【单选题】
单相桥式整流电路的直流输出电压是输入电压的___。
A. 45％；
B. 1．4l倍；
C. 90％；
D. 1．2倍；
查看试卷，进入试卷练习
微信扫一扫，开始刷题
相关试题
【单选题】
三相桥式整流电路的直流输出电压是输入电压的___。
A. 90％；
B. 1．4l倍；
C. 45％；
D. 2．34倍；
【单选题】
全波整流电路中每个二极管承受的最大反向电压为半波整流电路中的___。
A. 2倍；
B. 1．41倍；
C. 45％；
D. 2．82倍；
【单选题】
晶闸管是一种工作在开关状态下的___半导体器件。
A. 小功率；
B. 低频；
C. 高频；
D. 大功率；
【单选题】
晶闸管的导通条件是阳极一阴极加___电压且( )死区电压，控制极一阴极加正向触发电压。
A. 正向；小于；
B. 正向；大于；
C. 反向；小于；
D. 反向；大于；
【单选题】
晶闸管有阳极.阴极和控制极，其内有___PN结。
A. 2个；
B. 3个；
C. 4个；
D. 5个；
【单选题】
在晶闸管整流电路中，输出电压随晶闸管控制角的增加而___。
A. 不变；
B. 无关；
C. 增加；
D. 减小；
【单选题】
晶闸管单相整流电路电阻负载的最大移相范围是___。
A. 360’；
B. 180’；
C. 210’；
D. 120’；
【单选题】
可控整流即把交流电变换成大小可调的直流电，它是___技术的基础。
A. 变频；
B. 变压；
C. 变流；
D. 变换功率；
【单选题】
对于负载较小.电压波动要求不十分严格的电路，可采用并联___的稳压电路。
A. 电阻；
B. 电容；
C. 稳压管；
D. 电感；
【单选题】
对稳压精度要求高时，应采用___稳压电路。
A. 并联；
B. 串联；
C. 并串联；
D. 串并联；
【单选题】
稳压管内阻___，稳压性能越好。
A. 为0；
B. 趋于；
C. 越大；
D. 越小；
【单选题】
逆变整流电路是先把直流逆变成交流，然后再把交流又整流成___的过程。
A. 交流；
B. 直流；
C. 交直流；
D. 脉动直流；
【单选题】
逆变电路的作用是将直流电变成频率可变的或某一固定频率的___。
A. 直流电；
B. 交流电；
C. 高频电源；
D. 低频电源；
【单选题】
逆变电路UPS电源不宜带___负载。
A. 电阻性；
B. 电容性；
C. 电感性；
D. 混合型；
【单选题】
凝汽式发电厂的特点是___。
A. 建设周期短，基建投资较小；
B. 燃料利用总效率较高；
C. 利用电能产生热能向用户供给；
D. 建设在用户附近；
【单选题】
供热式发电厂的特点是___。
A. 建设周期短，基建投资较小；
B. 燃料利用总效率较高；
C. 利用电能产生热能向用户供给；
D. 建设在靠近燃料的产地；
【单选题】
提高输电电压，可以提高___。
A. 电能质量；
B. 输电电流；
C. 功率损耗；
D. 电能损耗；
【单选题】
电力系统是由发电机.___和用电设备组成。
A. 输电线路；
B. 配电线路；
C. 电力变压器；
D. 电力网；
【单选题】
担负着输送电能和分配电能任务的是___。
A. 电力系统；
B. 电力线路；
C. 电力网；
D. 配电网；
【单选题】
电力网是指由___组成的网络。
A. 各电压等级的电力线路；
B. 各电压等级的电力线路和各类变电所；
C. 发电机变压器.输电线路；
D. 一个电压等级的配电线路；
【单选题】
输电网是由___的输电线路和与其相连的变电所组成。
A. 35KV及以下；
B. 35KV及以上；
C. 110KV及以下；
D. 110KV及以上；
【单选题】
1000KV及以上的电力网称为___电力网。
A. 超高压；
B. 特高压；
C. 高压；
D. 中压；
【单选题】
我国电力系统额定频率为 50 Hz,3×10 kW 及以上系统允许频率偏差不超过___。
A. ±5%；
B. ±10%；
C. ±0.2 Hz；
D. ±0.5 Hz；
【单选题】
《全国供用电规则》规定，35 k V 及以上供电系统，电压变换幅度不超过___。
A. ±5%；
B. ±7%；
C. ±0.2 % ；
D. ±10 %；
【单选题】
频率是供电质量标准之一，我国电力系统的额定频率为___。
A. 0.02 s ；
B. 0.2 s；
C. 50 Hz；
D. 60 Hz；
【单选题】
由发电厂.输配电网络及各类电力用户组成的整体称为___。
A. 电力系统；
B. 电力网；
C. 输电线路；
D. 配电网；
【单选题】
发电厂在任何时刻发出的功率必须等于该时刻用电设备所需的功率与输送和分配环节中的___之和。
A. 无功功率；
B. 损失功率；
C. 机械功率；
D. 视在功率；
【单选题】
由输电线路和相连的变电所组成的部分称为___。
A. 电力系统；
B. 电力网；
C. 输电线路；
D. 配电网；
【单选题】
一切不正常的相与相之间或相与地之间的连通统称为___。
A. 短路；
B. 通路；
C. 回路；
D. 断路；
【单选题】
短路电流比正常电流大许多倍，而且会产生___效应，使导体之间产生很大的机械应力。
A. 作用力；
B. 反作用力；
C. 电动力；
D. 扭力；
【单选题】
一相对地之间的短路与电力系统中性点的接地方式___。
A. 有关；
B. 无关；
C. 关系不确定；
D. 关系不大；
【单选题】
电气设备在短路电流电动力的作用下，可发生___变形.瓷件拉坏等破坏作用，使事故进一步扩大。
A. 硬母线；
B. 电气设备；
C. 基础；
D. 构架；
【单选题】
短路持续时间长，可造成并列运行的发电机失去___。
A. 电压；
B. 控制；
C. 同步；
D. 励磁；
【单选题】
三相系统中中间相在三相短路时所受的电动力___。
A. 比两相短路时所受的电动力大；
B. 比两相短路时所受的电动力小；
C. 与两相短路时所受的电动力相同；
D. 无法确定；
【单选题】
短路电流通过电气设备，使设备发热___，持续时间长可使设备过热损坏。
A. 严重；
B. 增加；
C. 减少；
D. 不变；
【单选题】
发生三相金属性短路时，在短路点将产生___，使设备严重损坏。
A. 故障；
B. 电弧；
C. 破坏；
D. 大电流；
【单选题】
下列关于短路电流的发热，___是正确的。
A. 单相接地时发热大；
B. 两相短路时发热大；
C. 三相短路时发热大；
D. 所有短路发热一样大；
【单选题】
系统在最大运行方式下运行时，具有___短路阻抗值。
A. 最小；
B. 最大；
C. 平均；
D. 较大；
【单选题】
系统发生短路后产生的短路电流最大的一种运行方式，称为___运行方式。
A. 最小；
B. 最大；
C. 事故；
D. 正常；
【单选题】
因运行方式改变使阻抗变小，那么短路电流将___
A. 增大；
B. 减小；
C. 不变；
D. 异常；
推荐试题
【单选题】
What does integrity mean? ___
A. You do what you do because it's fashionable.
B. You do what you do because it's politically correct.
C. You do what you do because it's right.
D. You do what you do because somebody asked you to.
【单选题】
Is there cheating in World Cup? ___
A. It's none.
B. It's rare.
C. It's some.
D. It's popular.
【单选题】
Which one of the following situations is NOT mentioned for making us upset? ___
A. Some reward we thought we deserved has been denied us.
B. Some man we helped has proved ungrateful.
C. Some man we believed to be a friend has betrayed us.
D. Some woman we believed to be a friend has spoken ill of us.
