五年级下英语期末模拟试卷全能练考牛津译林(一起)
牛津译林版五年级英语(下册)期末模拟题及答案

牛津译林版五年级英语(下册)期末模拟题及答案题序一二三四五六七八九十总分得分(满分:100分时间:60分钟)(听力部分40分)一、听录音,选出你所听到的单词,听两遍。
(10分)( ) 1. A.January B.June C.February( ) 2. A.December B.November C.September ( ) 3. A.English B.few C.year( ) 4. A.thanks B.trip C.game( ) 5. A.contest B.year C.riddle二、听录音,选择正确的图片,读两遍。
(10分)( ) 1. A. B.( ) 2. A. B.( ) 3. A. B.( ) 4. A. B.( ) 5. A. B.三、听录音,选择正确的答语,读两遍。
(10分)( ) 1. A.I’m from Bazhong. B.I live in Bazhong.( ) 2. A.They live in the rivers. B.They live in the desert.( ) 3. A.She’s going to play ping-pong. B.She’s playing ping-pong. ( ) 4. A.No, he doesn’t. B.He wears a T-shirt.( ) 5. A.Yes, I do. B.Because they have nice big tails. 四、听录音,根据所听内容补全短文,听两遍。
(10分)It's a sunny day. Some students are going on a trip. Look, Peter is ____________ a cake. Kate is doing the ____________ jump with Lisa. Amy and Sarah are telling ____________. Jack is reading a book. Mike is listening to music. John and Mr Black are ____________chess under the tree. Miss White is writing a report. They are____________ a good time today.(笔试部分60分)五、单项选择,将正确答案序号填在括号里。
牛津译林版五年级下册英语期末测试卷及答案

牛津译林版五年级下册英语期末测试卷及答案一、听力。
(每题1分,共15分)A.选出你所听到的图片。
A BC D E1. 2. 3. 4. 5.B.听句子选择相应的答语,每个句子读两遍。
( )6. A. It’s on Moon Street. B. I live in Park Town. C. You can take a bus. ( )7. A .It’s on the 18th of July. B. My birthday is in July.C. It’s in May or June.( )8. A. I like playing football. B. I’m watching TV. C. I should have a rest. ( )9. A. It’s two years olds. B. It’s ten yuan. C. It’s yummy. ( )10. A. I have a toothache. B. He feels cold.C. He usually does his homework.C.听下面五段对话,回答问题。
( )11. When is Yang Ling’s birthday?A. It’s on the eighth of June.B. It’s on the ninth of June.C. It’s on the tenth of June.( )12. What’ in the fridge?A. Some potatoes.B. Some potatoes and some meat.C. Some tomatoes ( )13. What does Nancy often do at weekends ?A. Goes to the cinema.B. Goes to the library.C. Goes to the park. ( )14. What is Mike doing?A. He’s drawing.B. He’s reading.C. He’s singing.( )15. How does David go to school?A. By bus.B. By taxi.C. By car.二、选择填空。
牛津译林版五年级英语(下册)期末考试卷及答案

牛津译林版五年级英语(下册)期末考试卷及答案题序一二三四五六七八九十总分得分(满分:100分时间:60分钟)(听力部分40分)一、听录音,选出你所听到的单词,听两遍。
(10分)( )1. A.lunch B.breakfast C.dinner( )2. A.quietly B.quick C.speak( )3. A.left B.right C.light( )4. A.song B.sing C.ring( )5. A.Canada B.Spanish C.Chinese二、听录音,选择正确的图片,读两遍。
(10分)( ) 1. A.B.C.( ) 2. A.B.C.( ) 3. A.B.C.( ) 4. A.B.C.( ) 5. A.B. C.三、听录音,选择正确的答语,读两遍。
(10分)( ) 1. A.Last Sunday.B.At school. C.It’s a dog.( ) 2. A.No, she doesn’t. B.No, he doesn’t. C.No, I don’t.( ) 3. A.I’m fine. B.I’m playing. C.Thank you.( ) 4. A.Yes, I did. B.Yes, I do. C.No, they don’t. ( ) 5. A.We went home. B.We went to the zoo. C.We went there by bus.四、听录音,根据所听内容补全短文,听两遍。
