中考物理专项练习练习电表示数变化.doc

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2021中考物理专项练习练习-电表示数变化（粤沪版）
1、如图4所示，电路中的电源电压保持不变。闭合开关后，将滑动变阻器的滑片P由图中位置向A点移动时，电表V1、V2、A的示数变化正确的选项是〔〕
A、V1减小，V2减小，A增大
B、V1增大，V2减小，A增大
C、V1增大，V2减小，A减小
D、V1减小，V2增大，A减小
解析：
2、如图2所示电路，电源两端的电压一定，开关S1闭合，S2断开。如果使电压表和电流表的示数均增大，那么以下操作一定可行的是
A、滑动变阻器的滑片P向右移
B、滑动变阻器的滑片P向左移
C、滑动变阻器的滑片P不动，闭合开关S2
D、滑动变阻器的滑片P不动，断开开关S1
解析：
3、如图3所示，电源电压不变，当开关闭合，滑动变阻器的滑片P由图示位置向A点滑动的过程中，以下判断正确的选项是〔〕
电压表示数增大，电流表示数增大
B、电压表示数不变，电流表示数增大
C、电压表示数减小，电流表示数减
D、电压表示数不变，电流表示数减小
解析：

4、如图12所示电路中，电源电压不变，闭合开关S，在滑动变阻器的滑片P向右移的过程中，A1、A2、V的示数变化情况是〔〕
A、A1变小、A2不变、V不变
B、A1变小、A2变小、V不变
C、A1变小、A2不小、V变大
D、A1变大、A2不变、V变小
解析：
5、如图所示的电路，电源电压保持不变，闭合开关后，灯L能够发光，当滑片P向左滑动过程中，以下判断正确的选项是
A、电压表示数变小，电流表示数变大
B、电压表示数变大，电流表示数变小
C、电压表示数变大，电流表示数变大
D、电压表示数变小，电流表示数变小
解析：
6、如图2所示的电路，电源电压和灯丝电阻保持不变，开关S闭合后，在滑动变阻器滑片向左滑动过程中，电压表V的示数＿＿＿＿，电流表A1的示数＿＿＿＿，电流表A2的示数＿＿＿＿.（填“变大”、“变小”或“不变”）
解析：
7、如图8所示，电源电压恒定不变，当S闭合，滑动变阻器的滑片向右移动过程中，以下说法正确的选项是（）
A、灯泡变亮，电压表读数不变 B、灯泡变暗，电压表读数变小
C、灯泡变亮，电压表读数变大D、灯泡变亮，电压表读数变小
解析：
8、如下图所示的电路，当开关由断开变为合上时，各表的示数变化为 【】
A、两表的示数都变小B、两表的示数都变大
C、电流表的示数变大，电压表的示数变小
D、电流表的示数变大，电压表的示数不变
解析：
9、如下图所示，当滑动变阻器的滑片P向左滑动时，电流表和，电压表的示数变化是 【】
A、电流表、示数变小，电压表示数变大
B、电流表、示数变小，电压表示数不变
C、电流表、示数变大，电压表示数变大
D、电流表、示数变大，电压表示数不变
归纳与反思：

1、用字母表示数（一）
一、填空：
1、学校有图书4000本，又买来ａ本，现在一共有（　　　）本。
2、学校有学生ａ人，其中男生ｂ人，女生有（　　　　）人。
3、李师傅每小时生产ｘ个零件，10小时生产（　　　　）个。
4、食堂买来大米400千克，每天吃ａ千克，吃了几天后还剩ｂ千克，已吃了（　　　）天。
5、姐姐今年ａ岁，比妹妹年龄的2倍少2岁，妹妹今年（　　　　）岁。
6、甲数是ｘ，比乙数少ｙ，甲乙两数之和是（　　　　），两数之差是（　　　）
二、根据运算定律填空。
1、ａ＋18＝□＋□ａ×15＝□×□
2、ｍ×2.5×0.4＝□×（□×□）
3、（ａ＋ｂ）×C＝□×□＋□×□
4、ｍ－ａ－ｂ＝□－（□＋□）
三、省略乘号写出下面各式。
ａ×12＝　　　　　ｂ×ｂ＝　　　　　　ａ×ｂ＝　　　　　ｘ×ｙ×7＝
5×ｘ＝　　　　2×ｃ×ｃ＝　　　　　7ｘ×5＝　　　　　2×ａ×ｂ＝
四、判断。（对的打“√”，错的打“×”。）
1、5＋ｘ＝5ｘ（　　　）　　　　　　　　　2、ｘ＋ｘ＝ｘ2（　　　）
3、ａ×3＝3ａ（　　　　）　　　　　　　　4、ｙ2＝ｙ×2（　　　　）
5、2ａ＋3ｂ＝5ａｂ（　　　）　　　　　　6、2ａ＋3ａ＝5ａ（　　　）
7、5×ａ×ｂ＝5ａｂ（　　　）　　　　　8、ａ×7＋ａ＝8ａ（　　　）
用字母表示数（二）
一、口算。
32＝（　　　）　　　　　0.2×0.4＝（　　　　）　　　　　6÷0.6＝（　　　　）
0.12＝（　　　　）　　　0.81÷0.9＝（　　　　）　　　　　1.52＝（　　　）
二、说一说下面每个式子所表示的意义。
（1）、一天中午的气温是32℃，下午比中午的气温降低了ｘ℃。
32－ｘ表示：＿＿＿＿＿＿＿＿＿＿＿＿＿
（2）、五（2）班有40人订阅《少年文艺》杂志，每本单价ｂ元。
40ｂ表示：＿＿＿＿＿＿＿＿＿＿
（3）、一个足球单价ａ元，一个篮球ｂ元。
6ａ＋4ｂ表示：＿＿＿＿＿＿＿＿＿＿
（4）、张师傅每小时加工ｘ个零件，朱师傅每小时加工15个零件
ｘ－15表示：＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿
5ｘ表示：＿＿＿＿＿＿＿＿＿＿＿＿＿
（ｘ－15）×3表示：＿＿＿＿＿＿＿＿＿＿
三、先写出图形的计算面积的公式，再把数字代入公式进行计算。
（1）、一个平行四边形底是12分米，高是8分米，求面积？

