共用题干

共用题干
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 away from the earth.Yct we can use energy from die sun because elec-
tromagnetic energy travels through space.
3 Many other kinds of energy are also types of electromagnetic energy.Radio,television,and radar signais
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.Wayes of infrared and visible light
have more energy than waves of radio,television,or radar. Ultraviolet rays（紫外线）and X-rays are eleetro-
magnetic 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 much 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．入bout 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 chemi-
cal 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 elec-
tricity.It is also being used to operate engines in large ships.Scientists continue to seek new and better
methods of obtaining and using energy.

The energy stored in coal_______________.
A:electromagnetic energy
B:electromagnetic energy travels through space
C:came from the sun
D:when a change in the nucleus of an atom takes place
E:whlen the sunrays are fierce
F:chemical energy is generated