人教版四年级英语期末复习试卷
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人教版四年级下册英语期末试卷(含答案)一、听力部分(共30分)听录音,选出你所听到的单词或短语。
每个单词或短语读两遍。
(每小题1分)1. A. apple B. banana C. carrot2. A. cat B. dog C. rabbit3. A. teacher B. doctor C. dentist4. A. happy B. sad C. angry5. A. run B. jump C. swim答案:1. B2. C3. A4. A5. C听录音,选择正确的答案。
每段对话或问句读两遍。
(每小题1分)6. A. Basketball. B. Football. C. Tennis.What's your favorite sport?7. A. I want a red one. B. I have a green one. C. I like blue.What color do you like?8. A. Yes, it is. B. No, it isn't. C. It's a rabbit.Is that your dog?9. A. Good idea! B. Thank you. C. Yes, I do.Let's go to the park.10. A. She is my sister. B. He is my brother. C. Yes, they are.Are they your parents?答案:6. C7. B8. B9. A10. B听录音,补全对话。
(每小题1分)11. A: What day is it today? B: It's ___________.A: Is it Saturday today? B: ___________.12. A: What's your favorite ___________? B: I like ___________.A: ___________ do you like? B: I like red.13. A: Look at the bird. What color is it? B: It's ___________.A: Is that a blue bird? B: No, ___________.14. A: Let's ___________ basketball. B: OK! I like___________.A: Let's play ___________ the park. B: That sounds fun.15. A: Can you ___________ a story? B: Yes, ________, please.A: ___________ birds in the tree. B: That's a nice story.答案:11. Sunday, No12. color, blue, What color13. yellow, it isn't14. play, basketball, at15. tell, tell, I see。
【精品】人教版小学英语四年级上册期末考卷(考试时间:90分钟,满分:100分)一、听力理解(共10题,每题2分,总分20分)1. 听录音,选择正确的图片。
2. 听录音,选择正确的单词。
3. 听录音,选择正确的句子。
4. 听录音,判断对错。
5. 听录音,选择正确的答案。
6. 听录音,填空。
7. 听录音,回答问题。
8. 听录音,选择正确的图片。
9. 听录音,选择正确的单词。
10. 听录音,选择正确的句子。
二、词汇选择(共10题,每题2分,总分20分)1. A. good B. bad C. happy D. sad2. A. apple B. banana C. orange D. pear3. A. cat B. dog C. elephant D. tiger4. A. read B. write C. play D. draw5. A. one B. two C. three D. four6. A. red B. blue C. green D. yellow7. A. morning B. afternoon C. evening D. night8. A. hot B. cold C. warm D. cool9. A. happy B. sad C. angry D. tired10. A. big B. small C. tall D. short三、语法填空(共10题,每题2分,总分20分)1. I have a ___________.2. She is ___________.3. They are ___________.4. This is a ___________.5. That is a ___________.6. It is ___________.7. We are ___________.8. You are ___________.9. He is ___________.10. She is ___________.四、阅读理解(共5题,每题4分,总分20分)阅读下面的短文,然后回答问题。
PEP人教版四年级上册英语测试题测试题人教版小学英语人教PEP四年级英语第一学期期末复习卷五1.听录音,选择,勾出正确的答案。
(10分)2.听录音,判断对错,打√ 或打×。
(10分)3.听音圈出听到的内容。
