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单选题
The magnetic field is provided by electromagnets so arranged that adjacent poles have （）.
A
opposite polarity
B
the same polarity
C
negative polarity
D
positive polarity
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更多 “单选题The magnetic field is provided by electromagnets so arranged that adjacent poles have （）.A opposite polarityB the same polarityC negative polarityD positive polarity” 相关考题
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When placed in a magnetic field, which of the materials listed will maintain the highest permeability?( )A.GlassB.BakeliteC.Soft ironD.Aluminum
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The magnetic field is provided by electromagnets so arranged that adjacent poles have ___.A.opposite polarityB.the same polarityC.negative polarityD.positive polarity
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Permanent magnetism is caused by ______.A.operation of electrical equipment and generators on board shipB.the earth's magnetic field affecting the ship's hard iron during constructionC.the horizontal component of the earth's magnetic field acting on the horizontal soft ironD.the vertical component of the earth's magnetic field acting on the vertical soft iron
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If a magnetic compass is not affected by any magnetic field other than the Earth’s which statement is TRUE?______.A.Compass error and variation are equalB.Compass north will be true northC.Variation will equal deviationD.There will be no compass error
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共用题干
The Northern LightsThe Sun is stormy and has its own kind of weather It is so hot and active that even the Sun's gravity cannot hold its atmosphere in check!Energy flows away from the Sun toward the Earth in a stream of electrified particles that move at speeds around a million miles per hour. These particles are called plasma,and the stream of plasma coming from the Sun is called the solar wind. The more active the Sun,the stronger the solar wind.The solar wind constantly streams toward the Earth,but don't worry because a protective magnetic field surrounds our planet.The same magnetic field that makes your compass point north also steers the particles from the Sun to the north and south poles.The charged particles become trapped in magnetic belts around the Earth. When a large blast of solar wind crashes into the Earth's magnetic field,the magnetic field first gets squeezed and then the magnetic field lines break and reconnect.The breaking and reconnecting of the magnetic field lines can cause atomic particles called electrons trapped in the belts to fall into the Earth's atmosphere at the poles. As the electrons fall to the Earth,they collide with gas molecules in the atmosphere,creating flashes of light in the sky. Each atmospheric gas glows a different color. Oxygen and nitrogen glows red and green and nitrogen glows violet-purple. As these various colors glow and dance in the night sky,they create the Northern Lights and the Southern Lights.Watching auroras is fun and exciting,but normally you can only see them in places far north like Alaska and Canada. The movement of the aurora across the sky is usually slow enough to easily follow with your eyes but they can also pulsate,flicker,or even move like waves.During solar maximum,auroras are seen as far south as Florida,even Mexico!Auroras often seem to be very close to the ground,but the lowest aurora is still about 100 kilometers above the ground,a distance much higher than clouds are formed or airplanes can fly. A typical aurora band can be thousands of kilometers long,a few hundred kilometers high,but only a few hundred meters thick.We hope you are able to travel to far north places like the Arctic Circle and see the Northern Lights at least once during your lifetime. We know you will never forget it!Some scientists are worrying about the possible disappearance of the Earth's protective magnetic field in the future.A: RightB: WrongC: Not mentioned
考题
共用题干
