热学考点扫描

热学考点扫描（精选3篇）

热学考点扫描 篇1

状语从句是指在主从复合句中用作状语的从句, 状语从句用来修饰主句中的动词、形容词、副词等。状语从句可分为时间、地点、原因、目的、条件、结果、方式、让步和比较状语从句。高考对状语从句的考查主要体现在从属连词的选择、状语从句与其他从句的辨析以及时态的正确使用上。弄清从属连词的意思, 根据语境选用合适的连词, 注意主从句时态的呼应是解题的关键。试题设问呈交叉和综合特点, 选项设计常常从定语从句和名词性从句的角度进行干扰。

一、时间状语从句

1. when, while和as引导的时间状语从句。

三者都可引导时间状语从句。when引导的时间状语从句的谓语动词可用延续性动词, 也可用非延续性动词。while引导的时间状语从句的谓语动词只能用延续性动词。as引导的时间状语从句强调主句和从句的动作都在发展变化, 强调动作同时发生, 不指先后, 常译为“随着……”。when还可用作并列连词, 表示“这时”之意。while还可用来表示对比、对照。例如:

It happened to be raining when we got to Beijing.

Don′t talk too much while you are eating.

As the children were walking along the street, they sang happily.

2. before和until引导的时间状语从句。

两者都可引导时间状语从句。before强调主句动词的动作与从句动词的动作之间的先后关系。before在引导时间状语从句时, 一般不用否定式谓语, 意为“……之前, 不到……就……, 还来不及……就, ……才……”。用在“It will be + 一段时间+before...”结构中, 意为“多久之后才……”。until表示动作的阶段性, 主句是肯定式而且动词为非延续性动词时, 不能用until。not ...until表示“直到……才”, 此时可用非延续性动词。例如:

He had left before I could have a word with him.

It will be five years before we meet again.

He worked until it was midnight.

He didn′t join the army until he was 20years old.

3. since引导的时间状语从句。

在since引导的从句里, 谓语动词是非持续性动词的过去式, 从该动作发生时算起;如果是持续性动词的过去式, 就从该动作结束时算起。例如:

He has worked hard since he entered this school. (entered是非持续性动词, 就从entered的动作发生时算起。)

We haven′t seen each other since I worked in this factory. (worked是持续性动词, 就从worked的动作结束时算起。)

It′s two years since he joined the army. (joined是非持续性动词)

It′s two years since he smoked. (smoke是持续性动词)

4. 表示“一……就……”的时间状语从句。

as soon as, immediately, instantly, directly, the moment, the minute, no sooner...han, hardly/scarcely... when等可引导时间状语从句, 表示“一……就……”。其中当no sooner和hardly/scarcely置于句首时, 主句的谓语动词用倒装句结构。在no sooner...than和hardly... when引导的时间状语从句中, 主句的谓语动词用过去完成时, 从句的谓语动词用一般过去时。例如:

The moment I got off the train, I saw my fa⁃ther.

I had hardly got home when the phone rang. = Hardly had I got home when the phone rang.

【典例1】If you miss this chance, it may be years ______ you get another one. (2015 年重庆卷)

A.as B.before

C.since D.after

解析:B。句型“It + will be + 时间段+ be⁃fore...”表示“要过多久才……”。句意:如果你错过这次机会, 可能要等好几年才会再有。

【 典例2】It was the middle of the night______my father woke me up and told me to watch the football game. (2014 年江西卷)

A. thatB. as

C. whichD. when

解析:D。when引导时间状语从句。句意:当我的爸爸把我叫醒, 告诉我看足球赛的时候, 已经是半夜了。

二、条件状语从句

常用if和unless引导条件状语从句, 其中unless引导条件状语从句时, 从句的谓语动词只能用肯定式, 相当于if...not。once (一旦) , as/so long as (只要) , in case (如果) 等也可引导条件状语从句。例如:

Small sailboats can easily turn over in the water if they are not managed carefully.

I′ll go there tomorrow unless it rains. = I′ll go there tomorrow if it doesnt rain.

Take your umbrella with you, in case it should rain.

I will lend my car to you as long as you return it on time.

【典例1】It is so cold that you can′t go outside ______ fully covered in thick clothes. (2015年江苏卷)

A.if B.unless

C.once D.when

解析:B。unless意为“除非”, 引导条件状语从句。句意:外面太冷, 你不要出去, 除非用厚衣服完全裹起来。

【典例2】You won′t find paper cutting difficult ______ you keep practicing it. (2015 年北京卷)

A.even though B.as long as

C.as if D.ever since

解析:B。even though“即使, 尽管”;as long as“只要”;as if“犹如, 好像”;ever since“自从”。结合句意可知选B。

【典例3】______ the damage is done, it will take many years for the farmland to recover. (2015年北京卷)

A. UntilB. Unless

C. OnceD. Although

解析:C。根据句意可知once在此用作连词, 意为“一旦”, 符合句意。

三、地点状语从句

where引导的地点状语从句, 常译为“在……地方”, 可放在句首或句末。例如:

Where there is a will, there is a way.

We should go where we are most needed.

The factory is built where two rivers come together.

He advised me to live where the air is fresher.

【典例1】______ he once felt like giving up, he now has the determination to push further and keep on going. (2015年安徽卷)

A. WhereB. As

C. In caseD. Now that

解析:A。考查状语从句。where在此引导一个地点状语从句, 意为“在……地方”。

【典例2】 Half an hour later, Lucy still couldn′t get a taxi ______ the bus had dropped her. (2014年重庆卷)

A.until B.when

C.although D.where

解析:D。考查状语从句。where引导一个地点状语从句。

四、让步状语从句

1. although与though引导的让步状语从句。

两者均可表示“虽然”, 一般可互换, 且可与still, yet连用, 不能与but连用。另外, though还可用作副词, 置于句末, 意为“然而”。例如:

Although/Though it was raining hard, they still went out.

She said she would come;she didn′t, though.

2.while与as引导的让步状语从句。

while位于句首时, 意为“虽然, 尽管”, 相当于although。as引导让步状语从句时, 通常用倒装语序, though引导让步状语从句也有这种用法, 但although不能这样用。例如:

Teacher as/though he is, he can′t know everything.

While the problem is very difficult, I don′t think it can′t be solved.