(10分)(1)Let me clean the door / desk.(2)Where is the fridge / friend?(3)Look! They are on the shelf / sofa.(4)Pass me the plate / fork, please.(5)Is she in the kitchen / chicken?4.听一听,连一连,把Amy 去过的地方连起来。
(10分)5.听一听,填出所缺的阿拉伯数字或单词。
(10分)(1)11+()=54(2)13+ 22=()(3)()+ 10 = 45(4)A:What’s in your _______?B: There are 4________.(5)A:Have some _______,please.B: No, thanks. I like ______ and _________.(6)A: What’s your _______?B: He’s a ________.6.听音连线。
( 10分)7.听问句,选答句。
(10分)(1)A. Yes , you do .B.Yes, I do.C.Yes. Pass me a plate,please.(2)A. Wait and see.B. I’d like some soup.C.Sure.Here you are.(3)A. He’s a teacher.B. She’s a teacher.C. He’s tall.B. Yes,she is.C. Yes,he is .(5)A. She’s a cat.B. Is she in the living room?C. Hey, your cat!8.根据语篇及图片填写单词。
20232024学年全国小学四年级上英语人教版期末考试试卷一、听力部分(20分)1. 听录音,选出你听到的单词。
(5分)(1)A. cat B. dog C. bird(2)A. book B. pen C. pencil(3)A. red B. blue C. green(4)A. big B. small C. tall(5)A. happy B. sad C. tired2. 听录音,选出你听到的句子。
(5分)(1)A. How are you? B. How old are you? C. What's your name?(2)A. I'm seven. B. I'm eight. C. I'm nine.(3)A. My name is Tom. B. My name is Mary. C. My name is John.(4)A. I like apples. B. I like bananas. C. I like oranges.(5)A. He is my father. B. She is my mother. C. They are my friends.3. 听录音,判断正误。
(5分)(1)It's a sunny day. ()(2)The girl is wearing a red dress. ()(3)The boy has a black cat. ()(4)They are playing football. ()(5)She is reading a book. ()4. 听录音,填空。
(5分)(1)I have a _______.(2)She is _______ years old.(3)The book is _______.(4)He is my _______.(5)They are _______.二、阅读理解(30分)1. 阅读短文,选择正确答案。
新人教版四年级上册《英语》期末试卷及答案一、选择题(每题2分,共20分)1. Which sentence is correct?A. I like apples and pears.B. I like apples, pears.C. I like apples, apples.D. I like apple and pear.答案:A2. Which word is different from the others?A. catB. dogC. fishD. bird答案:C3. Which sentence is correct?A. I have two books and three pencils.B. I have two books, three pencils.C. I have two books; three pencils.D. I have two books, and three pencils. 答案:A4. What time is it?A. It's time for dinner.B. It's 6:00 p.m.C. It's time to go to school.D. It's 7:00 a.m.答案:B5. Which sentence is correct?A. I can swim and ride a bike.B. I can swim, ride a bike.C. I can swim; ride a bike.D. I can swim, and ride a bike.答案:A6. Which word is different from the others?A. motherB. fatherC. brotherD. teacher答案:D7. Which sentence is correct?A. There are four books on the table.B. There is four books on the table.C. There are four books in the table.D. There is four books on the table.