(10分)Hello, I'm John. I'm an English boy. My father is a _______ and my mother is a _______. My uncle and aunt are _______. They _______ in the countryside (乡下). I often _______ them. I see a lot of interesting animals _______. The _______ are my friends. They have fat bodies and short _______. They can _______. I like to feed (喂养) them. In _______, I like to pick _______. They're purple and sweet. I like the life on the _______.(笔试部分60分)五、单项选择,将正确答案序号填在括号里。
五年级下英语期末模拟试卷试卷5_牛津译林(一起)

五年级下英语期末模拟测试卷5带解析1.看图,写出相应的单词或词语。
〔5%〕2.Read and fill in blanks. (根据所给首字母,用单词的正确形式填空)〔5%〕〔1〕Zhang Peng is making a snowman.〔2〕I often play sports with my friends.〔3〕In spring, we can fly kites.〔4〕When's your birthday?〔5〕Which season do you like best?3.----What's your favourite season?----____________A. I like fall best.B. February is my favourite.C. I swim in summer.4.My parents usually get up ________ 6:40.on B. in C. at5.----What's the date today?----____________It's Tuesday. B. It's cool C. It's April 1st.6.----Is Amy answering the phone?----____________Yes, he does. B. No, she is writing a letter. C. No, he isn't. 7.August is the ________ month of the year.seven B. ninth C. Eighth8.---- What is Mike doing?---- He ____________running B. swims in the river C. is walking9. ----______ do you like summer?----______ I can swim in the river.Why, Because B. Why, And C. Which, Because10.将问题与答案连起来。
牛津译林版五年级英语(下册)期末检测及答案

牛津译林版五年级英语(下册)期末检测及答案(满分:100分时间:60分钟)一、从下列每组单词中选出不同类的一项。
(10分)1、()A.old B.wash C.kind2.()A.Monday B.Friday C.salad 3.()A.clever B.read C.play4.()A.hot B.sweet C.weekend 5.()A.tea B.watch C.do二、选出下列每组中单词画线部分发音不同的一项。
(10分)1、()A.three B.thin C.that2.()A.clean B.clever C.uncle 3.()A.drink B.think C.long 4.()A.where B.who C.which 5.()A.school B.March C.teacher三、选择填空。
(20分)1、—Who's that woman? ()—_______is my mother.A.She B.He C.It 2、—What's the weather like today? ()—It’s ______.A.rain B.rains C.rainy3、It's cold________ Beijing. ()A.on B.at C.in4、—Who' s that man? ()—________A.She's my dad. B.He’s my father. C.He's my sister.5、________ your favourite season? ()A.What B.What's C.Why6、It’s time ______ go home. ()A.to B.for C.on7、This is __________________duck. ()A.my B.an C.you8、We have _________ art room. ()A.a B.an C./9、I'll go to the zoo ________ Sunday. ()A.in B.on C.at10、—Do you like tea? ()—_________A.No, he doesn’t. B.Yes, I do. C.Yes, I am. 四、用括号中所给单词的恰当形式补全句子。
牛津译林版五年级英语(下册)期末综合能力测试卷及答案

牛津译林版五年级英语(下册)期末综合能力测试卷及答案(满分:100分时间:60分钟)一、从下列每组单词中选出不同类的一项。
