单选题The distance from which a certain light is visible is directly proportional to the wattage of the light bulb. If the light is visible from 16 meters when a 40 watt bulb is used, from what distance is the light visible when a 75 watt bulb is used?A 30 metersB 35 metersC 51 metersD 89 metersE 91 meters

考题 Have you ever served the auxiliary engine to combustion heavy oil? What should be borne in mind when transferring oil; from heavy oil to light oil?

查看答案

考题 Edison invented the light bulb many years ago（改为被动语态）The light bulb__________ __________by Edison many years ago．

查看答案

考题 A head on situation shall be deemed to exist at night when a power-driven vessel sees another power-driven vessel ahead and ______.A.one sidelight and the masthead light are visibleB.the vessels will pass closer than half a mileC.both vessels sound one prolonged blastD.both sidelights and masthead light(s) are visible

查看答案

考题 The symbol which appears beside a light on a chart reads Gp Fl R (2) 10 sec 160 ft 19M. Which characteristic describes the light?A.It is visible 10 milesB.Its distinguishing number is 19MC.It has a radar reflectorD.None of the above

查看答案

考题 When making landfall at night，the light from a powerful lighthouse may sometimes be seen before the lantern breaks the horizon．This light is called the ______．A.diffusionB.backscatterC.loomD.elevation

查看答案

考题共用题干 Electromagnetic Energy1 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 kinds 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 much energy that they travel 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'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.Infrared radiation can produce heat______. A:when it is absorbed by matterB:when it is cloudyC:because they can pass through solid objectsD:when the sunrays are fierce.E:when a change in the nucleus of an atom takes placeF:when electron rearrangement takes place

查看答案

考题共用题干 Electromagnetic Energy1 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 cloudyday 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.Yet we can use energy from the sun because elec-tromagnetic 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 electro- 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.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 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-tncity.It is also being used to operate engines in large ships.Scientists continue to seek new and better methods of obtaining and using energy.When electron rearrangement takes place,_____________.A:electromagnetic energyB:electromagnetic energy travels through spaceC:came from the sunD:when a change in the nucleus of an atom takes placeE:when the sunrays are fierceF:chemical energy is generated

查看答案

考题共用题干 Electromagnetic Energy1 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 kinds 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 much energy that they travel 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'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.Paragraph 4______A:Nuclear Reactions as the Lasting Source of the Sun's EnergyB:The Most Important Source of EnergyC:Types of Electromagnetic EnergyD:The Machines Used for Energy GenerationE:Seeking New Sources of EnergyF:The Use of Ultravio1et Radiation in Medicine

查看答案

考题共用题干 Electromagnetic Energy1 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 kinds 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 much energy that they travel 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'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.X-rays and gamma rays can be used to detect and treat cancer______.A:when it is absorbed by matterB:when it is cloudyC:because they can pass through solid objectsD:when the sunrays are fierce.E:when a change in the nucleus of an atom takes placeF:when electron rearrangement takes place

查看答案

考题共用题干 Electromagnetic Energy1 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 cloudyday 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.Yet we can use energy from the sun because elec-tromagnetic 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 electro- 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.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 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-tncity.It is also being used to operate engines in large ships.Scientists continue to seek new and better methods of obtaining and using energy.Visible light that produces warmth is an example of______________.A:electromagnetic energyB:electromagnetic energy travels through spaceC:came from the sunD:when a change in the nucleus of an atom takes placeE:when the sunrays are fierceF:chemical energy is generated

查看答案

考题共用题干 Electromagnetic Energy1 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 cloudyday 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.Yet we can use energy from the sun because elec-tromagnetic 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 electro- 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.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 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-tncity.It is also being used to operate engines in large ships.Scientists continue to seek new and better methods of obtaining and using energy.We can use energy from the sun because_____________.A:electromagnetic energyB:electromagnetic energy travels through spaceC:came from the sunD:when a change in the nucleus of an atom takes placeE:when the sunrays are fierceF:chemical energy is generated

查看答案

考题共用题干 Learn about Light1 .Ancient civilizations were amazed by the existence of light for thousands of years. The Greek philosophers believed that light was made up of countless,tiny particles that enter the human eye and create what we call vision. However,Empedocles and a Dutch scientist named Christian Huygens believed that light was like a wave. According to them,light spread out and travelled like a straight line. This theory was accepted during the 19th century.2 .In 1905,Albert Einstein published a research paper in which he explained what is re-ferred to as the photoelectric effect. This theory explains that particles make up light.The particles Einstein was referring to are weightless bundles（束）of electromagnetic（电磁）energy called photons（光子）.Today,scientists agree that light has a dual（二重）nature一it is part particle and part wave. It is a form of energy that allows us to see things around us.3 .Things that give off light are known as sources of light. During the day,the primary source of light is the sun. Other sources of light include stars,flames,flashlights,street lamps and glowing gases in glass tube.4 .When we draw the way light travels we always use straight lines. This is because nor-mally light rays travel in a straight line. However,there are some instances that can change the path and even the nature of light. They are reflection,absorption,interference（干扰）, etc.5 .Physicists have attempted to measure the speed of light since the early times. In 1849, Hippolyte Fizeau conducted an experiment by directing a beam of light to a mirror located kilometers away and placed a rotating cogwheel（旋转齿轮）between the beam and the mirror. From the rate of rotation of the wheel,number of wheel's teeth and distance of the mirror,he was able to calculate that the speed of light is 313 million meters per second. In a vacuum（真空）,however,the speed of light is 299,792,458 meters per second. This is about a million times faster than the speed of an airplane.Paragraph 3______A: How Is the Nature of Light Explained Today?B: What Are Sources of Light?C: How Did Physicists Measure the Speed of Light?D: How Does Light Travel?E: How Did People Think of Light Years Ago?F: What Causes a Shadow?