答案:A8. Which sentence is correct?A. What color is your favorite?B. What is your favorite color?C. Which color is your favorite?D. What color do you like best?答案:B9. Which sentence is correct?A. I have a blue car and a yellow bike.B. I have a blue car, a yellow bike.C. I have a blue car; a yellow bike.D. I have a blue car, and a yellow bike. 答案:A10. Which sentence is correct?A. My mother is a doctor.B. My mother is doctor.C. My mother is a doctor,D. My mother is doctors.答案:A二、填空题(每题2分,共20分)1. My name is ___. I am a ___.答案:Your Name, Student2. I have ___ apples and ___ oranges.答案:Four, Three3. The ___ is yellow and the ___ is red.答案:cat, bird4. ___ are my favorite fruits.答案:Apples5. There are ___ people in my family.答案:Five6. I can ___ and ___.答案:swim, ride a bike7. It's ___ o'clock in the morning.答案:seven8. My mother is a ___.答案:doctor9. I go to ___ by ___.答案:school, bus10. ___ colors do you like?答案:What三、翻译题(每题5分,共25分)1. 我有一个红色的铅笔和一个蓝色的铅笔。
人教版小学四年级英语上册期末综合复习试卷及答案一、读一读,选出与所给单词画线部分发音相同的一项1. cat Sam makes a cake.________2. fine His father likes him very much.________3. nose The rose is not on sale. ________4. excuse The cute duck is very fun.________5. she Please let the boy help me.________二、选出与所给单词同类的一项。
() 1. bowl A. chopsticks B. sofa C. shoes() 2. cook A. cousin B. nurse C. uncle() 3. study A. soup B. fork C. bedroom() 4. phone A. fan B. teacher C. student() 5. candy A. hair B. snack C. horse三、根据图片及首字母提示补全单词。
四、情景交际。
()1. 你想知道朋友书包里有什么,你可以问:A. What‘s in your schoolbag?B. Where is your schoolbag?C. What colour is your schoolbag?()2. 当你介绍你的朋友给大家认识时,你可以说:A. My friend is tall.B. This is my friend.C. I have a friend.()3. 你想知道钥匙在哪里,你可以这样问:A. Are these keys?B. Where is the key?C. Is it a key?A. What‘s your father‘s job?B. Who is he?C. Is this your father?()5. 你想知道晚餐吃什么,你可以问:A. What would you like for dinner?B. Would you like some beef for dinner?C. What‘s for dinner?五、单项选择。
人教版2022--2023学年度第一学期期末测试卷四年级 英语本试卷总分100分,考试时间40分钟。
听力部分一、听录音,选出你所听到的单词或词组,并将其字母代号填入题前括号内。
注意每小题听三遍。
(共10小题,每小题1分,满分10分) ( ) 1. A. toy B. key C. cute ( ) 2. A. bowl B. wow C. wall ( ) 3. A. blue bag B. brown shoes C. blue glasses ( ) 4. A. hair B. hat C. her ( ) 5. A. bed B. red C. find ( ) 6. A. strong B. quiet C. shoe ( ) 7. A. spoon B. soup C. pass ( ) 8. A. so muchB. how manyC. how much ( ) 9. A. English book B. Chinese book C. storybook ( ) 10. A. cakeB. faceC. make二、听录音,选出你所听到的句子,并将其字母代号填入题前括号内。
注意每小题听三遍。
