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 fails 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'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. A. Nuclear reactions as the lasting source of the sun's
energy B. The most important source of energy
C. Types of electromagnetic energy D. The machines used for
energy generation E. Seeking new sources of energy
F. The use of ultraviolet radiation in medicine
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Paragraph 3 ______.
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Paragraph 4 ______.
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Paragraph 5 ______.
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Paragraph 6 ______.
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A. when it is absorbed by matter
B. when it is cloudy
C. because they can pass through solid objects
D. when the sunrays are fierce
E. when a change in the nucleus of an atom takes place
F. when electron rearrangement takes place
One can get a sunburn even ______.
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Infrared radiation can produce heat ______.
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X-rays and gamma rays can be used to detect and treat cancer ______.