3. even if, even though, whether...or... 等引导的让步状语从句。例如:

I won′t mind even if he doesn′t come.

【典例1】______ the students came from different countries, they got along quite well in the summer camp. (2015年福建卷)

A.While B.Unless

C.Since D.Until

解析:A。while在此表示“尽管”之意, 引导让步状语从句。

【典例2】______ scientists have learned a lot about the universe, there is much we still don′t know. (2015年安徽卷)

A.Once B.Since

C.Though D.Unless

解析:C。though表示让步或转折。根据句意可知这里是转折含义, 故选C。

五、原因状语从句

1. 常用because, since, as, for, now that ( 既然) 等引导原因状语从句。这几个说明原因的连接词中because语气最强, 表示直接的因果关系, 回答why提出的问题。例如:

—Why didn′t she come to school?

—Because she was ill.

Now that he has come, I will tell him the truth.

2. for引导原因状语从句时, for不能置于句首。for表示的是解释性、补充性的理由, 常指推测的根据。列如:

The ground is wet, for it rained last night. 地面是湿的, 因为昨晚下过雨。

【典例】Mark needs to learn Chinese ______his company is opening a branch in Beijing.

A.unless B.until

C.although D.since

解析:D。考查状语从句。since在此意为“由于, 因为”, 符合句意。since在此引导原因状语从句。

六、目的及结果状语从句

1. so that, in order that引导目的状语从句;so...that, such...that...引导结果状语从句。例如:

He sat in the front of the classroom so that he might hear the professor more clearly.

She works hard at her lessons in order that she can get a good job in the future.

He was in such a hurry that he forgot to take his flight ticket.

2. in case, for fear that引导目的状语从句时, 从句的谓语动词要用 (should) +动词原形。例如:

You′d better take an umbrella in case it should rain.

3. so...that... 与such...that... 引导结果状语从句的区别。

①so+形容词/副词+that从句

such+ a/an+形容词+可数名词单数+that从句

②so+形容词+a/an+可数名词单数+that从句

such+形容词+复数名词/不可数名词+that从句

例如:

Jim is so clever a boy that we all like him. =Jim is such a clever boy that we all like him.

It is such fine weather that we all want to have a picnic outside.

【典例1】I′ll be out for some time. ______anything important happens, call me up immediately. (2014年四川卷)

A. In caseB. As if

C. Even thoughD. Now that

解析:A。in case意为“万一”, 在这里引导目的状语从句。

【典例2】Cathy had quit her job when her son was born______she could stay home and raise her family. (2014年浙江卷)

A.now that B.as if

C.only if D.so that

解析:D。so that引导目的状语从句。根据句意可知选D。

七、强化训练

(一) 单句语法填空

在下列句子的空白处填入适当的词语。

1.___________I admit your suggestionsounds reasonable, I won′t adopt it because it inot practical.

2.—Where is my e-dictionary?

—I′m sorry I am using it. I will return to you___________ I look up the new word.

3. The book appeals so much to readers___________ it caters well to the tastes of all ages.

4. In our city, housing prices are higher___________ there are key middle schools.

5. According to China′s environmental laws, a power plant has to pass an environmental impact assessment ___________ construction starts.

6.We cannot understand disease __________we understand the person who has the disease.

7. As a rule I catch the seven o′clock subway to work ___________ I can be sure of getting a seat.

8.Li Jianrou was lucky, ___________ all other three competitors stumbled in front of her in the women′s 500 meters short track final, making her China′ s first gold winner in the Sochi Winter Olympics.

9. Medicine should be kept ___________ it is not accessible to kids.

10. The fire was so big that it was several hours ___________ firefighters could get it under control.

11. Yaan, Sichuang is seeing improvements in life after the earthquake, ___________ life is still far from normal.

12.___________ the Internet is an anonymous (匿名的) electronic system, consumers want to feel as if the website owner knows about and cares about them as individuals.

13.—Every bird likes its own nest.

—Yes. A nest is to a bird ___________ a house is to a man.

14.___________I know, the computer can never take the place of the human brain.

15.____________ he comes back, I′ll go to pick him up at the airport.

16. —Mary looks so excited and happy.

—So will you ____________ you win the first prize in the next English speech competition.

17.____________ compared with the size of the whole earth, the biggest ocean doesn′t seem big at all.

18. I was so tired that I fell asleep___________ my head touched the pillow.

19. I thought her nice and honest____________ I met her.

20. ____________ asks her for advice, she is always ready to help.

21. Fewer visitors invited by him came___________ I expected.

22. It will not be long____________ we can have a trip to the moon.

23.____________ the days went on, the weather got worse.

24. If we work with a strong will, we can overcome any difficulty, ____________ great it is.

25. She is always listening to music___________ doing her homework.

26. They caught the thief. Then they bound his legs ___________ he couldnt escape.

27. He had to be called two or three times___________ he would come to his dinner.

28. ___________ bad weather stops me, I jog every day.

29. Take a hat with you during the trip___________ the sun is very hot.

30.____________ the job takes a significant amount of time, most students agree that the experience is worth it.

(二) 语篇型语法填空

阅读下面材料, 在空白处填入适当的内容 (1个单词) 或括号内单词的正确形式。

A

Eating a full English breakfast can help you lose weight, a new study suggests.

Research shows having sausage, egg1bacon instead of low-fat cereals ( 谷类食物) or fruit for the first meal of the day helps to fight2 (hungry) off and avoid the urge to overeat later in the day.

An experiment at the University of Missouri on a group of women3 (range) from 18years old to 55 years old showed a high protein breakfast4 (keep) them feeling full longer5a meal with less protein but the same amount of fat and fiber.

The team, 6was led by research scientist, Dr. Kevin Maki, found7 (eat) around 35 grams of protein for breakfast helped regulate (控制) appetite.

Dr. Heather Leidy, 8assistant professor, explained, “ In the USA, many people9 (choice) to skip breakfast or choose low protein foods because of a lack of high protein choices.”

Dr. Leidy said, “These results show proteinrich meals can help women feel full10lunchtime and potentially avoid overeating and improve diet quality.”

B

Once I had a loose tooth, I asked my father, a dentist, to examine it.“It needs1 (pull) , ”he told me. My dad took out some tissues (纱布) and I closed my eyes, 2 (expect) a sharp pain.I was still waiting for him to pull3I heard my father say, “I′m done.”I opened my eyes and saw my tooth in his tissue-covered hand. I4 ( feel) no pain at all. I thought my father was5magician.