(共10小题,每小题2分,满分20分) ( ) 11. A. His name is Zhang Peng. B. His name is John. C. Her name is Sarah.( ) 12. A. Is she in the kitchen? B.Is he in the study? C. Is she in the bedroom?( ) 13. A. He is tall and thin. B. She is short and thin. C. He has short hair.( ) 14. A. It’s under the desk. B. It’s under the chair. C. It’s near the desk.( ) 15. A. Would you like some beef? B. What would you like? C. Would you like some chicken? ( ) 16. A. My cousin is a student. B. My aunt is a cook. C. My uncle is a teacher.( ) 17. A. I have a new schoolbag. B. I have a new ruler. C. I have a new pencil.( ) 18. A. Is this your uncle, Sarah? B. Is this your father, Lily? C. Is this your sister, Tim?( ) 19. A. The sofa is in the living room. B. The table is in the living room.……○………………内………………○………………装………………○………………订………………○………………线………………○…此卷只装订不密封……○………………外………………○………………装………………○………………订………………○………………线………………○…C. The phone is on the table.( ) 20. A. Turn on the light.B. Close the window.C. Clean the blackboard.三、听录音,选出与句子内容相关的图画,并将其字母代号填入题前括号内。
小学英语四年级下册期末考试(时间:60分钟 总分100分)听力部分(60%)一、听录音,给下列单词标序号。
将数字写在单词前的横线上。
(8%) dinner little work nurse homework card tall farm 二、听句子,圈出你所听内容的编号。
(8%)班级___________ 座位号………线…………内…………不…………要…………答…………题………………………三、听对话,判断所听内容与图片是“√”否“×”相符。
(5%)四、听对话,判断所听内容与下列句意是“√”否“×”相符。
(10%)()1.The library is on the first floor.()2.It’s windy and rainy in Sydney.()3.Those are horses.()4.Linda’s shoes are green.()5.Sarah’s skirt is $89.五、听对话,在图片下写上相应的时刻。
(10%)英语英语英语 2六、听对话,用数字给下列句子标号。
(答案1已给出)(7%)()You can try them on.( 1 )Can I help you?()Yes.The pants are nice.()Here you are.()Thank you.I love the orange pants.()They are just right.How much are they?()Ok.I’ll take them.()They are $85.七、听短文,将单词的编号写在右边功能室位置图中的相应方框内。
(4%)英语英语英语 3英语 英语 英语4八、听短文,在框内圈出你所听到的单词。
(8%)Hello!This is farm.These are .They are .are green beans.Look at the .I haveThey are .I have dogs on the farm.笔试部分(40%)一、请从方框内圈出下列物品的英文单词(有一个单词是多余的),并按单词首字母A-Z 的排序法,将所圈单词抄在相应四线三格内。
一、单项选择1.—Let’s draw some pictures here. ( )—_______!A.Good idea B.Well done C.What a pity 2.—What’s the matter? Are you ill? ( )—Yes, I have ______ cough and _______ headache.A.a; a B.a; / C./; /3.I’m thirsty. I want ________. ( )A.to eat a pie B.drink some water C.to drink some water 4.—What’s the matter with _______ ? ( )—He is ill.A.he B.his C.him5.The girl _______ a red dress is my good friend. ( )A.in B.with C.on6.—I’m very _______. ( )—Here’s a fan _______ you.A.cold; for B.hot; for C.cold; to7.He can’t ________ them, his hands ________. ( )A.draws; hurt B.draw; hurts C.draw; hurt 8.