【单选题】
In which year the Tour of France was hit by a drug-taking scandal? ___
A. In 1996.
B. In 1997.
C. In 1998.
D. In 1999.
【单选题】
Cheap fake products are everywhere except ___
A. clothes.
B. cut-price DVDs.
C. cut-price CDs.
D. cosmetics.
【单选题】
What should we do after exercise? ___
A. Stretch the muscles.
B. Have a sleep.
C. Maintain high body temperature.
D. Take a shower.
【单选题】
What shouldn’t we wear when we exercise? ___
A. Properly fitted sportswear.
B. Well-fitted sneakers.
C. Tight pants.
D. Sports bra for women.
【单选题】
Which of the following is NOT good for health? ___
A. Training with a friend.
B. Slack off a fitness regimen.
C. Keep our body hydrated.
D. Take small sips every few minutes.
【单选题】
What does the speaker do? ___
A. Public relations consultant.
B. Home cook.
C. Website administrator.
D. Writer.
【单选题】
Which is NOT included in the speaker’s favorite breakfasts? ___
A. Egg.
B. Prosciutto.
C. Papaya.
D. Cabbage.
【单选题】
When do the students start learning Chinese? ___
A. Since kindergarten
B. Since elementary school
C. Since middle school
D. Since high school
【单选题】
When can the students continue studying Chinese? ___
A. In elementary school and middle school.
B. In middle school and high school.
C. In high school and university
D. After the university.
【单选题】
How many American students are currently learning Chinese? ___
A. About 22,000
B. About 24,000
C. About 44,000
D. About 2,400
【单选题】
How much did the Defense Department give Oregon schools? ___
A. $70,000
B. $1.3 million
C. $700,000
D. $1.3 billion
【单选题】
What’s Isabel Weiss’s purpose of learning Chinese? ___
A. For fun
B. For more opportunities for jobs
C. For more opportunities of making money
D. For more opportunities for promotions
【单选题】
What ability do the standardized tests reward to? ___
A. Think.
B. Create.
C. Quickly answer superficial questions.
D. Above all.
【单选题】
In what ways the IQ scores can be changed? ___
A. Training.
B. Nutrition.
C. More friendly people administered the test.
D. Above all
【单选题】
What do schools focus on? ___
A. Concepts.
B. Science.
C. Social Studies.
D. Foreign languages.
【单选题】
Why tests and standards are a necessary fact of life? ___
A. They protect us from hazardous products.
B. They protect us from inept drivers.
C. They protect us from shoddy professionals.
D. Above all.
【单选题】
How many percent did the scores on statewide tests rise? ___
A. 4%.
B. 14%.
C. 40%.
D. None.
【单选题】
What was the woman’s reaction when she was nominated? ___
A. She was surprised at the nomination.
B. She was calm at the nomination.
C. She was indifferent to the nomination.
D. She was scared of the nomination.
【单选题】
According to the woman, who paid for her trip to San Francisco? ___
A. Her trip to San Francisco was sponsored by the Academy.
B. Her trip to San Francisco was paid for by her company.
C. Her trip to San Francisco was paid for by her family.
D. Her trip to San Francisco was paid for by herself.
【单选题】
What is the name of George Miller’s new movie? ___
A. Happy Feeling.
B. Happy Dancing.
C. Happy Foot.
D. Happy Feet.
【单选题】
Which name is not mentioned in the film? ___
A. Nicole Kidman.
B. Hugh Jackman.
C. George Clooney.
D. Robin Williams.
【单选题】
Which of the following statement is not true about “Life in the Freezer”? ___
A. It was a documentary film.
B. It was made by National Geographic and the BBC.
C. It was a story of the amazing life of Emperor penguins.
D. The
E. mperor penguin sang to each other to find a mate and made friends.
【单选题】
What should you do during a high-pressure periods? ___