(10分)1、()A.restaurant B.library C.heavy2.()A.wrote B.get C.told3.()A.ask B.try C.moon 4.()A.July B.telephone C.television 5.()A.when B.east C.west二、选出下列每组中单词画线部分发音不同的一项。
(10分)1、()A.chair B.come C.child 2.()A.cold B.coffee C.pencil 3.()A.nice B.cake C.coat 4.()A.doctor B.cousin C.dance 5.()A.class B.cup C.juice三、选择填空。
(20分)1、—What's the weather like today? ()—It’s ______.A.rain B.rains C.rainy2、_________favourite food is ice cream. ()A.He B.She C.Her3、—What's your ________ job? ()—________ a cook.A.mother; She's B.brother's; He's C.mother's; She 4、Look ________the blackboard. ()A.in B.on C.at5、—________ are you going? ()—I’m going to the cinema.A.What B.When C.Where 6、—What’s your sister _____? ()—She is thin. She _____ reading books.A.like; likes B.likes; like C.like; like7、I like to __________ on Saturday. ()A.play piano B.play the football C.play the piano 8、My grandmother likes apples, because they are ______. ()A.hot B.healthy C.thirsty9、What do you do ________ Sundays? ()A.in B.on C.at 10、—Would you like ________?()—Yes, it’s healthy.A.any milk B.some milk C.a milk四、用所给单词的适当形式填空。
牛津译林版五年级英语(下册)期末达标试题及答案
牛津译林版五年级英语(下册)期末达标试题及答案(满分:100分时间:60分钟)一、从下列每组单词中选出不同类的一项。
(10分)1、()A.often B.sleep C.sometimes 2.()A.cook B.pick C.weekend 3.()A.holiday B.Teachers’DayC.May Day 4.()A.Monday B.June C.March 5.()A.March B.autumn C.August二、选出下列每组中单词画线部分发音不同的一项。
(10分)1、()A.snow B.yellow C.down 2.()A.tea B.bread C.sea3.()A.he B.she C.egg 4.()A.bye B.windy C.sunny 5.()A.cow B.how C.snow三、选择填空。
(20分)1、—What are ________ going to do? ()—They are going to listen to music.A.we B.you C.they2、February is the __________ month of a year.()A.second B.two C.three3、—Can I take a picture _______ the mountain? ()—Yes, you can.A.to B.of C.at4、There isn’t water in the river. ()A.some B.a C.any5、My mother is a teacher. She goes to school ___ 7:00 ___ the morning.()A.at; on B.at; at C.at; in6、It’s time___________ breakfast. ()A.for B.of C.to7、________ are my shoes. ()A.This B.That C.Those8、Here _______ a glass of _______ for you. ()A.is; juices B.is; juice C.are; juice9、It’s too ______. I don’t like it. ()A.fresh B.hot C.delicious10、I often plant flowers _______ my grandpa. ()A.and B.with C.or四、用所给的适当形式填空。
牛津译林版五年级英语(下册)期末模拟试卷及答案
牛津译林版五年级英语(下册)期末模拟试卷及答案题序一二三四五六七八九十总分得分(满分:100分时间:60分钟)(听力部分40分)一、听录音,选出你所听到的单词,听两遍。
(10分)( ) 1. A.cow B.slow C.snow( ) 2. A.tea B.salad C.beef( ) 3. A.sandwiches B.vegetable C.hamburgers ( ) 4. A.hot B.delicious C.sweet( ) 5. A.drink B.food C.juice二、听录音,选择正确的图片,读两遍。
(10分)( ) 1. A.B.( ) 2. A.B.( ) 3. A.B.( ) 4. A. B.( ) 5. A.B.三、听录音,选择正确的答语,读两遍。
