题干

家用微波炉是一种利用微波的电磁能加热食物的新型灶具,它主要由磁控管、波导管、微波加热器、炉门、变压器、镇流系统、冷却系统、控制系统、外壳等组成.接通电路后,220 V交流电经变压器变压,在次级产生3.4 V低压交流电对磁控管加热,同时在另一次级产生2000 V高压电,经镇流系统加到磁控管的阴、阳两极之间,使磁控管产生微波.微波输送至金属制成的加热器(炉腔),被来回后射,微波的电磁作用使食物内的分子高频运动,从而使食物受热,并能最大限度地保存食物中的维生素.关于上述微波炉,下列说法正确的是(    )

A:微波是由于原子外层电子受激发而产生的

B:微波是由于原子内层电子受激发而产生的

C:微波炉变压器的低压变压比为1100:17

D:微波炉变压器的高压变压比为17:100000

上一题 下一题 0.0难度 选择题 更新时间:2019-12-02 11:09:23

答案(点此获取答案解析)

C

同类题1

任务型阅读

    Rather Public speaking and critical thinking

    What is critical thinking? To a certain degree, it's a matter of logic (逻辑) — of being able to spot weaknesses in other people's arguments and to avoid them in your own, it also includes related skills such as distinguishing fact from opinion and assessing the soundness of evidence .

    In the broad sense, critical thinking is focused, organized thinking – the ability to see clearly the relationships among ideas____The greatest thinkers, scientists, and inventors have often taken information that was really available and put it together differently to produce new ideas. That, too, is critical thinking.

    ____ As the class goes on, for example, you will probably spend a good deal of time organizing your speeches. While this may seem like a purely mechanical (机械的) exercise, it is closely connected with critical thinking. If the structure of your speech is loose and confused, chances are that your thinking is also disordered and confused. If, on the other hand, the structure is clear, there is a good chance your thinking is too. Organizing a speech is not a matter of arranging the ideas your already have____

    What is true of organization is true of many aspects of public speaking.____ As you work on expressing your ideas in clear accurate language, you will improve your ability to think clearly and accurately____ As you learn to listen critically to speeches in class, you will be better able to assess the ideas of speakers in a variety of situations.

    If you take full advantage of your speech class, you will be able to develop your skills as critical thinker in many circumstances. This is one reason public speaking has been regarded as a vital part of education since the days of ancient Greece.

A. Rather, it is an important part of shaping the ideas themselves.

B. This may seem like a lot of time, but the rewards are well worth it.

C. It may also help you to know that there is no such thing as a perfect speech.

D. As you study the role of evidence and reasoning in speechmaking, you will see how they can be used in other forms of communication as well.

E. The skills you learn in your speech class can help you become a more effective thinker in a number of ways.

F. If you are wondering what this has to do with your public speaking class, the answer is quite a lot.

G. It has often been said that there are few new ideas in the world, only reorganized ideas.