【单选题】【消耗次数:1】
一台三相四极异步电动机,额定转差率是 0.04,若电源频率是50Hz,则电动机的转速为( )。
1440r/min
1450r/min
1000r/min
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相关题目
【单选题】 一台三相异步电动机的磁极对数p=2,电源频率为50Hz,电动机转速n=1440r/min,其转差率s为( )。
①  1%
②  2%
③  3%
④  4%
【简答题】 两台三相异步电动机的电源频率为50Hz,额定转速分别为1440r/min和2910r/min,则它们的磁极数分别是多少?额定转差率分别是多少?
【单选题】 三相异步电动机的额定转速为 nN = 970r/min, 则其额定转差率为( )。
①  0.04
②  0.03
③  0.02
【判断题】 一台6极三相异步电动机接于50Hz的电源上,转速为960r/min。此时电 动机的转子电流频率为2Hz。
①  正确
②  错误
【单选题】 一台三相异步电动机的转速为720 r/min,应选择电动机的磁极数为
①  八极
②  六极
③  四极
【单选题】 三相异电动机的转速为n=970r/min,则其额定转差率sN=
①  0.04
②  0.03
③  0.02
【单选题】 已知一台异步电动机转子的额定转速为1430r/min,那么这台电机的极对数为( )
①  2
②  4
③  6
④  1
【单选题】 已知某电动机的同步转速为1500r/min,其转子转速有可能是( )r/min。
①  1200B
②  1450C
③  1650
④  2900
【判断题】 一台6极船用柴油发电机,额定频率为50Hz,其额定转速为960r/min。
①  正确
②  错误
【单选题】 一台三相异步电动机,定子旋转磁场磁极对数为2,若定子电流频率为100Hz,其同步转速为( )。
①  1200r/min
②  1500r/min
③  2000r/min
④  3000r/min
随机题目
【单选题】 We must____________ the truth of the matter.
①  call out
②  pick out
③  go out
④  find out
【单选题】 My father bought me a bicycle____________ I could get to school quickly.
①  so as to
②  so on
③  so that
④  so much
【单选题】 For many people today, reading is no longer relaxation. To keep up their work they must read letters, reports, trade publications, interoffice communications, not to mention newspapers and magazines: a never-ending flood of words. In getting a job or advancing in one, the ability to read and comprehend quickly can mean the difference between success and failure. Yet the unfortunate fact is that most of us are poor readers. Most of us develop poor reading habits at an early age, and never get over them. The main problem lies in language itself—words. Single words have little meaning until they are combined into phrases, sentences and paragraphs. Unfortunately, however, the untrained reader does not read groups of words. He reads one word at a time, often regressing to reread words or passages. Regression, or looking back over what you have just read, is a common bad habit in reading. Another habit which slows down the speed of reading is vocalization—sounding each word either orally or mentally as one reads. To overcome these bad habits, some reading clinics use a device called accelerator (加速器), which moves a bar down the page at a predetermined speed. The bar is set at a slightly faster rate than the reader finds comfortable, in order to “stretch” him. The accelerator forces the reader to read fast, making word-by-word reading, regression and vocalization virtually impossible. At first, comprehension is sacrificed for speed. But when you learn to read ideas, you will not only read faster, but your comprehension will improve. Many people have found their reading skills improved a lot after some training.What does “At first, comprehension is sacrificed for speed” (Para. 2) mean?
①  The reader reads fast, but he understands everything he reads.
②  The reader reads slowly and he understands everything he reads.
③  The reader reads fast without understanding everything he reads.
④  The reader reads slowly, but he doesnt understand everything he reads.
【单选题】 For many people today, reading is no longer relaxation. To keep up their work they must read letters, reports, trade publications, interoffice communications, not to mention newspapers and magazines: a never-ending flood of words. In getting a job or advancing in one, the ability to read and comprehend quickly can mean the difference between success and failure. Yet the unfortunate fact is that most of us are poor readers. Most of us develop poor reading habits at an early age, and never get over them. The main problem lies in language itself—words. Single words have little meaning until they are combined into phrases, sentences and paragraphs. Unfortunately, however, the untrained reader does not read groups of words. He reads one word at a time, often regressing to reread words or passages. Regression, or looking back over what you have just read, is a common bad habit in reading. Another habit which slows down the speed of reading is vocalization—sounding each word either orally or mentally as one reads. To overcome these bad habits, some reading clinics use a device called accelerator (加速器), which moves a bar down the page at a predetermined speed. The bar is set at a slightly faster rate than the reader finds comfortable, in order to “stretch” him. The accelerator forces the reader to read fast, making word-by-word reading, regression and vocalization virtually impossible. At first, comprehension is sacrificed for speed. But when you learn to read ideas, you will not only read faster, but your comprehension will improve. Many people have found their reading skills improved a lot after some training. Most people cant read and comprehend quickly mainly because __________.
①  they dont read groups of words
②  they dont realize they have poor reading habits
③  they dont like to be trained in reading skills
④  they dont understand words when put together
【单选题】 Look!____________
①  Here your sister comes.
②  Here comes your sister.
③  Comes here your sister.
④  Your sister come here.
【单选题】 Goats are being hired to do the work of people near San Diego. The fires that occurred in Hillborbough four years ago destroyed thirty homes, most of which have been rebuilt. While people were rebuilding the homes, the grasses and bushes were growing back. The area is now so overgrown in bushes that there is again a major danger of fire.The city government put up bids to remove the bushes. The lowest bid they received was $50,000—and that was if the city provided breakfast and lunch for the workers for the six weeks it would take to clear the overgrown area. The city only wanted to give unlimited coffee and a piece of bread a day for each person. When that offer was rejected, the city asked for help on its website.A sheepherder in Montanta and a goat-keeper in San Bernardino read about the city’s plight(困境)while surfing the Web. They both offered to do the job for $25,000. The city government chose the goat-keeper because he lived closer. When he was told that the city dump(垃圾场)was overflowing , the goat-keeper said, “No problem. My goats will eat everything in your dump, except the car engines, of course.” So, for another $5,000, the city killed two birds with one stone. If all goes well, they will invite the goat-keeper and his “family” back every three years. The goat-keeper said that he would probably visit San Diego while his goats were in the dump.According to the passage, __________.
①  the sheepherder offered to do the job for $50,000
②  the lowest bid to remove the bushes was $50,000
③  the sheepherder and the goat-keeper were both addicted to surfing the Internet
④  hiring goats to do the job saved the city government lots of money
【单选题】 He____________ working as if nothing had happened.
①  continue
②  continues
③  continuing
④  continued
【单选题】 The twentieth century is the age of _____________.
①  technic
②  technician
③  technology
④  technological
【单选题】 Some scientists____________ that flowers open at particular times because their internal clocks tell them to do so.
①  receive
②  make
③  believe
④  talk
【单选题】 Client: Hello! May I speak to Mr. Turner?Secretary: ___________
①  I’m sorry. He’s at a meeting now..
②  I am. Speak, please.
③  Hello! Who’re you, please?
④  Hello! Thank you for calling.