The next day at school I bragged (吹嘘) to a friend about my father′s remarkable feat.6I explained that the process hadn′t hurt, my friend called me a liar. He said that when he had his tooth7 (pull) , it hurt a lot. I talked to my father about this and there was not a single mystery left after my father’s8 (explain) : my tooth had been ready to be extracted, 9my friend′s had not.

“I′m going to be a dentist, ”I declared. Years later, the dream of a child has not diminished but actually grown firmer. Now I realize that hard work is necessary to be a dentist. I must work hard to make my dream10 (come) true.

C

Thousands of female engineers have joined1Twitter campaign. They want to break down stereotypes (固定模式) . Their issue is about2female engineers should look like.

As of Aug. 6, more than 75, 0003 (woman) used the website Look Like An Engineer to post photos of themselves and promote gender4 ( diverse) in technology. The campaign started when Isis Anchalee, an engineer at tech startup One Login, attracted a lot of attention. It came after her photo5 (appear) in a recruitment ad for her company.

In the ad, Anchalee has long, wavy hair and wears glasses. She6 (see) smiling in a black T-shirt7 (bear) her company logo. Many people could not believe that an8 ( attract) woman could also be an engineer at a tech company.Some thought that the company had hired a model for its recruiting efforts.

“I didn′t want any of this attention. But9I can use this to put a spotlight on gender issues in tech, I consider that to be at least one win, ”she said. She suggested people10 ( use) the website to post photos of themselves.

参考答案与解析:

(一) 单句语法填空

1. While/Though/Although。本句是让步状语从句。句意:虽然我承认你的建议听起来有道理, 但我不会采纳它, 因为这个建议不实用。

2. the moment/as soon as。从属连词the mo ment/as soon as意为“一……就……”, 引导时间状语从句。

3. because。“___________ it caters well to the tastes of all ages.”是一个原因状语从句, 故用because引导。

4. where。从属连词where在此引导一个地点状语从句。

5. before。从属连词before在此引导一个时间状语从句。

6. unless。从属连词unless意为“除非”, 在此引导一个条件状语从句。

7. so that。从属连词so that意为“ 因此, 以便”。句意:我通常是赶七点的地铁去上班, 这样才能保证有座位坐。

8. as/because。从属连词as/because在此引导一个原因状语从句。

9. where。从属连词where引导地点状语从句, 常译为“在……地方”。

10. before。从属连词before在此意为“在……之前”。

11. though。though在此引导让步状语从句。

12. even though/if。even though/ if意为“即使”, 引导状语从句。

13. what。A is to B what C is to D. 意为“A对B而言正如C对D一样。”

14. As far as。as far as引导状语从句时, 意为“就……, 尽……”, as far as I know意为“就我所知”。

15.As soon as /The moment。as soon as /the moment引导时间状语从句。

16. if。if引导条件状语从句。句意:——Mary看起来很兴奋和高兴。——如果你在下次英语演讲比赛中得了一等奖的话, 你也会这样的。

17. When。本句是一个省略的时间状语从句。句意:当与整个地球大小相比较的时候, 最大的海洋似乎显得一点也不大。

18. As soon as /The moment。as soon as /the moment引导时间状语从句。句意:我是如此疲劳以至于我的头一挨枕头我就睡着了。

19. the first time/the moment/when。the first time/the moment/when引导时间状语从句。句意:我第一次见到他时, 我就觉得他好心和诚实。

20. No matter who。no matter who引导让步状语从句, 相当于whoever。句意:无论是谁向她请教, 她总是乐意帮忙。

21. than。根据fewer可以判断出这是一个比较状语从句, 故本句应填than。

22. before。“It will not be/was not long before...”, 意为“不久就……”。

23. As。as引导时间状语从句, 意为“随着”。as引导时间状语从句强调两个动作的发展变化。句意:随着时间的推移, 天气变得越来越差。

24. however。however引导让步状语从句。句意:如果我们意志坚强, 我们就可能克服任何困难, 不管困难有多大。

25. while。状语从句采用了省略形式, 后面可补充为“while she is doing her homework”。

26. so that。从后面的情态动词couldn′t可以判断出这是一个目的状语从句, 故用so that。so that意为“以便, 为了”, 引导目的状语从句。