查看答案

考题共用题干 Learn about Light1 .Ancient civilizations were amazed by the existence of light for thousands of years. The Greek philosophers believed that light was made up of countless,tiny particles that enter the human eye and create what we call vision. However,Empedocles and a Dutch scientist named Christian Huygens believed that light was like a wave. According to them,light spread out and travelled like a straight line. This theory was accepted during the 19th century.2 .In 1905,Albert Einstein published a research paper in which he explained what is re-ferred to as the photoelectric effect. This theory explains that particles make up light.The particles Einstein was referring to are weightless bundles（束）of electromagnetic（电磁）energy called photons（光子）.Today,scientists agree that light has a dual（二重）nature一it is part particle and part wave. It is a form of energy that allows us to see things around us.3 .Things that give off light are known as sources of light. During the day,the primary source of light is the sun. Other sources of light include stars,flames,flashlights,street lamps and glowing gases in glass tube.4 .When we draw the way light travels we always use straight lines. This is because nor-mally light rays travel in a straight line. However,there are some instances that can change the path and even the nature of light. They are reflection,absorption,interference（干扰）, etc.5 .Physicists have attempted to measure the speed of light since the early times. In 1849, Hippolyte Fizeau conducted an experiment by directing a beam of light to a mirror located kilometers away and placed a rotating cogwheel（旋转齿轮）between the beam and the mirror. From the rate of rotation of the wheel,number of wheel's teeth and distance of the mirror,he was able to calculate that the speed of light is 313 million meters per second. In a vacuum（真空）,however,the speed of light is 299,792,458 meters per second. This is about a million times faster than the speed of an airplane.Objects are visible to the human eye as light is______.A: sources of lightB: the speed of lightC: the path of lightD: a straight lineE: a beam of lightF: a form of energy

查看答案

考题共用题干第三篇Small but WiseOn December 14,NASA blasted a small but mighty telescope into space.The telescope is called WISE and is about as wide around as a trashcan.Don't let its small size fool you:WISE has a powerful digital camera,and it will be taking pictures of some of the wildest objects in the known universe,including asteroids,faint stars,blazing galaxies and giant clouds of dust where planets and stars are born."I'm very excited because we're going to be seeing parts of the universe that we haven't seen be- fore,"said Ned Wright,a scientist who directs the WISE project.Since arriving in space,the WISE telescope has been circling the Earth,held by gravity in a polar orbit (this means it crosses close to the north and south poles with each lap).Its camera is pointed outward,awayfrom the Earth,and WISE will snap a picture of a different part of the sky every 11 minutes.After six months it will have taken pictures across the entire sky.The pictures taken by WISE won't be like everyday digital photographs,however. WISE stands for "Wide-field Infrared Survey Explorer".As its name suggests,the WISE camera takes pictures of features that give off infrared radiation.Radiation is energy that travels as a wave.Visible light,including the familiar spectrum of light that be- comes visible in a rainbow,is an example of radiation.When an ordinary digital camera takes a picture of a tree,for example,it receives the waves of visible light that are reflected off the tree.When these waves enter the camera through the lens,they're processed by the camera,which then puts the image together.Waves of infrared radiation are longer than waves of visible light,so ordinary digital cameras don't see them,and neither do the eyes of human beings.Although invisible to the eye,longer infrared radiation can be detected as warmth by the skin.That's a key idea to why WISE will be able to see things other telescopes can't. Not everything in the universe shows up in visible light.Asteroids,for example, are giant rocks that float through space一but they absorb most of the light that reaches them.They don't reflect light,so they're difficult to see.But they do give off infrared radiation,so an infrared telescope like WISE will be able to produce images of them.During its mission WISE will take pictures of hundreds of thousands of asteroids.Brown dwarfs are another kind of deep-space objects that will show up in WISE's pictures.These ob- jects are "failed" stars一which means they are not massive enough to jump-start the same kind of reactions that power stars such as the sun.Instead,brown dwarfs simply shrink and cool down.They're so dim that they're almost impossible to see with visible light,but in the infrared spectrum they glow.It is true that infrared radiation_________.A:is not detectable to humansB:looks brighter than visible lightC:is visible light reflected off an objectD:has longer waves than those of visible light