The Northern LightsThe Sun is stormy and has its own kind of weather It is so hot and active that even the Sun's gravity cannot hold its atmosphere in check!Energy flows away from the Sun toward the Earth in a stream of electrified particles that move at speeds around a million miles per hour. These particles are called plasma,and the stream of plasma coming from the Sun is called the solar wind. The more active the Sun,the stronger the solar wind.The solar wind constantly streams toward the Earth,but don't worry because a protective magnetic field surrounds our planet.The same magnetic field that makes your compass point north also steers the particles from the Sun to the north and south poles.The charged particles become trapped in magnetic belts around the Earth. When a large blast of solar wind crashes into the Earth's magnetic field,the magnetic field first gets squeezed and then the magnetic field lines break and reconnect.The breaking and reconnecting of the magnetic field lines can cause atomic particles called electrons trapped in the belts to fall into the Earth's atmosphere at the poles. As the electrons fall to the Earth,they collide with gas molecules in the atmosphere,creating flashes of light in the sky. Each atmospheric gas glows a different color. Oxygen and nitrogen glows red and green and nitrogen glows violet-purple. As these various colors glow and dance in the night sky,they create the Northern Lights and the Southern Lights.Watching auroras is fun and exciting,but normally you can only see them in places far north like Alaska and Canada. The movement of the aurora across the sky is usually slow enough to easily follow with your eyes but they can also pulsate,flicker,or even move like waves.During solar maximum,auroras are seen as far south as Florida,even Mexico!Auroras often seem to be very close to the ground,but the lowest aurora is still about 100 kilometers above the ground,a distance much higher than clouds are formed or airplanes can fly. A typical aurora band can be thousands of kilometers long,a few hundred kilometers high,but only a few hundred meters thick.We hope you are able to travel to far north places like the Arctic Circle and see the Northern Lights at least once during your lifetime. We know you will never forget it!You cannot see the Northern Lights unless you are in Alaska or Canada.A: RightB: WrongC: Not mentioned
考题
共用题干
第一篇The Northern LightsThe sun is stormy and has its own kind of weather.It is so hot and active that even the Sun's gravity cannot hold its atmosphere in check!Energy flows away from the Sun toward the Earth in a stream of electrified particles that move at speeds around a million miles per hour.These particles are called plasma （等离子体）,and the stream of plasma coming from the Sun is called the solar wind.The more active the Sun,the stronger the solar wind.The solar wind constantly streams toward the Earth,but don't worry because a protective magnetic field surrounds our planet.The same magnetic field that makes your compass point north also steers the particles from the Sun to the north and south poles.The charged particles become trapped in magnetic belts around the Earth.When a large blast of solar wind crashes into the Earth's magnetic field,the magnetic field first gets squeezed and then the magnetic field lines break and reconnect.The breaking and reconnecting of the magnetic field lines can cause atomic particles called electrons trapped in the belts to fall into tile Earth's atmosphere at the poles.As the electrons fall to the Earth,they collide with gas molecules in the atmosphere,creating flashes of light in the sky.Each atmospheric gas glows a different color.Oxygen and nitrogen glows red and green arid nitrogen glows violet purple.As these various colors glow and dance in the night sky,they create the Northern Lights and the Southern Lights.Watching auroras（北极光）is fun and exciting, but normally you can only see them in places far north like Alaska and Canada.The movement of the aurora across the sky is usually slow enough to easily follow with your eyes but they can also pulsate（跳动）,flicker（闪烁）,or even move like waves.During solar maximum,5 auroras are seen as far south as Florida,even Mexico!Auroras often seem to be very close to the ground,but the lowest aurora is still about 100 kilometers above the ground,a distance much higher than clouds are formed or airplanes can fly.A typical aurora band can be thousands of kilometers long,a few hundred kilometers high,but only a few hundred meters thick.We hope you are able to travel to far north places like the Arctic Circle and see the Northern Lights at least once during your lifetime.We know you will never forget it!What happens when solar wind comes to the Earth?A:It is trapped in magnetic belts around the Earth.B:A protective magnetic field is formed at the same time.C:It destroys the protective magnetic field surrounding the Earth.D:It breaks magnetic field lines and does severe damage to the Earth.
