to be a combination of all colors. The energy that comes from a source of light is not limited to the kind of energy you can see. Heat is given off by a flame or an electric light. On a cloudy day it is possible to get a sunburn even though you feel cool. Visible light and the kind of energy that produce warmth and sunburn are examples of electromagnetic energy.
2. The sun is 93 million miles from the earth. Yet we can use energy from the sun because electromagnetic energy travels through space.
3. Many other kinds of energy are also types of electromagnetic energy. Radio, television, and radar signals travel from transmitters to receivers as low-energy electromagnetic waves. Infrared (红外线的 ) radiation is an electromagnetic wave. When it is absorbed by matter, heat is produced. Waves of infrared and visible light have more energy than waves of radio, television, or radar. Ultraviolet rays (紫外线 ) and X-rays are electromagnetic waves with even greater amounts of energy. Infrared radiation is used in cooking food and heating buildings. Sunlight and electric lights are part of our requirements for normal living. Ultraviolet radiation is useful in killing certain disease organisms. X-rays and gamma rays have so mush energy that they travel right through solid objects. They can be used to detect and treat cancer. X-rays are used in industry to find hidden cracks in metal, and in medicine to reveal broken bones.
4. Usually we use electricity to generate electromagnetic energy. The source of most of our energy is the sun. Heat from the sun causes water to evaporate. When the water falls to the earth as rain, some of it is trapped behind dams and then used to operate electric generators. Other generators are powered by coal, but the energy stored in coal came from the sun, too.
5. Until recently, the source of the tremendous amount of energy given off by the sun was a puzzle. If the sun depended on chemical reactions, it would have used up all its energy long ago. Experiments with electromagnetic radiation led to the theory that mass can be converted into energy. About forty years after the theory was proposed, nuclear energy was harnessed (利用 ) by man. Chemical energy comes from electron (电子 ) rearrangement. Nuclear energy comes from a change in the nucleus of an atom. Compared with chemical reactions, nuclear reactions release millions of times more energy per pound of fuel. We now believe that the sun&39;s energy comes from the nuclear reactions in which hydrogen is changed into helium (氦 ) .
6. Nuclear energy is beginning to compete with coal as an economical source of power to generate electricity. It is also being used to operate engines in large ships. Scientists continue to seek new and better methods of obtaining and using energy.
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Coming Soon to a Theater Near YouI
What are special effects？ Do you enjoy movies that use a lot of special effects？
Dinosaurs(恐龙)from the distant past! Space battles from the distant future! There has been a revolution in special effects，and it has transformed the movies we see．
The revolution began in the mid．1970s with George Lucas’s Star Wars，a film that stunned(使震惊)audiences．That revolution continues to the present，with dramatic changes in special-effects technology．The company behind these changes is Lucas’s Industrial Light＆Magic(ILM)．And the man behind the company is Dennis Muren，who has worked with Lucas since Star Wars．
Muren’s interest in special effects began very early．At the age of 6，he was photographing toy dinosaurs and spaceships．At 10，he had an 8-millimeter movie camera and was making these things move through stop-motion．(Stop-motion is a process in which objects are shot with a camera，moved slightly，shot again，and so on．When the shots are put together，the object appear to move．)
Talk to Muren and you’ll understand what ILM is all about：taking on new challenges．By 1989，Muren decided he had pushed the old technology as far as it would go．
He saw computer graphics(图像)(CG)technology as the wave of the future and took a year off to master it．
With CG technology，images can be scanned into a computer for processin9，for example，and many separate shots can be combined into a single image．CG technology has now reached the point，Muren says，where special effects can be used to do just about anything so that movies can tell stories better than ever before．The huge success of Jurassic Park and its sequel(续集)，The Lost Word，the stars of which were computer-generated dinosaurs，suggests that this may very well be true．
The special-effects revolution began in the mid-1980s with Star Wars． 查看材料
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