電工電子技術(shù)模擬題（四）

1、電工電子技術(shù)模擬題（四） 電工電子技術(shù)模擬題（四） 一、 填空題(每空 2 分，共 20 分) 1、三相交流電路中，對稱負載三角形連接時，相電流與線電流的關(guān)系為(il=ip), 相電壓與線電壓的關(guān)系為(up=ul) 2、引入負反饋對放大電路能起到穩(wěn)定(靜態(tài))工作點，提高放大倍數(shù)的穩(wěn)定性，改變(輸入、輸出)電阻，減小(失真)，拓展通頻帶等。 3.所謂控制電器，是指在電路中起(通斷)、保護、(控制)、調(diào)節(jié)的電器件. 4. 主從型觸發(fā)器，其動作特點是：時鐘 cp(上升沿)到來前一刻瞬間，j、k(接收)輸入信號，并要求在 cp=1 期間，輸入狀態(tài)保持穩(wěn)定。時鐘下降沿到來后產(chǎn)生(輸出)。 二、 單項選擇

2、題（每題 4 分，共 20 分） i 1、圖 1 所示電路中，電流 i 為（ b ） 3a + 30v - a. -3v 6 b. 5a 圖 1 c. 2a 2、圖 2 所示電路中，電位器 rp1的滑動端向下移動及 rp2 的滑動端向右移 動 i2 時，電流 i1、i2 的變化趨勢是（ b ）。 rp2 rp1 i1 is a. i1 減小，i2 增大 圖 2 b. i1 增大，i2 減小 c. i1 不變，i2 減小 3、在正弦交流純電感電路中，電壓與電流的關(guān)系是（ c ）。 a. i= b. i= c. i= 4、已知電路某元件的電壓 u 和電流 i 分別為 u=10cos（t+200）v

3、， i=5sin（t+1100）a，則該元件的性質(zhì)是（ c ）。 a. 電容 b. 電感 c. 電阻 5、磁力線上任意一點的切線方向，就是該點的磁場方向，即小磁針在磁力作用下（ a ）極所指的方向。 a. n 極 b. s 極 c. n 極或 s 極 三、 計算題（每題 15 分，共 30 分） 1、已知某正弦電壓在 t=0 時，其值 u0=110v，初相為 600，求其有效值。 解：正弦電壓瞬時表達式為 u=umcos（t+600） 當 t=0 時， u0= umcos600 故有 um=220v u=220v 2、已知交流信號源的內(nèi)阻為 250 歐姆，通過一個變壓比可調(diào)的變壓器接 2.5

4、歐姆的負載 rl，當變壓器初級的等效電阻等于信號源內(nèi)阻時，信號源的輸出功率最大，要使負載獲得最大功率，問變壓器的變壓比應(yīng)該是多少？ 解：根據(jù)=k2，變壓器初級的等效電阻 rl= k2rl=2.5k2 當變壓器初級的等效電阻等于信號源內(nèi)阻時，信號源的輸出功率最大，所以： rl= k2rl=2.5k2=250 k2=100 所 以當變壓比 k=10 時，負載將獲得最大功率。 四、 簡答題（每題 5 分，共 30 分） 1、電壓源模型與電流源模型等效變換的條件是什么？ 如果電壓源模型的輸出電壓和輸出電流與電流源模型的輸出電壓和輸出電流對應(yīng)相等，既是說，對同一外部電路而言，二者的伏安特性相同，那么兩種

5、模型可以等效互換。 2、何為三要素？自行在正弦交流電量瞬時波形圖上標出 3 要素。 幅值、頻率、初相 3、異步電動機起動的要求是什么？說明原因。 （1）有足夠大的起動轉(zhuǎn)矩，使電動機能克服負載轉(zhuǎn)矩迅速旋轉(zhuǎn)起來。 （2）起動電流不要太大，否則會對供電電網(wǎng)產(chǎn)生比較大的電壓降，從而影響電網(wǎng)上其它電氣設(shè)備的正常工作。 4、什么是正向偏置和反向偏置？二極管在正向偏置和反向偏置時分別為什么狀態(tài)？ 答：當 pn 結(jié)的 p 區(qū)接電源正極，n 區(qū)接電源負極時，稱為外加正向電壓，也叫正向偏置。當 p 區(qū)接電源負極，n 區(qū)接電源正極時，稱為外加反向電壓，也叫反向偏置。 正向偏置時，二極管處于導(dǎo)通狀態(tài)；反向偏置時，二極

6、管處于截止狀態(tài) 5. 對組合邏輯電路的分析步驟是什么？ 答：在邏輯圖中，對每個門的輸出端加以標注；寫出每個門輸出的邏輯函數(shù)表達式；將每個門輸出的邏輯函數(shù)表達式進行迭代，并進行必要的化簡；最后寫出真值表，并說明該電路的用途。 請您刪除一下內(nèi)容，o(_)o 謝謝！2021 年.電大期末復(fù)習考試小抄大全，電大期末考試必備小抄，電大考試必過小抄 after earning his spurs in the kitchens of the westin, the sheraton, sens on the bund, and a sprinkling of other top-notch venues,

7、 simpson lu fi nally got the chance to become his own boss in november 2021. 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 mansionsstalwart. "its certainly a responsibility to be th

8、e 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 its a great opportunity to learn how a business operates across the board." it was a task that management

9、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 cpks china debut. "for sure it was a big step, and unlike all their other asia operation

10、s 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 creat

11、ing "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

12、 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 spa

13、cious 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 co

14、uld 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 visitors that were envisaged when it first opened, and it hasnt been easy for any of the tenants here," adds simpson. &

15、quot;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 marcel proust are upping sticks and coming to shanghai, xu junqian visits the parisian outpost with sweet

16、 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 frequen

17、ted 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 t

18、he 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

19、chanel once sat at every afternoon for hot chocolate. the famous hot chocolate, known as lafricain, is a luxurious mixture of four types of cocoa beans imported from africa, blended in paris and then shipped to shanghai. its sinfully sweet, rich and thick as if putting a bar of melting chocolate dir

20、ectly 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 b

21、ase. 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 worlds most competitive place for desserts. a much overlooked pairing, is the paris-n

22、ew 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

23、 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 sem

24、i-cooked foie gras terrine, is seductive and deceptive. its 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 dont actually need the toast for cr

25、unchiness. 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 fo

26、r 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-x