（2）、一个三角形底是4.8厘米，高是底的2倍，求面积？

（3）、一个梯形上底是15厘米，下底是9厘米，高8厘米，求m2＋n2面积？

用字母表示数（三）
一、填空。
（1）、小花今年12岁，比小兰大ａ岁，小兰今年（　　　）岁。
（2）、一件上衣54元，一件裤子48元，买b套这样的衣服，要用（　　　　　）元。
（3）、一本故事书有ａ页，小明每天看ｘ页，看了ｙ天，看了（　　　）页，还剩（　　　）页没看。
（4）、王阿姨买了ｍ千克香蕉和ｎ千克苹果，香蕉每千克4.8元，苹果每千克5.4元，一共花了（　　　　　　）元。
二、求下列各式的值。
（1）、已知ａ＝1.8　ｂ＝2.5求4ａ＋2ｂ的值

（2）、已知ｘ＝0.5，ｙ＝1.3　求3ｙ－4ｘ的值

（3）、已知ｍ＝0.6。ｎ＝0.4，求ｍ2＋ｎ2的值

三、应用题。
1、有两筐同样的梨，第一筐重ａ千克，第二筐重ｂ千克，第一筐比第二筐少卖ｍ元，（1）、用式子表示出梨的价钱。（2）、当ａ＝24，ｂ＝27，ｍ＝9时，每千克梨价钱是多少元？