考题
共用题干
第一篇The Northern LightsThe sun is stormy and has its own kind of weather.It is so hot and active that even the Sun's gravity cannot hold its atmosphere in check!Energy flows away from the Sun toward the Earth in a stream of electrified particles that move at speeds around a million miles per hour.These particles are called plasma （等离子体）,and the stream of plasma coming from the Sun is called the solar wind.The more active the Sun,the stronger the solar wind.The solar wind constantly streams toward the Earth,but don't worry because a protective magnetic field surrounds our planet.The same magnetic field that makes your compass point north also steers the particles from the Sun to the north and south poles.The charged particles become trapped in magnetic belts around the Earth.When a large blast of solar wind crashes into the Earth's magnetic field,the magnetic field first gets squeezed and then the magnetic field lines break and reconnect.The breaking and reconnecting of the magnetic field lines can cause atomic particles called electrons trapped in the belts to fall into tile Earth's atmosphere at the poles.As the electrons fall to the Earth,they collide with gas molecules in the atmosphere,creating flashes of light in the sky.Each atmospheric gas glows a different color.Oxygen and nitrogen glows red and green arid nitrogen glows violet purple.As these various colors glow and dance in the night sky,they create the Northern Lights and the Southern Lights.Watching auroras（北极光）is fun and exciting, but normally you can only see them in places far north like Alaska and Canada.The movement of the aurora across the sky is usually slow enough to easily follow with your eyes but they can also pulsate（跳动）,flicker（闪烁）,or even move like waves.During solar maximum,5 auroras are seen as far south as Florida,even Mexico!Auroras often seem to be very close to the ground,but the lowest aurora is still about 100 kilometers above the ground,a distance much higher than clouds are formed or airplanes can fly.A typical aurora band can be thousands of kilometers long,a few hundred kilometers high,but only a few hundred meters thick.We hope you are able to travel to far north places like the Arctic Circle and see the Northern Lights at least once during your lifetime.We know you will never forget it!The Northern Lights are created when_______.A:the magnetic field lines fail to reconnectB:the electrons falling to the Earth shine in different colorsC:atomic particles fall to the Earth and collide with atmospheric gas moleculesD:oxygen and nitrogen are separated from the atmospheric gases
考题
Which of the following statements is NOT true?（）AThe open field system provided a good opportunity to experiment.BThe open field system wasted land.CThe open field system was wasteful of labor and time.DThe open field system made livestock farming difficult.
考题
Which of the following statements is NOT true?（）A、The open field system provided a good opportunity to experiment.B、The open field system wasted land.C、The open field system was wasteful of labor and time.D、The open field system made livestock farming difficult.
考题
单选题According to the passage, the Earth’s magnetic field has _____.A
begun to change in the opposite directionB
been weakening in strength for a long timeC
caused the changes on the polaritiesD
misguided many a man and animal
考题
单选题Which of the following statements is NOT true?（）A
The open field system provided a good opportunity to experiment.B
The open field system wasted land.C
The open field system was wasteful of labor and time.D
The open field system made livestock farming difficult.
考题
单选题If a magnetic compass is not affected by any magnetic field other than the Earth’s，which statement is TRUE? （）A
Compass error and variation are equalB
Compass north will be true northC
Variation will equal deviationD
There will be no compass error
考题
单选题The coil of wire rotating in the magnetic field produces the（）.A
voltageB
currentC
powerD
frequency
考题
单选题（） is arranged for cleaning the lubricating oil in the system and clean oil can be provided from a storage tank.A
A filterB
A centrifugeC
A distillerD
A generator
考题
单选题To increase the frequency of an operating AC generator, you should （）A
increase the field excitationB
decrease the field excitationC
increase the number of magnetic polesD
increase the speed of the prime mover
考题
单选题Geological evidence suggests that the earth’s magnetic polarity has switched back and forth many times over the millennia; such ______in the magnetic field may affect the ability of our planet to ward off cosmic radiation.A
intensificationsB
justificationsC
recordsD
correlationsE
fluctuations
考题
单选题During the transition of the Earth’s magnetic field _____.A
the compass will become uselessB
man and animals will be confused as to directionsC
the magnetic strength of the Earth will disappearD
the magnetic strength of the Earth will be stronger
考题
单选题When placed in a magnetic field, which of the materials listed will maintain the highest permeability?（）A
GlassB
BakeliteC
Soft ironD
Aluminum
考题
单选题According to the passage, _____.A
we should not worry about the transition of the Earth’s magnetic fieldB
the Earth’s magnetic field will not change for at least 2000 yearsC
the Earth’s magnetic field has decreased its strength rapidlyD
the transition of the Earth’s magnetic field can be controlled by modern science
考题
单选题The energy consumed by an AC motor, as strictly reactive power, is （）A
used to do mechanical workB
used to establish the magnetic field of the motorC
lost as heat generated by the windingsD
lost in doing work to turn the motor itself
考题
单选题Permanent magnetism is caused by（）.A
operation of electrical equipment and generators on board shipB
the earth's magnetic field affecting the ship's hard iron during constructionC
the horizontal component of the earth's magnetic field acting on the horizontal soft ironD
the vertical component of the earth's magnetic field acting on the vertical soft iron
考题
单选题A ship under construction or major repair will acquire permanent magnetism due to（）while sitting stationary in the earth’s magnetic field.A
hammering and jarringB
vibration and poundingC
varying magnetic fieldsD
stable or permanent magnetism of the ship
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