—Who’s the king of all the animals? ( )—________.A.The apple B.The tiger C.Mr Wang9.—_______ subjects do you have this term? ( )—Eleven.A.What B.How much C.How many10._______ is the first season of a year. ( )A.Spring B.Sunday C.Summer11.It's nine o'clock in the evening. It's time _________ bed. ( )A.to B.in C.for12.Ouch! I can't run now. My foot _________. ( )A.big B.small C.hurts13.—I can’t swim. ( )—I can’t swim _______.A.too B.two C.either14.Here ______ a lot of beautiful flowers. ( )A.are B.am C.is15.I ______ a bag. He ______ a bag, too. ( )A.have; has B.have; have C.has; have二、用单词的适当形式填空16.Here _______ (be) some banana juice.17.It’s time to have a ______ (draw) lesson.18.The women in red _______ (be) our teachers.19.I don’t have ______ (some) stickers.20.—Whose _______ (box) are they? —They’re _______ (Miss Li). 21.Look at these _______ (boat) on the river! Let’s go _______ (boat). 22.—What’s the matter with _______ (she)?—She _______ (be) ill. 23.—Whose ______ (毛衣) are these? —They’re Tim’s.24.Mike ________ (have) a ________ (swim) lesson on Sunday. 25.Look at _____ (we) fruit salad.26.Mary can _____ (have) lunch at school every day.27.What a lovely day it is! Let's go _____ (boat) in the lake. 28.This is _____ (we) new timetable for today.29.The teacher's office is on the ________ (two) floor.30.It’s cool and ______ (rain).三、完成句子31.—What’s the m______ with you?—I’m ill. I have a headache.32.完成对话,每空一词。
第二学期期末考试试卷 四年级英语试卷 时间:40分钟 满分:100分 听力部分(共60分) 一、听录音,按所听内容,选择正确的图片。
每小题读两遍。
(本题5小题,每小题2分,共计10分) 1.( ) A. B. 2.( ) A. B. 3.( ) A. B. 4.( ) A. B. 姓名 班级___________ 座位号……订…………线…………内…………不…………要…………答…………题………………………5.() A. B.二、听录音,选出你所听到的单词。
每小题读两遍。
(本题5小题,每小题2分,共计10分)()1.A.library B.lunch()2.A.nurse B.birth()3.A.windy B.cloudy()4.A.potato B.tomato()5.A.cute B.pretty三、听录音,根据所听短语的顺序给下列图片标序号。
每小题读两遍。
(本题5小题,每小题2分,共计10分)( ) ( ) ( ) ( ) ( )四、听录音,判断图片与所听到的内容是否相符,一致的画“√”,不一致的画“×”。
每小题读两遍。
(本题5小题,每小题2分,共计10分)五、听录音,选出你所听到的句子。
每小题读两遍。
(本题5小题,每小题2分,共计10分)()1.A.These are John’s gloves. B.These are John’s shoes.()2.A.It’s time for breakfast. B.It’s time for lunch.()3.A.They’re very cheap. B.They’re very expensive.()4. A.It’s cool in Beijing today. B.It’s warm in Bejing today.()5.A.My sweater is green. B.My jacket is green.六、听短文,选择正确图片,将序号填在横线上。