(10分)( ) 1. A.Yes, I’m okay. B.Sure.( ) 2. A.Yes, please. B.I’m hungry.( ) 3. A.He is reading. B.She is sleeping.( ) 4. A.It’s about 2000 years old. B.That’s old.( ) 5. A.The girl is talking. B.That’s a woman.四、听录音,根据所听内容补全短文,听两遍。
(10分)Alice is my _________. She’s from Canada, but she _________ in China now. Her father is a _________. He teaches _________. Her mother is a factory _________. She makes cars. Alice is a student. She likes _________ and reading. She _________ goes to the _________. She often _________ her grandparents at weekends. They_________ picnics in the park.(笔试部分60分)五、单项选择,将正确答案序号填在括号里。
牛津译林版五年级英语(下册)期末精编试卷及答案
牛津译林版五年级英语(下册)期末精编试卷及答案(满分:100分时间:60分钟)一、从下列每组单词中选出不同类的一项。
(10分)1、()A.mountain B.hill C.house2.()A.shy B.speak C.young 3.()A.hot B.sweet C.hamburger 4.()A.swim B.salad C.dance 5.()A.Thursday B.Sunday C.hard-working二、选出下列每组中单词画线部分发音不同的一项。
(10分)1、()A.us B.busy C.study 2.()A.hear B.dear C.early 3.()A.clean B.eat C.bread 4.()A.answer B.after C.parent 5.()A.library B.behind C.river三、选择填空。
(20分)1、This is ______ book. That is ______. ()A.my; yours B.mine; yours C.my; your2、I have breakfast _____ six thirty _____ the morning.()A.on; in B.at; on C.at; in3、I often do my homework _______ weekends. ()A.in B.on C.of4、This is ____ you. ()A.four B.to C.for5、I have ____________ English book. ()A.a B.an6、Are these ________? ()A.you B.your C.yours7、Please send an email _______ Sarah. ()A.from B.to C.for8、I’m ______. I’d like some tea. ()A.hungry B.thirsty C.full9、We ________ tea in the afternoon and watched TV. ()A.drink B.drank C.drinked10、There ________ four boys in the playground. ()A.is B.are C.am四、所给词的适当形式填空。
牛津译林版五年级英语(下册)期末摸底测试及答案
牛津译林版五年级英语(下册)期末摸底测试及答案(满分:100分时间:60分钟)一、从下列每组单词中选出不同类的一项。
(10分)1、()A.April B.month C.August2.()A.mine B.theirs C.her3.()A.morning B.eating C.listening 4.()A.third B.tenth C.three5.()A.summer B.season C.spring二、选出下列每组中单词画线部分发音不同的一项。
(10分)1、()A.good B.football. C.noodles2.()A.flower B.window C.cow3.()A.fly B.windy C.sorry4.()A.eat B.meat C.head5.()A.house B.mouse C.cousin三、选择填空。
(20分)1、—________ season do you like best? ()—Spring.A.Why B.How C.Which2、_____ book is in the classroom. _____ is here. ()A.Mine;Your B.My;Your C.My;Yours3、Let’s _________ a birthday card for our mother. ()A.make B.making C.makes4、It’s time ______ go to school. ()A.to B.at C.for5、Tree Planting Day is ______ March. ( )A.at B.on C.in6、—What are ________ going to do? ()—They are going to listen to music.A.we B.you C.they7、His family ________ a big family. ()A.are B.am C.is8、—______do you like spring best? ()—Because the weather is nice.A.Which B.Why C.What9、________ are my shoes. ()A.This B.That C.Those10、There are some special days _____ April. ()A.in B.on C.at四、用所给词的适当形式填空。