27 before。before引导时间状语从句。根据句意可知应填before。

28. Unless。unless意为“除非”, 引导让步状语从句。句意:除非天气太差, 我每天都坚持慢跑。

29. in case。in case意为“万一, 以防”, 引导目的状语从句。

30. Although。although意为“虽然, 尽管”, 引导让步状语从句。

(二) 语篇型语法填空

A

【解题导读】本文为说明文。研究发现吃饱早餐, 吃好早餐有助于减肥。

1. Or。前后名词之间为选择关系, 故用并列连词or。

2. Hunger。应用名词作宾语。

3. ranging。用现在分词作定语, 修饰women。动词短语range from意为“从……到……变动”。

4. kept。根据主语的时态showed可知宾语从句的谓语动词也应用一般过去时态。

5. than。longer说明这里用了形容词的比较级形式, 故本空应填从属连词than。

6. which。非限制性定语从句缺少主语, 故填which。

7. eating。用动名词作句子的主语。

8. an。不定冠词在此表泛指。

9. choose。根据or后的choose可知本空应用choice的动词形式作谓语。

10. until。介词until在此意为“一直到……的时候”。

B

【解题导读】本文为记叙文。一个小孩在体验了父亲高超的拔牙技术后, 决定长大后成为像他父亲一样的牙医。

1. to be pulled。need后面应接不定式。且it与pull之间存在被动关系, 故用不定式的被动语态形式。

2. expecting。本空应用现在分词表示伴随状况。

3.when。并列连词when在此意为“这时”。

4.had felt。考查时态。feel的动作发生在opened my eyes之前, 故用过去完成时态。

5. a。不定冠词在此表示泛指。

6. When。从属连词when引导一个时间状语从句。

7. pulled。用过去分词作宾补。have sth.done意为“让/叫/使/请别人做某事”。

8. explanation。应用名词形式作宾语。

9.while。并列连词while在此表示“对照”。

10.come。动词make后面常接不带to的不定式作宾补, 故本空填come。

C

【解题导读】本文为记叙文。成千上万的女性工程师加入到了一个推特运动。她们想打破固有的女性工程师的形象, 塑造女性工程师全新的形象。

1. a。不定冠词在此表示泛指。

2. what。宾语从句缺少宾语, 故用what引导宾语从句。

3.women。此处应用名词的复数形式。

4.diversity。应用名词形式作宾语。

5. appeared。根据前面的时态可以判断出, 此处用一般过去时态。

6. is seen。she和see之间存在被动关系, 故用被动语态形式。根据前面的时态可知此处应用一般现在时态。

7. bearing。用现在分词作定语, 修饰T-shirt。

8. attractive。应用形容词作定语。

9.if。从属连词if引导一个条件状语从句。

10.use。考查虚拟语气。suggest后面的宾语从句要求用虚拟语气。

中考电学考点扫描 篇2

考点一、串并联电路的电流特点

电阻串联电路的总电流等于流过各电阻的电流。电阻并联电路的总电流等于流过各电阻的分电流之和。

例1根据如图1所示的用电流表测电流的实验, 回答下列问题。

(1) 按图1 (甲) 所示的电路连接好以后, 把电流表先后接在电路中的a、b、c处得到数据如下。比较测得的数据, 得出的结论是什么?

(2) 在图1 (乙) 中, 测得a处电流是1.2A;b处电流是0.7A。则在c处测得的电流值为多大?

解析:由图1中灯泡的连接方式可知, (甲) 图是串联电路, (乙) 图是并联电路。根据 (甲) 图中测得的电流可得结论:串联电路中各点电流相等;根据 (乙) 图中测得的电流, 知a点干路中电流1.2A是支路b点和c点通过的电流之和, 故c点的电流为:1.2A-0.7A=0.5A。

答案: (1) 串联电路中各处电流都相等; (2) 0.5A。

点评:串联电路电流特点的探究方法: (1) 分别测量电路中各点的电流大小, (2) 比较电路中各点电流的大小;并联电路电流特点的探究方法: (1) 分别测量干路中的电流和各支路中的电流大小, (2) 比较干路中电流和各支路电流的大小。

考点二、串并联电路的电压特点

电阻串联电路的总电压等于各电阻两端电压之和。电阻并联电路的总电压等于各电阻两端的电压。

例2如图2所示, 在探究“串联电路电压的关系”时, 电源电压恒定, 当开关S1闭合、S2断开时, 电压表的示数为3V;当S1断开、S2闭合时, 电压表的示数为4.5V, 则灯L1两端的电压为多大?灯L2两端电压为多大?

解析:由图2所示的电路图可以看出, 灯L1和L2串联接在电压恒定的电源上。当开关S1闭合、S2断开时, 电压表和L1并联, 测量的是L1两端的电压U1, U1=3V;当S1断开、S2闭合时, 电压表连接在L1和L2组成的串联电路两端, 测量的是串联电路的总电压U, U=4.5V。根据串联电路中的电压关系可得, 灯L2两端的电压U2=U-U1=4.5V-3V=1.5V。由分析可知, 在图2所示的电路中, 灯L1两端的电压为3V, 灯L2两端的电压为1.5V。

答案:3V;1.5V。

点评:本题考查考生应用所学知识综合分析问题的能力, 电压表接入电路测量时本身会对电路结构有影响。一般情况下, 将电路中的电流表视为导线, 没有电流通过的用电器视为导线, 将电压表视为断路 (因为电压表电阻很大, 电路中电流几乎为零) , 都是分析复杂电路结构常用的一种行之有效的方法, 学生应该能够熟练掌握。

考点三、电阻的串并联

理解串联电路的总电阻, 知道并联电路的总电阻, 会运用串、并联电路的知识分析解决简单的串、并联电路问题。

例3常用的电压表是由小量程的电流表G改装而成的。电流表G也是一个电阻, 同样遵从欧姆定律。图3 (甲) 是一个量程为0~3m A的电流表G, 当有电流通过时, 电流可以从刻度盘上读出, 这时G的两接线柱之间具有一定的电压。因此, 电流表G实际上也可以当成一个小量程的电压表。已知该电流表的电阻为R (G) =10Ω。

(1) 若将这个电流表当成电压表使用, 则刻度盘上最大刻度3m A处应该标多大的电压值?

(2) 如图3 (乙) 所示, 若将这电流表串联一个定值电阻R后, 使通过G的电流为3m A时, A、B之间的电压等于3V, 这样A、B之间 (虚线框内) 就相当于一个量程为0~3V的电压表 (图丙) , 求串联的定值电阻R的大小。

解析: (1) 根据欧姆定律, 得:

(2) AB之间的电阻:

因为R (G) 与R串联, 所以:

答案: (1) 0.03V, (2) 990Ω。

点评:本题考查的知识主要在高中传授, 但由于巧妙的两个设问, 降低了知识梯度, 立意高, 落点很低, 是一道非常好的试题。本题易错点主要是:考生不能用欧姆定律和串联知识解决此类问题。

考点四、欧姆定律

明确欧姆定律的实验思想和方法。控制电阻不变, 得到导体中的电流跟导体两端的电压成正比;控制导体两端的电压不变, 得到导体中的电流跟导体的电阻成反比。由此得到了电路中的电流与电压、电阻之间的关系, 因此, 如果已知其中的任何两个物理量, 都可以根据欧姆定律求出第三个物理量。

例4如图4所示, 在美国加利福尼亚州北部城市利弗莫尔消防站发动机室的天花板上, 悬挂着一个发着昏黄光亮的小灯泡。不过可不能因为它没有现在的节能灯明亮就小看它, 要知道自从1901年点亮以来, 这个灯泡就没有被熄灭过, 至今已持续工作了110个年头。一小灯泡的伏安特性曲线如图5所示, 在灯泡电压由3V增大到6V的过程中, 随温度的升高, 灯泡电阻改变了多少Ω?

点评:当导体的电阻率随温度变化显著时, R应是测量时的实际电阻, 这时欧姆定律仍可应用。欧姆定律是电学的基本定律和核心内容, 是中考的重中之重。熟练运用欧姆定律, 分析解决简单的电路问题是命题的热点。

考点五、电功和电功率

例5今年“十一”放假, 爸妈要外出旅游, 赵军征得他们的同意后, 设计了如下方案:让电视机处于待机状态, 拔掉其他所有电器的电源插头, 然后记下时间和家中电能表的读数;去爷爷家住3天后回来, 再记下此时的时间和电能表的读数。方案实施后, 请结合赵军记录的数据帮他算一算。

(1) 这三天里, 赵军家的电视机待机消耗的电能是多少?

