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1、电大电工电子技术试题（三）期末复习考试资料 电大电工电子技术试题（三）期末复习考试资料 （三） 一、 填空题(每空 2 分，共 20 分) 1.稳压二极管有一个相对普通二极管较低的(反向击穿)电压。在特性曲线上，其反向击穿特性曲线很陡，击穿后在安全的工作电流范围内，能够保证电压变化(很小)。 2. 运放电路时常用到的三项理想化指标是开环差模电压放大倍数 Aod 为（无穷大）；差模输入电阻 Rid（无穷大）；差模输出电阻 Rod 为（零）。 3. 组合逻辑电路的特点是：从逻辑功能上看：（输出）只与（当时）输入的逻辑值有关，而与该时刻之前的输入及电路状态均（无关）。 4 D 触发器 1. 具有（置
2、位）、（复位）两种功能 二、 单项选择题（每题 4分，共 20 分） 1、图 1 所示电路中，电流表正负接线端用+、-号标出。今电流表指 针正向偏转，示数 10A，有关电流、电压方向也表示在图中，则（ C ）正确。 A. I1=10A，U=-6V B. I1=-10A，U=6V C. I1=10A，U=12V A 3 U I1 +- 20V3 24V3 6 10 图 1 2 2、图 2 所示电路中，判断电阻 R 中流通的电流及消耗的功率为（ B ）。 R + 2V - A. 0A，2W 1A B. 1A，2W 图 2 C. 1A，4W 3、在正弦交流纯电容电路中，电压与电流的关系是（ C ）。
3、 A. i= B. I= C. I=UC 4、已知电路某元件的电压 u 和电流 i 分别为 u=141cos（314t+600）V， i=7sin（314t-1200）A，则该元件的性质是（ A ）。 A. 电容 B. 电感 C. 电阻 5、在三相电路中，三相对称负载为星形连接，三个线电流均为 4A，则中线电流为（ C ）。 A.4A B.12A C. 0A 三、 计算题（每题 15 分，共 30 分） 1、用戴维南定理求图 3-1 电路中 R5 所在支路的电流。已知 R1=R2=R4=R5=5， B R3=10，U=6.5V。 R3 R1 D A R5 R4 R2 C + - U 图 3-1
4、 解：断开 R5，求开路电压 UO 和入端电阻R0 UBD= U4.33V UCD= U=3.25V UBC= UBD+UDC=UBD-UCD=1.08V 将 U 短路 R0= （R1/R3）+（R2/R4）5.83 求出电流 I5 为 I5=0.1A 2、一台三相异步电动机，磁极对数 p=2，工作额定电压为 380V，额定频率为 50Hz，已知额定转速为1450r/min，求其同步转速和额定转差率？ 解：1）同步转速 n1=1500r/min 2）额定转差率 sN=0.033 四、 简答题（每题 5 分，共 30 分） 1、负载增加的涵义是什么？在近似恒压源供电或近似恒流源供电系统中，负载增
5、加相当于负载电阻增大还是减小？ 负载增加意指电路的输出功率增加。在近似恒压源供电系统中，负载获得的功率 P=UI=，负载增加既是负载电流增大，相当于负载电阻减小。 在近似恒流源供电的系统中，负载获得的功率 P=UI=I2R，负载增加既是负载电压增大，相当于负载电阻加大。 2、在电路分析与计算中，戴维南定理最适宜应用于哪种情况？ 如果只需计算电路中某一支路的电流，此时最适宜采用戴维南定理。 3、三相交流电路中，负载星形连接时，相电流与线电流，相电压与线电压有何关系？ 相电流与线电流的关系为 IP=IL 相电压与线电压的关系为 UL=UP 4、三相异步电动机的调速方式主要有哪几种？ 有三种：（1）
6、改变电源频率调速；（2）改变转差率的调速；（3）异步电动机变极调速。 5、接触器分为哪两类？接触器的功能是什么？主要用于哪些地方？ 接触器是一种自动电器，有直流接触器和交流接触器之分，其功能是可以频繁的接通或断开交、直流电路及大容量控制电路。主要用于控制电动机、电热设备、电焊机等，尤其在电力拖动系统中应用广泛。 6. 边沿型 JK 触发器，在 CP 脉冲信号的作用下，其动作有何特点？（分为负边沿、正边沿两种情形） 答：负边沿型（下降沿触发型）：CP 下降沿到来的前一刻瞬间，J、K 接收输入；CP 下降沿到来后产生输出。正边沿型（上升沿触发型）：CP 上升沿到来前一刻瞬间，J、K 接收输入；CP
7、 上升沿到来后产生输出。 请您删除一下内容，O(_)O 谢谢！2021 年.电大期末复习考试小抄大全，电大期末考试必备小抄，电大考试必过小抄 After earning his spurs in the kitchens of The Westin, The Sheraton, Sens on the Bund, and a sprinkling of other top-notch venues, Simpson Lu fi nally got the chance to become his own boss in November 2021. Sort of. The Shanghai-
8、born chef might not actually own California Pizza Kitchen (CPK) but he is in sole charge of both kitchen and frontof- house at this Sinan Mansionsstalwart. Its certainly a responsibility to be the head chef, and then to have to manage the rest of the restaurant as well, the 31-year-old tells Enjoy S
9、hanghai. In hotels, for example, these jobs are strictly demarcated, so its a great opportunity to learn how a business operates across the board. It was a task that management back in sunny California evidently felt he was ready for, and a vote of confi dence from a company that, to date, has opene
10、d 250 outlets in 11 countries. And for added pressure, the Shanghai branch was also CPKs China debut. For sure it was a big step, and unlike all their other Asia operations that are franchises, they decided to manage it directly to begin with, says Simpson. Two years ago a private franchisee took ov
11、er the lease, but the links to CPK headquarters are still strong, with a mainland-based brand ambassador on hand to ensure the business adheres to its ethos of creating innovative, hearth-baked pizzas, a slice of PR blurb that Simpson insists lives up to the hype. They are very innovative, he says.
12、The problem with most fast food places is that they use the same sauce on every pizza and just change the toppings. Every one of our 16 pizza sauces is a unique recipe that has been formulated to complement the toppings perfectly. The largely local customer base evidently agrees and on Saturday and
13、Sunday, at least, the place is teeming. The kids-eat-for-free policy at weekends is undoubtedly a big draw, as well as is the spacious second-fl oor layout overlooked by a canopy of green from Fuxing Park over the road. The company is also focusing on increasing brand recognition and in recent years
14、 has taken part in outside events such as the regular California Week. Still, the sta are honest enough to admit that business could be better; as good, in fact, as in CPKs second outlet in the popular Kerry Parkside shopping mall in Pudong. Sinan Mansions has really struggled to get the number of v
15、isitors that were envisaged when it first opened, and it hasnt been easy for any of the tenants here, adds Simpson. Were planning a third outlet in the city in 2021, and we will probably choose a shopping mall again because of the better foot traffic. The tearooms once frequented by Coco Chanel and
16、Marcel Proust are upping sticks and coming to Shanghai, Xu Junqian visits the Parisian outpost with sweet treats. One thing the century-old Parisian tearoom Angelina has shown is that legendary fashion designer Coco Chanel not only had style and glamor but also boasted great taste in food, pastries