2012年人教版四年级英语期末复习试卷一.选出不同类的单词.(10%)( )1. A.teacher B. fanther C. brother D. mom( )2 k B. water C. soup D. coffee( )3. A.kitchen B. bathroom C. classroom D. study( )4.A. driver B. doctor C.nurse D. music( )5.A. thin B. tall C. eye D. short( )6.A. noodles B. chopsticks C.spoon D. plate( )7. A. phone B. fork Cfridge ( )8. A. window B. math book C.door D. floor( )9. A. science B.schoolbag C. sports D. painting( )10.A.vegetable B.jucie C.hamburger D. beef二. 读句子,给图标序号. (5%)( ) ( ) ()()()――ike. Please put up the picture. ――!Look.He is my friend. He is so strong. He has short black hair and big eyesThis is my bedroom. You can see a bed , a puter a desk and a chair.y family has 4 members.y father.my mother ,me and my little puppy.y uncle is a driver.三.选择正确的答句(10%)( )1.Are they in the living room? A. Yes, he is.( )2.Is this your father? B. I’d like some chicken. ( )3. hat’s his name? C. No, they aren’t.( )4. Can I have some noodles? D. His name is ike.( )5. hat would you like for dinner? E. Sure. Here you are.四.看图片,补全单词(18%)He’s a tall b _ _.I can see a d_ _ _ in the picture.I’d like some f_ _ _ and r_ _ _ .y uncle is a f_ _ _ _ _.ele to our s_ _ _ _ _.This is a d_ _ _.y f_ _ _ _ _ is a d_ _ _ _ _.(1)(2)(3)(4)(5)(6)(7)五.阅读理解,判断下列句子是否正确(10%)y name is Amy. I’m a thin girl. There are three members in my family. y parents and me. I have a good friend. She is iss Li, my Chinese teacher. She likes music. She is from China.( )1. Amy is strong.( )2. There are 4 members in Amy’s family.( )3. iss Li is Amy’s friend.( )4. iss Li likes painting.( )5. iss Li is from China.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.(5 分)如图为包含某逻辑电路的一个简单电路图,L 为小灯泡.光照射电阻R′时,其阻值将变得远小于R. 该逻辑电路是(填“与”或“非”)门电路.当电阻R′受到光照时小灯泡L将(填“发光”或“不发光”).【解析】由电路图可知,该逻辑电路为非门电路;当电阻R′受到光照时,R′的阻值减小,从而使R 两端的电压升高,即A 点的电势降低,经过非门逻辑电路后,使灯泡两端获得了高电压,因此灯泡将会发光.【答案】非发光14.(10 分)如图所示是小明设计的一种自动测定水箱内水位的装置,R 是一种滑动变阻器,它的金属滑片是杠杆的一端,从水位表指针所指的刻度就可知道水箱内水位的高低,从图中可知:水位表是由改装而成.当水面上升时,滑片,滑动变阻器连入电路电阻,电流,水量表示数.【解析】本题利用滑动变阻器滑片改变电阻,进一步改变电压,达到控制水位的目的.【答案】电流表向下移变小变大变大三、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)车床在工作时是不允许将手随便接近飞转的工件的,为了防止万一,设计了下面的光电自动控制安全电路,只要人手不小心靠近了工件,机器就自动停转,请简述其工作原理.图中的A 为车床上的电动机;B 为随电动机高速转动的工件;C 为光源,它发出的光照在光敏电阻D 上;E为电磁铁;F为衔铁;G为电源;H为弹簧.传【答案】 当手在C 、D 间靠近工件时,遮挡住射向光敏电阻的光,光敏电阻的阻值迅速变大,电路中的电流减小,使电磁铁磁性减弱从而放开衔接,造成电动机断路,使工件停转以保证安全.16.(13 分)如图所示为检测某传感器的电路图.传感器上标有“3 V,0.9 W”的字样(传感器可看做一个纯电阻),滑动变阻器 R 上标有“10 Ω,1 A ”的字样,电流表的量程为 0.6 A ,电压表的量程为 3 V .求:(1) 传感器的电阻和额定电流.(2) 为了确保电路各部分的安全,在 a 、b 之间所加的电源电压最大值是多少?【解析】 (1)R 传=U 2 /P 传=10 Ω,I 传=P 传/U 传=0.3 A(2)最大电流 I =I 传=0.3 A ,电源电压最大值U m=U 传+U,U 传为传感器的额定电压,U为R m=10 Ω时R两端的电压,即U=I 传·R m=0.3×10 V=3 V,未超过电压表量程,所以U m=U 传+U=3 V+3 V=6 V.【答案】(1)10 Ω0.3 A (2)6 V17.(14 分)在航天事业中要用角速度计测得航天器的自转角速度ω,结构如图所示,当系统绕轴OO′转动时元件A 在光滑杆上发生滑动,并输出电信号成为航天器的制导信号源,已知A 质量为m,弹簧的劲度系数为k,原长为l,电源电动势为E,内阻不计,滑动变阻器总长为l,电阻分布均匀,系统静止时滑动变阻器触头P 在中点,与固定接头Q 正对,当系统以角速度ω 转动时,求:(1)弹簧形变量x 与ω的关系式.(2)电压表示数U 与角速度ω的关系式.【解析】(1)由圆周运动规律知kx=mω2R=mω2(l+即kx-mω2x=所以x=k-mω2mω2l(2)由串联电路的规律U=l E=l x mω2l Ek-.【答案】(1)x=k-mω2mω2lmω2l E(2)U=l k-mω26.1 传感器及其工作原理课时作业基础达标1.下列说法正确的是( )A.传感器担负着信息采集的任务B.干簧管是一种磁传感器C.传感器不是电视遥控接收器的主要元件D.传感器是力、温度、光、声、化学成分转换为电信号的主要工具【解析】传感器是将力、温度、光、声、化学成分等非电学量转换为电学量的主要工具,在转换过程中,传感器担负着信息采集的任务,故A、D 正确;干簧管是一种利用软磁性材料制成的磁传感器,故B 正确;电视遥控接收器的主要元件是光电传感器,因此C 错误.【答案】ABD2.有一电学元件,温度升高时电阻却大幅度减小,则这种元件可能是( )A.金属导体B.绝缘体C.半导体D.超导体【解析】上述材料中只有半导体的电阻随温度升高而减少.故选C.【答案】C3.如图所示,截面为矩形的金属导体,放在磁场中,当导体中通有电流时,导体的上下表面的电势有什么关系( )A.U M>U NB.U M=U NC.U M<U ND.无法判断【解析】霍尔效应形成的原因是因为带电粒子在磁场中受到洛伦兹力作用,做定向移动形成的.根据左手定则,电子受到向下的洛伦兹力作用,向N 板运动,则M 板剩下正电荷,所以U M>U N.【答案】A4.如图所示,R、R为定值电阻,L 为小灯泡,R为光敏电阻,当照射光强度增大时( )A.电压表的示数增大B.R中电流减小C.小灯泡的功率增大D.电路的路端电压降低【解析】照射光照强度增大时,R变小,R、L 与R的并联电阻变小,因为I=E/(r+R+R 并),所以I 变大,因此电压表示数变大,A 正确;又U 外=E-Ir,I 变大,所以路端电压降低,D 正确;并联电路电压变小,流过R的电流减小,B 正确;总电流增大,所以流过L 和R的电流增大,小灯泡的功率增大,C 正确.【答案】ABCD5.关于干簧管,下列说法正确的是( )A.干簧管接入电路中相当于电阻的作用B.干簧管是根据热胀冷缩的原理制成的C.干簧管接入电路中相当于开关的作用D.干簧管是作为电控元件以实现自动控制的【解析】干簧管在电路中起到开关的作用,故C 选项正确,A 选项错误;干簧管是感知磁场信息的元件,故B、D 选项错误.【答案】C6.如图所示是电容式话筒的示意图,它是利用电容制作的传感器,话筒的振动膜前面有薄薄的金属层,膜后距膜几十微米处有一金属板,振动膜上的金属层和这个金属板构成电容器的两极,在两极间加一电压U,人对着话筒说话时,振动膜前后振动,使电容发生变化,声音信号被话筒转换为电信号,其中导致电容变化的原因可能是电容器两板间的( )A.距离变化B.正对面积变化C.介质变化D.电压变化【解析】C=εr S,在声音信号转换为电信号过程中介电常数ε4kπd r没变,正对面积S 未变.振动膜前后振动,使振动膜上的金属层与金属板间的距离发生变化,从而将声音信号转换为电信号,故A 选项正确.【答案】A7.有一些星级宾馆的洗手间装有自动干手机,洗手后将湿手靠近,机内的传感器就开通电热器加热,有热空气从机内喷出,将湿手烘干,手靠近干手机能使传感器工作,是因为( )A.改变湿度B.改变温度C.改变磁场D.改变电容【解析】根据自动干手机工作的特征,手靠近干手机电热器工作,手撤离后电热器停止工作,人是一种导体,可以与其他导体构成电容器.手靠近时相当于连接一个电容器,可以确定干手机内设有电容式传感器,由于手的靠近改变了电容大小,故D 正确;用湿度和温度来驱动电热器工作,理论上可行,但是假如干手机是由于温度、湿度的变化工作就成了室内烘干机.【答案】D8.如图所示是一火警报警器的一部分电路示意图,其中R为用半导体热敏材料制成的传感器,电流表为值班室的显示器,a、b 之间接报警器.当传感器R所在处出现火情时,显示器的电流I、报警器两端的电压U 的变化情况是( )A.I变大,U 变大B.I变小,U 变小C.I变小,U 变大D.I变大,U 变小【解析】抓住半导体热敏特性即电阻随温度升高而减小,再用电路动态变化的分析思路,按局部→整体→局部进行.当传感器R处出现火情时,温度升高,电阻减小,电路的总电阻减小,总电流I 增大,路端电压U=U=E-Ir 减小,I(r+R)增大,U 并=E-I(r+R)减小,通过R的电流I减小,通过R的电流I=I-I增大,D 对.【答案】D9.夜晚,楼梯上漆黑一片,但随着我们的脚步声响,楼梯灯亮了;我们登上一层楼,灯光照亮一层楼,而身后的灯则依次熄灭,这种楼梯灯好像能“听到”我们的到来,能“看见”我们的离去,之所以能如此,是因为电路中安装了光声控延时开关,探究这种开关有什么转换器件.【解析】打开光声控开关,内部构造如图.光声控延时开关中安装有光敏感元件,用于感知外界光线的强弱.还安装有声敏感元件用于感知外界声响.当白天外界光线较强时,光声控制延时开关总处于断开状态,灯不亮;当夜晚光线较弱且有声响时光声控延时开关处于导通状态,灯亮,延时一段时间后,开关断开,灯熄灭.【答案】见解析能力提升1.如图所示,R是光敏电阻,当开关S 闭合后在没有光照射时,。