(2) 赵军家电视机在待机状态下消耗的电功率是多少?

(3) 赵军所在市估计有近60万台电视机, 假设平均每台电视机每天处于待机状态15小时, 待机功率与赵军家电视机相同, 则每月 (按30天计算) 共浪费的电能约为多少?

(4) 如果这些电能全部用来烧水, 可以将多少15℃的水加热到40℃?如果赵军洗一次澡需要50kg40℃的水, 这些水可供他洗多少次澡?

解析: (1) 根据电能表读数的变化, 这段时间电视机消耗的电能为:

(2) 待机时间:t1= (3×24-2) h=70h,

(3) 共消耗电能:W=n·Pt2=6×105×0.01k W×15h×30=2.7×106k W·h;

(4) 设水所需要吸收的热量为Q, 则W=Q,

根据Q=cmΔt, 可知将15℃的水加热到40℃的质量为:

这些水可供小明洗澡的次数:

点评:电视机可以用遥控器关机而不用断开电源, 这种功能叫做待机功能。这一功能虽给人们带来了方便, 但电视机在待机状态下仍然要消耗电能却鲜为人知。由于电视机待机时仍需要消耗电能, 所以最好不要让电视机待机, 这样既可以节约电能, 又可以防止电视机发热而对电视机不利。通过上例的解析, 可使学生认识到在平时的学习和生活中就要了解有关能源的知识, 掌握节能方法, 如知道各种用电器在使用时的节电方法, 并且养成节能的好习惯, 树立可持续发展的意识, 以实际行动为建设节约型社会做出自己的贡献。

考点六、焦耳定律

焦耳通过大量实验精确地确定了电流产生热量跟电流强度、电阻和时间的关系:电流通过导体产生的热量, 跟电流的平方成正比, 跟导体的电阻成正比, 跟通电的时间成正比。即:Q=I2Rt。它适用于任何用电器热量的计算。

例6因存在极端情况下可能发生冒烟或起燃的安全隐患, 飞利浦 (中国) 投资有限公司自2011年5月31日起, 在中国地区召回3个型号共计175万余台飞利浦电吹风。如图6所示是电吹风的实物连接图, 其中发热电阻丝的阻值为50Ω, 求: (1) 电吹风吹冷风时, 测得插头处的电流为0.2A, 此时电吹风消耗的电功率? (2) 电吹风吹热风时, 正常工作2min, 电流通过电吹风做的总功是多少?

解析: (1) 电吹风吹冷风时, 消耗功率:

(2) 发热电阻丝功率:

考点七、电能表参数

观察电能表铭牌上的两个主要数据: (1) 电压与电流的参数 (如“220V10A”即表示该电能表只能在电压为220V的电路上使用, 允许通过的最大电流为10A) ; (2) 转盘消耗单位电能的转数 (如“3000r/k W·h”表示该电能表在电路上消耗了1k W·h的电能时, 转盘转3000圈) 。

例7如图7所示, 许多家庭都装上了电能表, 表上标有1950r/k W·h。当你打开电灯或其他用电器时, 电能表里的圆盘便转起来, 数字窗里的读数也慢慢增加。月底的时候查看电度表里的数字, 就能知道你家这个月用了多少电。使用电能表与使用手表一样, 总希望它能计量准确。精确地校对电能表准不准, 需由专业计量部门进行。你能不能设计一个实验大致估量一下家中的电能表走得准不准?

虚拟语气高考考点扫描 篇3

一、高考常考点

(一) if引导的虚拟条件句

【典例1】Why didn’t you tell me aboutyour trouble last week?If you___________ (tell) me, I could have helped. (2016年北京卷)

解析:had told。根据主句谓语“could havehelped”可以判断此句表示与过去的事实相反, 所以从句谓语用过去完成时。

【典例2】If I__________ (see) it with myown eyes, I wouldn’t have believed it. (2015年北京卷)

解析:hadn’t seen。根据主句谓语“wouldn’thave believed”可以判断此句表示与过去的事实相反, 所以从句谓语用过去完成时。

【典例3】We__________ (be) back in thehotel now if you didn’t lose the map. (2014年北京卷)

解析:would be。根据主句中的时间状语now可知, 主句表示与现在的事实相反, 所以本空填would be。

【典例4】Grace doesn’t want to move toNew York because she thinks if she___________ (live) there, she wouldn’t be able to see herparents very often. (2012年安徽卷)

解析:were to live/should live/lived。根据句意可知, 表示与将来的事实可能相反, 所以本空填were to live/should live/lived。

【注意】此外这种表示假设条件的虚拟语气还可以倒装, 首先将从句中的连词if去掉, 把句中的were, should, had提到主语之前。

【典例5】 (单句改错) Have the governments and scientists not worked together, AIDS-related deaths would not have fallen since their highest in 2005. (2016年浙江卷)

解析:把have改为had。根据题干中的“would not have fallen”可知主句是对过去的虚拟, 所以从句用“if the governments and scien-tists had not worked together”与主句保持一致。If引导的虚拟条件句中含有had时, 可将if省去, 将had提前到主语之前构成倒装结构。

【典例6】__________there no modern telecommunications, we would have to wait for weeks to get news from around the world. (2014年福建卷)

解析:Were。根据主句谓语用“would+动词原形”以及句意可知, 表示对现在情况的虚拟, 条件句中用一般过去时, 将连词if去掉, 则把were提到主语之前。

(二) 含蓄条件句

有时假设的情况并不是以条件从句形式表现出来, 而是通过暗含的含蓄条件with, without, but, but for, but that, or, otherwise引起的短语或句子来代替if引导的虚拟条件句。

【典例1】Without his wartime experiences, Hemingway____________ (write) his famous novel A Farewell to Arms. (2015年重庆卷)

解析:wouldn’t have written。根据句中的“without his wartime experiences”可知描述的情况是对过去情况的否定猜测, 故主句用wouldn’t have written。

【典例2】It is lucky we booked a room, orwe__________ (have) nowhere to stay now. (2015年安徽卷)

解析:would have。or引导含蓄虚拟条件句, 相当于“if we hadn’t booked a room, wewould have nowhere to stay now.”根据句中的now可知, 是对现在情况的虚拟, 故本空填would have。

【典例3】We lost our way in that smallvillage, otherwise we__________ (visit) moreplaces of interest yesterday. (2012年福建卷)

解析:would have visited。根据句中的时间状语yesterday可知, 本题是对过去情况的虚拟, 前句表示“我们在那个小山村迷路了”这一过去的客观事实, otherwise后接的句子是对过去的虚拟, 故本空填would have visited。

【典例4】We__________ (put) John’s name on the race list yesterday but for his recent injury.