2、甲书架上有ｘ本书，乙书架上的书比甲书架上的1.5倍还多5本，（1）、用式子表示乙书架上有多少本书。（2）当ｘ＝45，乙书架上有书多少本？

初三阅读与表达专项练习及答案
1.阅读与表达（共8分，每小题2分）
阅读短文，根据其内容回答问题。
What is a hurricane (飓风)?
You may already know that hurricanes are storms, they can cause devastating (毁灭性的) waves, wind, and rain. They happen during “Hurricane Season,” which is from June 1st until November 30th in the Atlantic Ocean and from May 15th until November 30th in the Pacific Ocean.
Categories (类别) of Hurricanes
There are five categories of hurricanes, which are based on wind speeds. The categories help people know how much damage (危害) a hurricane may cause because the greater the wind speed, the more dangerous the storm. For example, a Category 5 hurricane has winds over 155 miles per hour, they are strong enough to destroy the buildings along the shorelines completely.
Hurricane Dangers
When a hurricane happens together with heavy rainfall, there can be a devastating flood (洪水). The center of a hurricane is called the eye. While most of a hurricane has dangerously strong winds, the eye is actually a calm (平静的) area in the storm. When the eye of a hurricane passes over land, people might think that it’s over, but before long the wind and rain increase again as the second part of the hurricane moves through.
Hurricane Safety tips
There is no way to stop a hurricane or make it change direction, so if you ever find yourself in the path of a hurricane, be sure to remember the following safety tips.
＊ Be sure you have a radio, batteries, fresh drinking water, and enough food.
＊ Tell neighbors, friends, and family members your emergency (紧急的) plans. Tell them where you’ll go if you need to leave your home.
＊ If you live near the ocean, leave your home and travel to a safe place. You could stay with a friend or a family member, in a hotel, or in an emergency shelter area.
＊ Stay inside during the storm. You could be seriously injured (受伤的) if you go outside.
57. Are hurricanes storms?
58. Where do hurricanes happen?
59. What is the centre of a hurricane called?
60. What does the passage mainly talk about?
2.阅读短文，根据短文内容回答问题。（共10分，每小题2分）
We need to be responsible for our environment. Being a frugal consumer(节俭的消费者) is one way to help. But, what exactly does that mean?
Use It Up
You can use things up instead of wasting them. Squeeze that last bit of toothpaste out of the rube. Use the last little piece of soap. Don’t throw away any bits of the biscuit at the bottom of the box.
Wear It Out
You do not always need to have new things. Suppose your sneakers have broken laces, but they still fit you. Repair them and wear them longer. You don’t have to have the latest iPhone until the old one doesn’t work any more. Then you can get a new one. Think twice before replacing something that still works.
Make It Do
When something you want is not on hand, look for something else that you already have to take its place. Suppose you are packing your lunch for tomorrow and want a butter sandwich. You are out of butter. Have a cheese sandwich instead so that you can use all of the cheese. Learn to fix broken boys instead of just throwing them away. With a little thought, you can make something do, instead of buying something new.
Do Without
Think about all those things that you would like to have. Do you really need them? How long will you really play with that new toy you saw on TV? Making the things that we want uses up our world’s resources(资源). And, getting rid of the things we don’t want any more takes up even more resources and space.
65. Do we need to be responsible for our environment?
66. How do we deal with the last little piece of soap?
67. When do we need to get a new iPhone?
68. What should we do when something we want is not on hand?
69. What does the writer want to tell us?
3.阅读短文，根据短文内容回答问题。（共10分，每小题2分）
Chinatown is the name given to an area in the middle of London. It is just between Leicester Square and Shaftsbury Avenue. Gerrard Street is at the center and is the most important street in the area. There is a large Chinese community(社区) with a lot of Chinese restaurants, Chinese supermarkets and shops in this street.
In the 1950s, it was a poor area and everything was very cheap. At the same time, the world rice market changed and thousands of farm workers in Hong Kong lost their jobs. They began arriving in London to look for work. They found jobs in the restaurants in this area. Many British people liked Chinese food, and the restaurants were popular.
These restaurant workers often worked 17 hours a day and had no time to learn English. As more Chinese arrived, more shops and businesses grew up. Wives came and joined their husbands and children came and joined their fathers. The community grew, and Chinatown was born.
In the 1970s and 1980s, British-born Chinese started to have a better education and this brought economic(经济的) success to the area. Many families moved out of Chinatown, and there was more space for businesses. Gerrard Street became a street only for visitors and was soon a popular place for tourists.
Now everyone knows about London’s Chinatown. During the Chinese New Year, the streets are seen with flags and thousands of Chinese go into the streets. For most of the year, though, Londoners and tourists go there mainly for the food in the Chinese restaurants. The best restaurants are the ones where the Chinese eat.
65. Is this Chinatown in the middle of London?
66. Was the area rich or poor in the 1950s?
67. Why did the restaurant workers have not time to learn English?
68. When did British-born Chinese start to have a better education?
69. What are the main points about Chinatown in this passage?
4.阅读短文．根据短文内容回答问趣。（共10分，每小题2分）
Are you a twin? And if so, are you a "double" too? Then Ohio, the United States is the place for you to be for an August weekend of twin fun. Every year, in August, twins from all over the world get together in Ohio. for a special day -- the Twins Day Festival offered to twins and for a weekend of socially, celebration and fun.
The Twins Day Festival at Twinsburg is the world's largest gathering of twins every year. It's a big club-like event in which twins and their parents come to fins small town.
The first Twins Day Festival was held in 1976 with Only 37 pairs of twins, That year, the United States celebrated 200 years of independence, and then a group of people decided to set a day for twins. The directors did not want the festival to be a one-off celebration. So the next year, they planned it better and made sure that the festival continued at the same place. Since then, this festival has been held without fail, drawing twins from every corner of the world.
However, there used to be heated arguments whether Twins Day should be only a local celebration or a festival for children of multiple births. In 1979, the festival went international with two sets of twins arriving from Lebanon and Poland. In the same year, the Twins Day Committee was formed as a non-profit organization.
Today, the Twins Day Festival attracts 2,736 pairs of twins from every state in the USA and others from all over the world, from baby twins to people in their eighties and nineties!
65. Is the Twins Day Festival held in August every year?
66. Where is the world's largest gathering of twins held?
67. Why did the directors plan the festival better the next year？
68. when did the festival go international?
69. What are the main points about the Twins Day Festival in this passage?
5.阅读短文，根据短文内容回答问题。（共10分，每小题2分）
If you like unusual places, you should visit the Hebrides Islands. Not many people live on these islands in the northwest of Scotland. The land is not good for farming. It’s only good for keeping sheep. The winters are long, cold, and wet. It’s hard to make a living on the Hebrides, but for a visitor, these islands can be very special.
They’re not for everyone, however. Even summer days are cool and often windy. The water is too cold for swimming. There are no forests, and there are only a few trees and green fields. