相关试题
【判断题】
直流电机电刷边缘大部分或全部有轻微的火花为2极火花。
【判断题】
直流电机换向过程也就是电枢绕组元件被电刷短路的过程。
【判断题】
直流电机产生火花的原因是由于电刷接触面电流密度太大所至。
【判断题】
直流电机换向极装在电机的几何中心线上。
【判断题】
直流电机减小电刷与换向片的接触电阻可以改善电机换向。
【判断题】
直流电机在正常使用过程中，温度升高会使电刷接触压降减小，可能引起换向不良。
【判断题】
在直流电动机中，电刷两端加的是直流电。’
【判断题】
在直流电动机中因电刷和换向器的作用，线圈内部为交流电。
【判断题】
直流电机电枢单波绕组的相邻绕组元件相隔约为三个极距。
【判断题】
电刷接触电阻的大小主要决定于电刷的材质和结构。
【判断题】
脉流牵引电动机通常采用固定分路电阻以降低主磁通的脉动程度。
【判断题】
直流牵引电机环火最根本的原因是换向器上电位特性过陡及片间电压过高。
【判断题】
直流电机定子的作用是产生磁场和作为电机的机械支撑。
【判断题】
直流电机的电枢在磁场中旋转时，电枢铁芯只产生涡流。
【判断题】
直流电动机的电磁转矩减小时，电动机转速将上升。
【判断题】
156·在交流电机的三相绕组中，通以三相相等电流，可以形成旋转磁场。
【判断题】
157·为了提高三相异步电动机的启动转矩，可使电源电压高于电机的额定电压，从而获得较好的启动性能。
【判断题】
158·电力机车上使用的牵引电动机有交流和直流之分，而这两种电动机的调速方法是基本相I司的。
【判断题】
159·对于正常运转需Y接法的笼型三相异步电动机，可采用Y／△降压启动方法启动。
【判断题】
三相异步电动机运行时，若转差率为零则电磁转矩也为零。
【判断题】
161·三相异步电动机的转子的转速越低，电机的转差率越大，转子电动势频率越高。
【判断题】
三相异步电动机的转速取决于电源频率和极对数，而与转差率无关。
【判断题】
三相异步电动机旋转磁场的旋转方向是由三相电流的相序决定的。
【判断题】
164·劈相机启动时应投入启动电阻后方能启动，当劈相机启动完成后必须切除启动电阻。
【判断题】
劈相机可实现单一三相供电系统的电压以及电流的对称供电特性。
【判断题】
166·旋转劈相机可自动启动而无需启动控制。
【判断题】
旋转劈相机是将单相交流电劈成三相交流电的装置。
【判断题】
168·电力机车运行方向的控制，采用改变牵引电动机电枢绕组的电流方向实现的。
【判断题】
电力机车运行中若要改变方向，必须在机车停车后才能转换。
【判断题】
170·电力机车上电器采用的冷却方式为风冷。
【判断题】
172-碱性蓄电池充电过程中，电解液密度升高。
【判断题】
175·当代铁路机车三大高科技技术：交直流传动技术、微机控制技术和径向可调节转向架技术(径向自导向轮对)。
推荐试题
【单选题】
Nancy is considered to be _________ the other students in her class.___
A. less intelligent
B. the most intelligent
C. intelligent as well
D. as intelligent as
【单选题】
She is not only my classmate __________ also my good friend.___
A. or
B. but
C. and
D. too
【单选题】
I would like to do the job ________ you don't force me to study.___
A. in case
B. although
C. though
D. as long as
【单选题】
__________ she survived the accident is miracle.___
A. What
B. That
C. As
D. Which
【单选题】
I often see _________ the road on his way home.___
A. he cross
B. him cross
C. him crossed
D. he crossing
【单选题】
The workers are busy __________ models for the exhibition.___
A. to make
B. with making
C. being making
D. making
【单选题】
The higher the temperature, __________ the liquid evaporates.___
A. the faster
B. the more fast
C. the slower
D. the more slower
【单选题】
Australia is one of the few countries ___________ people drive on the left of the road.___
A. which
B. that
C. where
D. on which
【单选题】
The grey building is the place where the workers live, and the white building is the place where the spare parts _________ .___
A. are producing
B. are produced
C. produced
D. being produced
【单选题】
Once environmental damage ___________, it takes many years for the system to recover.___
A. is to do
B. does
C. had done
D. is done
【单选题】
We worked hard and completed the task ________.___
A. in the time
B. on the time
C. ahead of time
D. before time
【单选题】
I didn't expect you to turn __________ at the meeting yesterday.___
A. up
B. to
C. out
D. over
【单选题】
Mike is better than Peter _________ swimming.___
【单选题】
Eggs, though rich in nourishments, have ___________ of fat.___
A. a large number
B. the large number
C. a large amount
D. the large amount
【单选题】
His salary as a driver is much higher than _____________.___
A. a porter
B. is a porter
C. as a porter
D. that of a porter
【单选题】
I have been looking forward to__________ from my parents.___
A. hear
B. being heard
C. be heard
D. hearing
【单选题】
The manager will not __________ us to use his car.___
A. have
B. let
C. agree
D. allow
【单选题】
__________ her and then try to copy what she does.___
A. Mind
B. See
C. Stare at
D. Watch
【单选题】
It's bad __________ for you to smoke in the public places where smoking is not allowed.___
A. behavior
B. action
C. manner
D. movement
【单选题】
— I think John and Peter will.___
A. carry out
B. get through
C. take in
D. set aside
【单选题】
If she wants to keep slim, she must make a ________ in her diet.___
A. change
B. turn
C. run
D. go
【单选题】
___________ the War of Independence, the United States was an English colony.___
A.
B. efore B. At
C. In
D. Between
【单选题】
A police officer claimed he had attempted to _________ paying his fare.___
A. avoid
B. reject
C. refuse
D. neglect
【单选题】
He is not seriously ill, but only a _________ headache.___
A. obvious
B. delicate
C. slight
D. temporary
【单选题】
On average, a successful lawyer has to talk to several _________ a day.___
A. customers
B. supporters
C. guests
D. clients
【单选题】
What is the train _________ to Birmingham?___
A. fee
B. tip
C. fare
D. cost
【单选题】
He put forward a theory, _______ of great importance to the progress of science of technology.___
A. I think which is
B. which I think is
C. which is I think
D. I think it is
【单选题】
If the doctor had been available, the child ____________.___
A. would not die
B. could not have died
C. might not die
D. should not have died
【单选题】
The music sounded _______. I enjoyed every minute of it.___
A. well
B. boring
C. wonderfully
D. beautiful
【单选题】
Put it down, Richard. You mustn't read ______letter. ___
A. anyone's else's
B. anyone's else
C. anyone else's
D. anyone else
【单选题】
I saw that she was in difficulty with all those parcels, so I offered my_____.___
A. service
B. money
C. use
D. chance
【单选题】
We were all surprised when he made it clear that he _____________office soon.___
A. leaves
B. would leave
C. left
D. had left
【单选题】
The electric fan has blown away the terrible smell in the hall, ______?___
A. can't it
B. isn't it
C. hasn't it
D. doesn't it
【填空题】
In every cultivated language there are two great classes of words which, taken together, comprise the whole vocabulary. First, there are those words ___ which we become acquainted in daily conversation,
【填空题】
which we ___,that is to say, from the members of our own family and from our familiar associates,
【填空题】
and which we should know and use ___ we could not read or write.
【填空题】
They ___the common things of life,
【填空题】
and are the stock in trade of all who___the language. Such words may be called “popular”,
【填空题】
since they belong to the people___and are not the exclusive share of a limited class. On the other hand,
【填空题】
our language___a multitude of words which are comparatively seldom used in ordinary conversation. Their meanings are known to every educated person,