解析:would have put。but for相当于with-out, 可与if引导的虚拟条件句替换;由句意可知, 与过去事实相反, 故本空填would have put。

【典例5】People are recycling many thingswhich they__________ (throw) away in the past. (2014年安徽卷)

解析:would have thrown。此句是由which引导的定语从句, 是一个隐含的虚拟语气, innthe past相当于“If they had been in the past”, 所以此定语从句应用虚拟语气, 表示与过去的事实相反, 故本空填would have thrown。

【注意】without/but for…=if it were not forsth/if it had not been for sth.=were it not forsth/had it not been for sth.要不是, 若非。

【典例6】 (完成句子) If it___________ (要不是) his invitation the other day, I should notbe here now. (2016年江苏卷)

解析:had not been for。根据从句中的时间状语“the other day”可知, 从句表示与过去的事实相反, 主句表示与现在的事实相反, 从句谓语应用过去完成时。

(三) wish (if only, as if/though) 后接从句中的虚拟语气

1.wish+宾语从句。

【典例1】Ellen is a fantastic dancer.I wishI___________ (dance) as well as her. (2015年陕西卷)

解析:danced。wish后接的宾语从句应用虚拟语气, 表示与现在事实相反, 从句用一般过去时。

【典例2】 (单句改错) I wish I were at mysister’s wedding last Tuesday, but I was on abusiness trip in New York then. (2015年天津卷)

解析:把were改为had been。根据句意与句中的时间状语last Tuesday可知, 表示与过去事实相反的愿望, 从句用过去完成时。

2.if only+陈述句。常用虚拟语气, 表示愿望, 意为“要是……就好了”。“if only+句子”相当于“How I wish+that从句”。

【典例】 (单句改错) If only he lay quietly asthe doctor instructed, he would not suffer somuch now.

解析:把lay改为had lain。根据语境可知, 此句表示过去不能实现的愿望, 因此从句用过去完成时。

3.在as if/as though引导的方式状语从句或表语从句中, 常用虚拟语气。

【典例1】 (单句改错) It was John who brokethe window.Why are you talking to me as if Idid it? (2014年重庆卷)

解析:把did改为had done。根据前一句中的was可知, 打破玻璃是过去发生的事情, 表示与过去事实相反, 所以as if引导的方式状语从句应用过去完成时。

【典例2】Don’t handle the vase as ifit__________ (be) made of steel. (2012年北京卷)

解析:were。根据语境可知, as if引导的状语从句表示与现在事实相反的虚拟语气, 从句谓语动词用一般过去时, 如果谓语动词是be动词, 应使用were。

【注意】在as if/as though从句中, 有时用陈述语气, 这是因为从句中的情况往往是可能发生的或者可能被设想为真实的。例如:Look at the dark clouds.It looks as if it’s going to rain!

(四) would rather后接从句中的虚拟语气

【典例】 (单句改错) We would rather our daughter had stayed at home with us, but it is her choice, and she is not a child any longer. (2014年陕西卷)

解析:去掉had。would rather后接的从句用虚拟语气, “but it is her choice”表明是对现在的虚拟, 故用动词的一般过去时。

(五) should型虚拟语气

1.宾语从句中的虚拟语气

一个坚持 (insist) , 二个命令 (order, com-mand) , 三个要求 (demand, request, require) , 四个建议 (suggest, advise, propose, recommend) 与desire (希望, 渴望) 等动词后接的宾语从句中, 从句谓语用“ (should) do”形式。

【典例1】 (单句改错) Some classmates sug-gest we can go to places of interest nearby. (2016年全国卷II)

解析:删除can或把can改为should。动词suggest表示“建议”, 后接的宾语从句要用虚拟语气, 从句中的谓语用“ (should) +动词原形”, 所以本句可以删除can或把can改为should。

【典例2】Eye doctors recommend that achild’s first eye exam___________ (be) at theage of six months old. (2013年浙江卷)

解析: (should) be。recommend表示“建议”时, 后接宾语从句中的谓语动词用“should+动词原形”的形式, should可省略。

【注意】suggest作“建议”讲时, 从句用虚拟语气, 谓语动词用“should+动词原形”, should可以省略;suggest作“表明, 暗示”讲时, 从句不用虚拟语气;insist作“坚持要求”讲时, 从句用虚拟语气, 谓语动词用“should do”形式, should可以省略;insist作“坚持认为/说”讲时, 从句不用虚拟语气。

2.主语从句中的虚拟语气

在主语从句“It is necessary/important/es-sential/strange/unusual/natural/surprising/sug-gested/required/ordered/a pity/a shame/nowonder/+that从句”的结构中, that从句的谓语有时用“ (should) do”这样的虚拟语气形式。

【典例】 (单句改错) In this country it is re-quired that anyone who have recently come herehave to pass this kind of test.

解析:把第一个have改为has。由that引导的主语从句要用虚拟语气, 而这个主语从句中又嵌套了一个定语从句, 定语从句不能用虚拟语气;此外定语从句谓语动词的单复数应与其前的先行词anyone保持一致, 所以定语从句的谓语动词应用第三人称单数。

3.表语从句和同位语从句中的虚拟语气

在order, command;demand, request, re-quirement;advice, suggestion, recommendation, proposal, plan, idea等名词后的表语从句、同位语从句中, 谓语用“ (should) do”形式。

【典例】 (单句改错) After my effort, I at lastpersuaded him into taking my advice that he wasoperated on at once.

解析:把was改为 (should) be。advice意为“建议”, 后接的同位语从句中用虚拟语气, 谓语动词用“should do”形式, should可以省略。

(六) “It is (about/high) time+that从句”结构

【典例】 (单句改错) Jack is a great talker.It’s high time that he do something instead ofjust talking.