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五年级下英语期末模拟测试卷8带解析1.找出不同类的单词(10分)()(1)A.fly B.jump C.walk Dlimber()(2)Aat B.monkey C.zoo D.panda()(3)A.head B.nose C.ear D.mom()(4)A.march B.spring C.summer D.winter()(5)A.tofu Babbage C.trunk D.eggplant()(6)Aool Bold C.skate D.hot()(7)A.season B.summer C.fall D.winter()(8)Aloud B.snow C.rain D.spring()(9)A.always B.swim C.skate D.sleep()(10)A.evening B.work C.noon D.morning2.从方框中选择适当的词填空(6分)hat why which who where when(1)________ do you get up? At 6:00(2)________is zip’s favorite season?(3)________is your art teacher?(4)________are you from? I’m from china.(5)________do you like winter? Because Ican skate. 3.what are the elephants doing ?________ drinkingA.we’reB.They’reC.It’s4.Can tigers swim?--- ________.A.Yes they can’tB.No,they can’tC.No, they can 5.Can I speak to your mom,Please? ________ ________A.SureB.Thank youC.You are wele6.hat is your father doing? _____walking.A.It’sB.He’sC.She’s7.--hat’s he like !----_____________A.He likes teaB.He is shortC.r Carter8.Is there a mirror in the house?A.Yes there isB.Yes it isC.Yes there are9.连词成句,注意大小写以及标点(10分)(1)see I elephants two(.)___________________________________________________(2)hat park big a nature(!)___________________________________________________(3)you is for a there call(.)___________________________________________________(4)an in study the writing e-mail he’s(.)___________________________________________________(5)in evening eat dinner I 7:00 the at(.)___________________________________________________10.照样子,写出下列单词的ing形式(6分)11.根据自身情况完成下列问题(6分)(1)hen do you get up ?___________________________________________________(2)hat do you do on the weekend?________________(3)hich season do you like best?_________________(4)hen is your birthday?_____________________(5)hen is your mother’s birthday?___________________(6)hen do you go to school?________________________12.完成下列句子。
(1)Are you eating lunch? No,___________.(2)Is he playing chess? Yes,_________________.(3)y birthday is _____________________.(10月1日)(4)He is _____________________________(接电话)(5)I usually _______________________at 5:00.(晨练)(6)hat is it doing? It is ___________________.(跳)13.阅读理解(10分)I like my village .There are many mountains near my village.There is a river in front of my village.The village is very beautiful in spring. The mountains e green. There are many trees and flowers.The flowers are colourful .There are many ducks in the clean river. any fish swim happyily in the river. But I like summer. it’s not hot .It’s very cool .Do you like my village? ele ty village.(一)根据对话内容回答问题(1)Is there a river in the village?___________________________(2)Are there many fish in the river?___________________________(3)hich season does she like best?____________________________(4)hich season is beautiful?__________________________________(5)Do you like the village?____________________________________(二)根据对话内容进行判断正误,正确的用“√”,错误的用“×”表示。