A. Lock yourself in a room with your work.
B. Leave your work and go on a vocation.
C. Tell your boss you can’t finish your work.
D. Get together with people who will revitalize and inspire you.
【单选题】
Which of the following is the correct description of TempWorld? ___
A. The era of guaranteed jobs is history.
B. We are all temporary workers.
C. You have to equip yourself with the skills.
D. All of the above.
【单选题】
What should a career activist do? ___
A. Being a career activist means concentrating on daily business.
B. Being a career activist means you can do a business as long as it meets your short-term needs.
C. A career activist should take the long view of his career.
D. A career activist should plan everything in advance.
【单选题】
What should you do in the TempWorld? ___
A. In TempWorld you must withstand disappointment, juggle stressful situations, and handle pressure.
B. You must learn from your setbacks and use them to your advantage in the future.
C. Things always go well for successful people because they are honest.
D. Both A and B.
【单选题】
Which of the following statements is Not True? ___
A. Your boss may be willing to change his behavior than your think.
B. Some managers don’t care how much their words or actions upset staffers.
C. You should tell your managers how their outbursts make you feel.
D. If the boss values your work, he may stop his abusiveness.
【单选题】
Which of the following public places is NOT mentioned that have banned mobiles? ___
A. restaurants
B. gas stations
C. theatres
D. museums
【单选题】
What happened when the cellphone of the speaker’s friend rang? ___
A. His friend answered the phone and the speaker became invisible to his friend.
B. They answered the phone together.
C. The speaker threw away his friend’s cellphone.
D. His friend hung up the phone and kept talking to the speaker. (C)
【单选题】
What happened to the man? ___
A. He had a car accident.
B. He had his arms broken.
C. He lost his mobile phone.
D. He was not able to use his mobile because he was in a remote area.
【单选题】
Which of the following is NOT true? ___
A. Today there are about 400 million cellphone owners.
B. Today there are about 300 million Personal Computer subscribers.
C. Cellphones will be more often used.
D. Cellphones will completely replace Personal Computers.
【单选题】
Which of the following is true? ___
A. Ellen Johnson-Sirleaf stayed in her country during the nation’s civil war.
B. She is still working for the United Nations.
C. She is the first woman ever elected president of an Asian country.
D. She is a Liberia.
【单选题】
What do you know about the solar eclipse? ___
A. Only hundreds of people gazed at it.
B. It was caused by the earth passing in front of the moon.
C. It was not often seen.
D. It started in Mongolia and ended in Brazil.
【单选题】
What is true about this meeting between the USA and China? ___
A. It was a meeting between Xi Jinping and Donald Trump.
B. It was the first time that the Chinese president had visited the United States.
C. The issue of the Olympics was discussed.
D. South Korea’s nuclear weapons program was discussed.
【单选题】
In which year did the station’s first permanent crew arrived? ___
A. 1998
B. 2000
C. 2002
D. 2003
【单选题】
If elected, ________________. ___
A. Richardson would be the first Hispanic President.
B. Clinton would be the first African-American President.
C. Romney world be the first Hispanic President.
D. Clinton would be the first Mormon President.
【单选题】
What are the things that the speaker’s inner and outer life based on? ___
A. Money
B. Health
C.
D. elicious food