解析:把do改为did或在do前加should。在句型“It’s high/about time that从句”中, 从句中的谓语动词用过去式或should do, 但should不可省略。

二、高考易错易混点

(一) 错综时间条件句

有时条件从句与主句的动作发生的时间有先后之差, 这时应按各自的动作时间搭配来调整相应的结构形式。

【典例1】If he had spent more time prac-ticing speaking English before, he would havebeen able to speak it much better now. (2013年天津卷)

解析:把have been改为be。此题是由if引导的虚拟条件句。根据从句的时间状语before可知, 从句表示与过去的事实相反, 所以从句用过去完成时态;根据主句的时间状语now可知, 表示与现在的事实相反, 因此把have been改为be。

【典例2】If we booked a table earlier, wecouldn’t be standing here in a queue. (2013年北京卷)

解析:在booked前加had。根据语境可知, 这是一个错综虚拟条件句。从句表示与过去的事实相反, 所以从句用过去完成时。

(二) 虚实错综句

所谓“虚实错综句”是指虚拟现象与客观事实错综交织在一起的句子, 这就要我们细心判断哪一处应使用虚拟语气, 哪一处应使用陈述语气。

【典例1】 (单句改错) I would go to mycousin’s birthday party last night, but I was notavailable. (2013年安徽卷)

解析:把go改为have gone。这是由but引导的虚实条件句, 根据句中的时间状语lastnight可知, 前一句表示与过去的事实相反, 所以用“would+have done”形式;第二个句子陈述过去的事实, 不用虚拟语气。

【典例2】 (单句改错) We could face the dif-ficulty together, but why didn’t you tell me? (2012年北京卷)

解析:把face改为have faced。句中的“but why didn’t you tell me”表示过去的真实情况;第一个句子表示与过去的事实相反, 是对过去情况的虚拟, 故把face改为have faced。

三、巩固性练习

(一) 单句填空, 用所给动词的适当形式填空。

1.If it________ (be) not for the climate, Iwould stay here much longer.

2.If he_________ (insist) that he_________ (go) to work there, everything would be OK now.

3.—It________ (be) cool if I won this con-test.I don’t think I’m good enough, though.

—Give it a shot.You never know.

4.We________ (not finish) the project ontime without your timely help.

5.I would rather_________ (go) to work af-ter my graduation, but my father would ratherI_________ (go) abroad for further education.

6.The upset mother thought to herself, “Ifonly I________ (know) what’s going on in mylittle boy’s head right now.”

7.It is required by law that enough evi-dence________ (provide) to prove one is inno-cent of a crime.

8.—Jeff, what’s up?You are not yourselftoday.

—Oh, Mom.I really wish I________ (get) the chance but I failed.

9.Don’t be angry with us.We__________ (eat) out with you together, but we were busywith our final reports when you called in.

10.But for the fact that China_________ (be) also affected by the global economic crisis, we_________ (have) fewer unemployed workersnow.

11.Jane’s pale face suggested that she__________ (be) ill, and her parents suggestedthat she_________ (have) a medical examination.

12.The teacher’s suggestion that we__________ (try) once more is a great encourage-ment to us.

13.The constant rise of meat price requiresthat effective measures__________ (take) by thegovernment.

14.Had it not been for my teacher’s help, I__________ (win) the first place in the EnglishOral competition.

15.If you had listened to me, we_________ (be) at the party now.

16.They could have escaped from the bigfire, but unfortunately, someone__________ (lock) the door.

17._________he_________ (be) here yes-terday, he would attend the lecture with us today.

18.If we had taken such effective measuresmuch earlier, the river__________ (not pollute) so seriously now.

19.—Max looks nervous.

—So_________you if you had so fierce acompetition.

20.It was lucky that little Jack was not athome when the fire broke out;otherwise, he________ (lose) his life.

(二) 单句改错

1.I think it is about time that we hold ameeting to discuss this problem.

2.When you phoned me, I was having ameeting;how I wish I answered your call.

3.The girl insisted that she wasn’t wrongand that she was sent back to the classroom.

4.—Why didn’t you come to the party?

—Well, I should, but I had an unexpectedguest at that moment.

5.It is ordered that no smoking is allowedin public places.

6.Had you listened to your mother, youwould have been all right now.

7.But for your timely help, I would be inthe traffic jam for a long time.

8.They met for the first time, but they talk-ed happily as if they were good friends for along time.

9.Would you need any help, you could al-ways phone me at the office.

10.Without the greenhouse effect, the Earthwere about thirty-three degrees Celsius coolerthan it is.

(三) 语篇填空

Over years I have been wishing I1.__________ (be) a bird flying freely in the clear and clean sky.However, the earth is becoming warmer and warmer and it is human activity that has caused this global warming.People suffer more from the natural disasters, pollution, global warming and so on.If only we2.__________ (can breathe) clean and fresh air every day!

What do you suggest that we 3.__________ (do) to save our earth?When everything is out of order, it looks as if the world 4.__________ (end) .It is high time that some effective measures 5._________ (take) to stop the damage to the earth, otherwise, the earth 6._________ (destroy) by human beings.

It is obvious that it is the efforts people make that make it possible for the environment to become clean.The main focus of effort must be to reduce global greenhouse gas emissions now.In our daily life, we should try to save electricity, water and gas;we should also start recycling.What’s more, if everyone7._________ (take) public transportation in the future, there 8._________ (be) less pollution in the air and the environmental problems9.__________ (improve) .I do desire that one day the earth 10._________ (become) as beautiful as before.