( )(1)There are many houses on the mountain.( )(2)The summer is colorful.( )(3)It’s not hot in summer.( )(4)There are many fish in the river.( )(5)any ducks are in river in spring完成下列句子。
参考答案1.(1)D (2)C (3)D (4)A (5)C (6)C (7)A (8)D (9)A (10)B【解析】2.(1)when (2)which (3)who (4)where (5)why【解析】3.B【解析】主语the elephants 为复数主语,因此用they来代替,系动词be是are,可以写成缩写They’re4.B【解析】can的一般疑问句,否定会用No,主语+can’t5.A【解析】Can I speak to your mom,Please? 我可以和你的妈妈说吗,是礼貌用语,应该用Sure来回答6.B【解析】主语是your father 男士用人称代词he7.B【解析】be +like 结构是询问人的外貌长相8.A【解析】Is there 的一般疑问句,肯定回答是Yes there is9.(1)I see two elephants .(2)hat a big nature park !(3)There is a call for you .(4)He is writing an e-mail in the study.(5)I eat dinner at 7:00 in the evening.【解析】10.swimming playing the piano running writing a letter taking picture skating【解析】11.(1)I get up at 7 o’clock.(2)I play football .(3)I like fall best.(4)It’s 10st ctober.(5)It’s 25st ctober.(6)hen do you go to school? At 8 o’clock.【解析】12.(1)I am not (2)he is (3)1st ctober. (4)on the phone (5)exercise (6)jumping【解析】(1)I am not 一般疑问句的否定回答,问句主语是you,be动词时are,答语对应的主语是I,对应am(2)he is一般疑问句的肯定回答,问句主语是he,be动词时is,答语对应的主语是he,对应is(3)1st ctober. 英语里面的日期表达方式,先写日,用序数词,后写月(4)on the phone 固定短语(5)exercise 锻炼(6)jumping 现在进行时态,所以用动词的现在分词形式13.(一)(1)Yes, there is. (2)Yes,there are. (3)Summer (4)Spring (5)Yes,I do.(二)(1)×(2)×(3)√(4)√(5)√【解析】的导线要比原线圈粗,C 错误;居民小区各个用电器都是并联的,它们的电流总和等于副线圈中的电流,故D 错误.【答案】AB11.如图所示,发电机内部线圈处于磁铁和圆柱形铁心之间的径向磁场中,两半边间的过渡区域宽度很小,可忽略不计.线圈的总匝数为N、总电阻为r,每匝线圈的面积为S,线圈所在位置的磁感应强度大小为B.当线圈以角速度ω匀速转动时,额定电压为U、电阻为R的小灯泡在电路中恰能正常发光,则发电机产生的感应电动势的有效值是( )2A.NBSω B.NBSω2rUC.U D.1+R【解析】根据题述线圈处于磁铁和圆柱形铁心之间的径向磁场中,当线圈以角速度ω匀速转动时,产生的交变电流为矩形波,发电机产生的感应电动势的有效值是 NBSω,选项 A 正确,B 错误.由闭Ur r 合电路欧姆定律,E =U + R =1+RU ,选项C 错误,D 正确.【答案】 AD12. 如图所示,为探究理想变压器原、副线圈电压、电流的关系,将原线圈接到电压有效值不变的正弦交流电源上,副线圈连接相同的灯泡L 、L ,电路中分别接了理想交流电压表 V 、V 和理想交流电流表A 、A ,导线电阻不计,如图所示.当开关S 闭合后()A .A 示数变大,A 与A 示数的比值不变B .A 示数变大,A 与A 示数的比值变大C. V 示数变小,V 与 V 示数的比值变大D. V 示数不变,V 与V 示数的比值不变U n 【解析】 由U =n 知,开关 S 闭合后,V 示数不变,V 与 V 示 2 2数的比值不变,故选项 C 错误,选项 D 正确;开关 S 闭合后,副线圈U I n 闭合回路的总电阻R 减小,由 I = R 知,I 变大,由I 2=n 1知,A 示数变大,且A 与A 示数的比值不变,故选项A 正确.【答案】 AD第Ⅱ卷(非选择题 共 52 分)二、实验题(本题有 2 小题,共 15 分,请将答案写在题中的横线上)13.(6 分)为了测定和描绘“220 V 40 W”白炽电灯灯丝的伏安特性曲线,可以利用调压变压器供电.调压变压器是一种自耦变压器,它只有一组线圈 L ,绕在闭合的环形铁芯上,输入端接在 220 V 交流电源的火线与零线间,输出端有一个滑动触头 P ,移动它的位置,就可以使输出电压在 0~250 V 之间连续变化,图中画出的是调压变压器的电路图符号.