查看答案

考题共用题干 Electromagnetic Energy1 White light seems to be a combination of all colors.The energy that comes from a source of light isnot 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 hiddencracks 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 bettermethods of obtaining and using energy.When electron rearrangement takes place_______________.A:electromagnetic energyB:electromagnetic energy travels through spaceC:came from the sunD:when a change in the nucleus of an atom takes placeE:whlen the sunrays are fierce F:chemical energy is generated

查看答案

考题共用题干 Electromagnetic Energy1 White light seems to be a combination of all colors.The energy that comes from a source of light isnot 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 hiddencracks 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 bettermethods of obtaining and using energy.Visible light that produces warmth is an example of _______________.A:electromagnetic energyB:electromagnetic energy travels through spaceC:came from the sunD:when a change in the nucleus of an atom takes placeE:whlen the sunrays are fierce F:chemical energy is generated

查看答案

考题共用题干 Learn About Light1 Ancient civilizations were amazed by the existence of light for thousands of years?The Greek philoso- phrrs believed that light was made up of countless,tiny particles that enter the human eye and create what we call vision.However,Empedocles and a Dutch scientist named Christian Huygens believed that light wag like a wave.According to them,light spread out and travelled like a straight line.This theory was acceptedduring the 19th century.2 In 1905,Albert Einstein published a research paper in which he explained what is referred to as the photoelectric effect.This theory explains that particles make up light.The particles Einstein was referring to are weightless bundles（束）of electromagnetic（电磁）energy called photons（光子）.Today,scientists agree that light has a dual（二重）nature一it is part particle and part wave. It is a form of energy that allows us tosee things around us.3 Things that give off light are known as sources of light.During the day,the primary source of light is the sun.Other sources of light include stars,flames,flashllights,street lamps and glowing gases in glass tube.4 When we draw the way light travels we always use straight lines.This is because normally light rays travel in a straight line.However,there are some instances that can change the path and even the nature of light. They are reflection,absorption,interference（干扰）,etc.5 Physicists have attempted to measure the speed of light since the early times.In 1849,Hippolyte Fizeau conducted an experiment by directing a beam of light to a mirror located kilometers away and placed a rotating cogwheel（旋转齿轮）between the beam and the mirror. From the rate of rotation of the wheel, number of wheel'S teeth and distance of the mirror,he was able to calculate that the speed of light is 313 million meters per second.In a vacuum（真空）,however,the speed of light is 299,792,458 meters per second.This is about a million times faster than the speed of an airplane.Objects are visible to the human eye as light is_______. A:sources of lightB:the speed of light C:the path of lightD:a straight lineE:a beam of lightF:a form of energy

查看答案

考题单选题All of the following information concerning lighted aids to navigation may be read directly from the Light List EXCEPT the（）.A locationB height of light above waterC luminous rangeD light characteristics

查看答案

考题单选题Some lights used as aids to marine navigation have a red sector to indicate a danger area. The limits of a colored sector of a light are listed in the Light List in which of the following manners?（）A Geographical positions outlining the area of the sectorB True bearings as observed from the ship toward the lightC An outline of the area of the sectorD True bearings as observed from the light toward the ship

查看答案

考题单选题An alternating light（）.A shows a light with varying lengths of the lighted periodB shows a light that changes colorC marks an alternate lesser-used channelD is used as a replacement for another light

查看答案

考题单选题The color of the exhaust from a diesel engine should be （）A clearB hazy light brownC hazy light blueD hazy light grey

查看答案

考题单选题If several fixed navigational lights are visible at the same time，each one may be positively identified by checking all of the following EXCEPT what against the Light List?（）A RhythmB PeriodC IntensityD Color

查看答案

考题单选题The minimum length of a boat painter for a lifeboat in ocean service is（）.A 60 fathomsB the distance from the main deck to the light waterlineC twice the distance from the main deck to the light waterline or 50 feet whichever is greaterD two times the distance from the boat deck to the light waterline or 50 feet whichever is greater

查看答案

考题单选题You have berthed in a area with other tank vessels. What signal is displayed by a vessel to indicate it is transferring flammable or combustible liquid cargo?（）.A A flashing yellow lightB A red light visible all around the horizonC A green light visible all around the horizonD An illuminated red and yellow caution flag

查看答案

考题单选题When making landfall at night，you can determine if a light is a major light or an offshore buoy by（）.A the intensity of the lightB checking the period and characteristics against the Light ListC the color，because the buoy will have only a red or a green lightD Any of the above can be used to identify the light

查看答案

考题单选题A head on situation shall be deemed to exist at night when a power-driven vessel sees another power-driven vessel ahead and （）.A one sidelight and the masthead light are visibleB the vessels will pass closer than half a mileC both vessels sound one prolonged blastD both sidelights and masthead light(s) are visible

查看答案

考题单选题A flashing light is a light that（）.A flashes at regular intervals at a frequency of 120 flashes or more per minuteB is yellow in colorC is visible over an arc of the horizon of not less than 180°nor more than 225°D All of the above

查看答案

网友您好， 请在下方输入框内输入要搜索的题目：

网友您好，请在下方输入框内输入要搜索的题目：