(一) 单句填空

1.were。根据句意以及主句的谓语woulddstay可知, 表示与现在的事实相反, 从句谓语用动词的过去时, be动词常用were。

2.had insisted; (should) go。此句是错综虚拟语气, 从句表示与过去的事实相反, 所以从句谓语用过去完成时;insist表示“坚持要求”, 后接宾语从句中的谓语应用虚拟语气, 形式是“should+动词原形”, should可省略。

3.would be。根据句意与从句中的谓语won可知, 本句表示与将来的事实可能相反, 所以主句谓语用would be。

4.wouldn’t/couldn’t have finished。此句是含蓄条件句, 表示与过去事实相反, 所以本空填wouldn’t/couldn’t have finished。

5.go;went。“would rather+动词原形”表示宁愿现在或将来做某事, 所以第一空用动词原形;“would rather+从句”表示与将来的愿望可能相反, 所以从句谓语用一般过去时。

6.knew。if only意为“要是……就好了”, 谓语动词应用虚拟语气, 根据句中的right now可知, 此句表示对现在的事实相反, 所以谓语应用一般过去时。

7. (should) be provided。此句是由that引导的主语从句, require表示“要求”, 与其相关的名词性从句应用虚拟语气, 形式是“ (should) +do”;provide与evidence构成动宾关系, 所以此空还应用被动语态。

8.had got。wish后面接的宾语从句应用虚拟语气, 从“but I failed”可知表示与过去事实相反, 所以此句应用过去完成时。

9.could have eaten。此处表示与过去的情况相反, 主句谓语用could have done, 表示“过去本来能够/本来会……的, 但实际情况不是这样”。

10.is;would have。此句是由but for引导的含蓄条件句, that后接同位语从句, 指现在的情况, 是事实, 所以第一空用一般现在时, 而后句表示与现在的情况相反的虚拟语气, 形式是“would+动词原形”。

11.was; (should) have。suggest作“表明, 暗示”讲时, 从句用陈述语气, 所以第一空填was;suggest作“建议”讲时, 从句用虚拟语气, 谓语动词用“should+动词原形”, should可以省略, 所以第二空填 (should) have。

12. (should) try。此句是由that引导的同位语从句, suggestion表示“建议”, 与其相关的名词性从句应用虚拟语气, 形式是“ (should) +do”。

13. (should) be taken。此句是由that引导的宾语从句, require表示“要求”, 与其相关的名词性从句应用虚拟语气, 形式是“ (should) +do”;take与measures之间构成动宾关系, 所以此空还应用被动语态。

14.wouldn’t have won。根据句意可知, 表示与过去的事实相反, 应用“wouldn’t+havedone”形式。

15.would be。此句是错综虚拟语气, 从句表示与过去事实相反, 而主句表示与现在的情况相反, 所以本空填would be。

16.had locked。根据句中的“could haveeescaped”可知, 此句表示与过去事实相反的虚拟语气, 因此此空表示过去, lock先于“coulddhave escaped”这一动作, 即表示“过去的过去”, 所以此空用过去完成时。

17.If;had been或Had;been。此句是错综条件句, 从句表示与过去的事实相反, 所以从句用过去完成时, 所以第一空填If, 第二空填had been;如果把连词if去掉, 应把助动词had放在句首, 即第一空填Had, 第二空填been。

18.would not be polluted。此句是错综条件句, 主句表示与现在的事实相反, 所以用“would not+动词原形”;pollute与the river之间构成动宾关系, 因此此句还应用被动语态。

19.would。本句中主句和if条件从句都表示与现在事实相反的假设, 可改为“Youwould also look nervous if you had so fierce acompetition.”然后采用“so+情态动词would+主语”替换主句形式。

20.would have lost。此句是由otherwise引导的含蓄条件句, 表示与过去事实相反, 所以本空填would have lost。

(二) 单句改错

1.把hold改为held或在hold前加should。在“It is (about/high) time+that从句”结构中, 从句谓语用一般过去时或“should+动词原形”, 但should不可省略。

2.在answered前加had。wish后接的宾语从句应用虚拟语气, 根据句意可知, 表示与过去的事实相反, 从句用过去完成时, 所以在an-swered前加had。

3.把was改为be。insist作“坚持要求”讲时, 从句用虚拟语气, 谓语动词用“should do”形式, should可以省略;insist作“坚持认为/说”讲时, 从句不用虚拟语气。所以应把was改为be。

4.在should后加have。根据句意可知, 表示过去本应该做某事而实际上没有做到, 所以在should后加have, 在省略句中用助动词have代替完成式。

5.把第二个is改为be。此句是由that引导的主语从句, order意为“命令”, 与其相关的名词性从句应用虚拟语气, 形式是“ (should) +do”, 所以此句应把is改为be。

6.把have been改为be。此句是错综条件句, 从句表示与过去事实相反, 而主句表示与现在的情况相反, 所以应把have been改为be。

7.把be改为have been。此句是含蓄条件句, 表示与过去事实相反, 所以应把be改为have been。

8.把were改为had been。此句是由as if引导的方式状语从句, 根据句意可知, 表示与过去的事实相反, 所以从句谓语用过去完成时, 所以应把were改为had been。

9.把Would改为Should。根据句意可知, 表示与将来的事实可能相反, 应把Would改为Should。

10.把were改为would be。此句是含蓄条件句, 表示与现在的事实相反, 所以应把were改为would be。

(三) 语法填空

【语篇解读】本文讲述了由于人类活动导致全球变暖, 对此我们应采取一些应对措施。

1.were。wish后接宾语从句, 根据句意可知, 表示与现在的事实相反, 从句应用一般过去时, 所以此空填were。

2.could breathe。if only意为“要是……就好了”, 根据句意可知, 表示与现在的事实相反, 从句应用一般过去时, 故填could breathe。

3. (should) do。suggest表示“建议”, 后接宾语从句时应用虚拟语气, 从句谓语用“ (should) +动词原形”, should可省略。

4.ended。在as if引导的方式状语从句或表语从句中, 常用虚拟语气, 根据句意可知, 表示与现在的事实相反, 从句应用一般过去时, 所以此空填ended。

5.should be taken或was taken。take与mea-sures之间构成动宾关系, 所以此空应用被动语态;在“It is (about/high) time+that从句”结构中, 从句谓语用一般过去时或“should+动词原形”, 但should不可省略。

6.would be destroyed。destroy与the earth之间构成动宾关系, 因此此句应用被动语态;此句是由otherwise引导的含蓄条件句, 根据句意可知, 表示与现在的事实相反, 所以此处填would be destroyed。

7.takes。此句是由if引导的真实条件句, 表示将来的概念, 从句应用一般现在时代替一般将来时, 所以此空填takes。

8.will be。此句是由if引导的真实条件句, 表示将来的概念, 主句应用一般将来时, 所以此空填will be。

9.will improve。此句是由if引导的真实条件句, 主句又嵌套了一个由and引导的并列句;表示将来的概念, 主句应用一般将来时, 所以此空填will improve。