电工电子技术模拟题（四）

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　电工电子技术模拟题（四）

　 一、 填空题(每空 2 分，共 20 分) 1、三相交流电路中，对称负载三角形连接时，相电流与线电流的关系为(IL=IP), 相电压与线电压的关系为(UP=UL) 2、引入负反馈对放大电路能起到稳定(静态)工作点，提高放大倍数的稳定性，改变(输入、输出)电阻，减小(失真)，拓展通频带等。

　3.所谓控制电器，是指在电路中起(通断)、保护、(控制)、调节的电器件. 4. 主从型触发器，其动作特点是：时钟 CP(上升沿)到来前一刻瞬间，J、K(接收)输入信号，并要求在 CP=1 期间，输入状态保持稳定。时钟下降沿到来后产生(输出)。

　二、 单项选择题（每题 4 分，共 20 分）

　I 1、图 1 所示电路中，电流 I 为（ B ）

　• 3A + 30V - A. -3V 6Ω B. 5A 图 1 • C. 2A 2、图 2 所示电路中，电位器 RP1的滑动端向下移动及 RP2 的滑动端向右移 动 I2 时，电流 I1、I2 的变化趋势是（ B ）。

　RP2 RP1 I1 IS A. I1 减小，I2 增大 图 2 B. I1 增大，I2 减小 C. I1 不变，I2 减小 3、在正弦交流纯电感电路中，电压与电流的关系是（ C ）。

　A. i= B. I= C. I= 4、已知电路某元件的电压 u 和电流 i 分别为 u=10cos（ωt+200）V， i=5sin（ωt+1100）A，则该元件的性质是（ C ）。

　A. 电容 B. 电感 C. 电阻 5、磁力线上任意一点的切线方向，就是该点的磁场方向，即小磁针在磁力作用下（ A ）极所指的方向。

　A. N 极 B. S 极 C. N 极或 S 极 三、 计算题（每题 15 分，共 30 分）

　1、已知某正弦电压在 t=0 时，其值 u0=110V，初相为 600，求其有效值。

　解：正弦电压瞬时表达式为 u=Umcos（ωt+600）

　当 t=0 时， u0= Umcos600 故有 Um==220V U==220V 2、已知交流信号源的内阻为 250 欧姆，通过一个变压比可调的变压器接 2.5 欧姆的负载 RL，当变压器初级的等效电阻等于信号源内阻时，信号源的输出功率最大，要使负载获得最大功率，问变压器的变压比应该是多少？ 解：根据=K2，变压器初级的等效电阻 R＇L= K2RL=2.5K2 当变压器初级的等效电阻等于信号源内阻时，信号源的输出功率最大，所以：

　R＇L= K2RL=2.5K2=250 K2==100 所

　以当变压比 K=10 时，负载将获得最大功率。

　四、 简答题（每题 5 分，共 30 分）

　1、电压源模型与电流源模型等效变换的条件是什么？ 如果电压源模型的输出电压和输出电流与电流源模型的输出电压和输出电流对应相等，既是说，对同一外部电路而言，二者的伏安特性相同，那么两种模型可以等效互换。

　2、何为三要素？自行在正弦交流电量瞬时波形图上标出 3 要素。

　幅值、频率、初相 3、异步电动机起动的要求是什么？说明原因。

　（1）有足够大的起动转矩，使电动机能克服负载转矩迅速旋转起来。

　（2）起动电流不要太大，否则会对供电电网产生比较大的电压降，从而影响电网上其它电气设备的正常工作。

　4、什么是正向偏置和反向偏置？二极管在正向偏置和反向偏置时分别为什么状态？ 答：当 PN 结的 P 区接电源正极，N 区接电源负极时，称为外加正向电压，也叫正向偏置。当 P 区接电源负极，N 区接电源正极时，称为外加反向电压，也叫反向偏置。

　正向偏置时，二极管处于导通状态；反向偏置时，二极管处于截止状态 5. 对组合逻辑电路的分析步骤是什么？ 答：在逻辑图中，对每个门的输出端加以标注；写出每个门输出的逻辑函数表达式；将每个门输出的逻辑函数表达式进行迭代，并进行必要的化简；最后写出真值表，并说明该电路的用途。

　请您删除一下内容，O(∩_∩)O 谢谢！！！2015 年中央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 2010. Sort of. The Shanghai-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 Mansions＇stalwart.