实验室内备有交流电压表、交流电流表、滑动变阻器、开关、导线等实验器材.(1)在图中完成实验电路图.(2)说明按你的实验电路图进行测量,如果电表内阻的影响不能忽略,在电压较高段与电压较低段相比较,_ 段的误差更大,因为.【解析】(1)如图所示.开关应安在火线一边.(2)如果采用电流表外接法,电压较高段误差更大,因为电压越高,灯丝电阻越大,由于电压表分流而造成的误差越大;如果采用电流表内接法,电压较低段误差更大,因为电压越小,灯丝电阻越小,由于电流表分压造成的误差越大.【答案】见解析14.(9 分)有一个教学用的可拆变压器,如图甲所示.它有两个外观基本相同的线圈A、B,线圈外部还可以绕线.(1)某同学用一多用电表的同一欧姆挡先后测量了A、B 线圈的电阻值,指针分别对应图乙中的a、b 位置,由此可推断线圈的匝数较多(选填“A”或“B”).(2)如果把它看成理想变压器,现要测量A 线圈的匝数,提供的器材有,一根足够长的绝缘导线、一只多用电表和低压交流电源.请简要叙述实验的步骤(写出要测的物理量,并用字母表示).___A 线圈的匝数为n=_ .(用所测物理量符号表示)A【解析】 (1)由图乙可知a 位置的阻值大于 b 位置的阻值,由电阻定律可得A 线圈的匝数多于B 线圈的匝数.(2)①用长导线绕一个 n 匝线圈,作为副线圈替代A 线圈.②把低压电源接B 线圈,测得线圈的输出电压U.U A ③用A 线圈换下绕制的线圈测得A 线圈输出电压U A .n A = Un U A 【答案】 (1)A (2)步骤见解析 n A = Un 三、计算题(本题有 3 小题,共 37 分,解答应写出必要的文字说明﹑方程式和重要的演算步骤,只写出最后答案的不能得分,有数值计算的题,答案中必须明确写出数值和单位)15.(10 分)如图甲所示,在周期性变化的匀强磁场区域内有垂直于磁场的半径为 r =1 m 、电阻为 R =3.14 Ω 的金属圆形线框,当磁场按图乙所示规律变化时,线框中有感应电流产生.(1)在图丙中画出感应电流随时间变化的i-t 图象(以逆时针方向为正);(2)求出线框中感应电流的有效值.【解析】(1)如图所示.(2)设电流的有效值为I,则有2 2 T22TI RT=i R·3+i R3得I= 2 A【答案】(1)见解析(2) 2 A 16.(13 分)如图所示,匀强磁场磁感应强度B=0.5 T,匝数为n=50匝的矩形线圈,绕垂直于匀强磁场的转轴OO′匀速转动,每匝线圈长为L=25 cm,宽为d=20 cm.线圈每分钟转动1 500 转,在匀速转动过程中,从线圈平面经过图示位置时开始计时.(1)写出感应电动势e 的瞬时值表达式;(2)若每匝线圈本身电阻r=0.02 Ω,外接一阻值为13 Ω的用电器,使线圈与外电路组成闭合电路,写出感应电流i 的瞬时值表达式;(3)若从线圈平面垂直于磁感线的位置开始计时,感应电动势e′和感应电流i′的瞬时值表达式如何?(4)画出(1)(2)中的e-t、i-t 图象.【解析】(1)线圈匝数n=50,磁场的磁感应强度B=0.5 T,线1 500圈转动的角速度ω=2πf=2π×rad/s=50π rad/s,线圈的面积S=60Ld=0.05 m2I 所以 E m =nBS ω=50×0.5×0.05×50π V ≈196 V从图示位置计时,有 e =E m c osωt =196cos(50πt) V.(2)若 r =0.02 Ω,则 r′=50 r =0.02×50 Ω=1 ΩR 总 =R +r′=13 Ω+1 Ω=14 ΩE m 196 m R = 14 A =14 A总所以 i =I m c osωt =14cos(50πt) A(3) 若从线圈平面与磁感线垂直的位置开始计时,即从中性面开始计时,感应电动势和感应电流的瞬时值表达式分别为e′=196sin(50πt)V ,i′=14sin(50πt) A.(4) 因为 ω=50π,2π 所以T = ω=0.04 s ,E m =196 V ,I m =14 A (1)(2)中的 e -t 、i -t 图象分别如图甲、乙所示.【答案】见解析17.(14 分)一台小型发电机的最大输出功率为100 kW,输出电压恒为500 V,现用电阻率为1.8×10-8 Ω·m,横截面积为10-5 m2 的输电线向4×103 m 远处的用户输电,要使发电机满负荷运行时,输电线上的损失功率不超过发电机总功率的4%,求:(1)所用的理想升压变压器原、副线圈的匝数比是多少?(2)如果用户用电器的额定电压为220 V,那么所用的理想降压变压器原、副线圈的匝数比是多少?(3)想一想,当深夜接入电路的用电器减少时,用电器两端的电压是大于、小于还是等于220 V?若用电器电路中电流为100 A,求此时用电器两端的电压数值.2l=【解析】(1)输电要用两根导线,则输电线的电阻为r=ρS 2×4×1031.8×10-8×Ω=14.4 Ω10-52 P 2 由题意知P 损=P×4%=U 2r 105105×0.04= 2 2×14.4U =6 000 Vn U 500 1 升压变压器原、副线圈匝数比n =U =6 000=12. 2 2P 10550 (2)I =U =6×103 A = 3A 50 U 损=I ·r = 3×14.4 V =240 V 而U =U -U 损=6 000 V -240 V =5 760 Vn U 5 760 288 n =U = 220 = 11 4 4 降压变压器原、副线圈匝数比为 288 11(3)用电器总数减少时,用电器两端电压将增大由题知 I ′=100 A 则由I 4′n 288 4 I ′=n = 11U所以 I ′ 1 3 =U 损 ′=I ′·r 3= 288 ×1 1 4.4 V =55 V 而U 1、U 2 不变U 3′=U 2-U 损′=(6 000-55) V =5 945 VU 3′ n 3 U ′ n = , 4 4U ′ n 4 11 4 = ×U ′= ×5 945 V≈227 V. n 3 3 28【答案】 (1)1 :12 (2)288 :11 (3)大于 220 V 227 V。