　“It’s 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 Shanghai. “In hotels,

　for example, these jobs are strictly demarcated, so it’s 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 opened 250 outlets in 11 countries. And for added pressure, the Shanghai branch was also CPK’s 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 over 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. “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 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 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 CPK’s second outlet in the popular Kerry Parkside shopping mall in Pudong.

　“Sinan Mansions has really struggled to get the number of visitors that were envisaged when it first opened, and it hasn’t been easy for any of the tenants here,“ adds Simpson. “We’re planning a third outlet in the city in 2015, and we will probably choose a

　shopping mall again because of the better foot traffic.“ The tearooms once frequented by Coco Chanel and 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 in particular. One of the most popular tearooms in Paris, Angelina is famous for having once been frequented by celebrities such as Chanel and writer Marcel Proust. Now Angelina has packed up its French ambience, efficient service, and beautiful, comforting desserts and flown them to Shanghai. At the flagship dine-in and take-out space in Shanghai, everything mimics the original tearoom designed from the beginning of the 20th century, in Paris, the height of “Belle Epoque“. The paintings on the wall, for example, are exactly the same as the one that depicts the landscape of southern France, the hometown of the owner; and the small tables are intentional imitations of the ones that Coco Chanel once sat at every afternoon for hot chocolate. The famous hot chocolate, known as L’Africain, is a luxurious mixture of four types of cocoa beans imported from Africa, blended in Paris and then shipped to Shanghai. It’s sinfully sweet, rich and thick as if putting a bar of melting chocolate directly on the tongue and the fresh whipped cream on the side makes a light, but equally gratifying contrast. It is also sold in glass bottles as takeaway. The signature Mont-Blanc chestnut cake consists of three parts: the pureed chestnut on top, the vanilla cream like stuffing, and the meringue as base. Get all three layers in one scoop, not only for the different textures but also various flavors of sweetness. The dessert has maintained its popularity for a century, even in a country like France, perhaps the world’s most competitive place for desserts. A much overlooked pairing, is the Paris-New York choux pastry

　and N226 chocolate flavored tea. The choux pastry is a mouthful of airy pecan-flavored whipped cream, while the tea, a blend of black teas from China and Ceylon, cocoa and rose petals, offers a more subtle fragrance of flowers and chocolate. Ordering these two items, featuring a muted sweetness, makes it easier for you to fit into your little black dress. Breakfast, brunch, lunch and light supper are also served at the tearoom, “a hub of many cultures“ and takes in “a mix of different styles of French cuisines“, according to the management team. The semi-cooked foie gras terrine, is seductive and deceptive. It’s generously served at the size and shape of a toast, while the actual brioche toast is baked into a curved slice dipped with fig chutney. The flavor, however, is honest: strong, smooth and sublime. And you don’t actually need the toast for crunchiness. This is the season for high teas, with dainty cups of fine china and little pastries that appeal to both visual and physical appetites. But there is one high tea with a difference, and Pauline D. Loh finds out just exactly why it is special. Earl Grey tea and macarons are all very well for the crucial recuperative break in-between intensive bouts of holiday season shopping. And for those who prefer savory to sweet, there is still the selection of classic Chinese snacks called dim sum to satisfy and satiate. High tea is a meal to eat with eye and mouth, an in-between indulgence that should be light enough not to spoil dinner, but sufficiently robust to take the edge off the hunger that strikes hours after lunch. The afternoon tea special at Shang-Xi at the Four Seasons Hotel Pudong has just the right elements. It is a pampering meal, with touches of luxury that make the high tea session a treat in itself. Whole baby abalones are braised and then topped on a shortcrust pastry shell, a sort of Chinese version of the Western vol-au-vent, but classier. Even classier is the dim sum staple shrimp dumpling or hargow, upgraded with the addition of slivers

　of midnight dark truffles. This is a master touch, and chef Simon Choi, who presides unchallenged at Shang-Xi, has scored a winner again. Sweet prawns and aromatic truffles — what’s not to love? His masterful craftsmanship is exhibited in yet another pastry — a sweet pastry that is shaped to look like a walnut, but which you can put straight into the mouth. It crumbles immediately, and the slightly sweet, nutty morsel is so easy to eat you’ll probably reach straight for another.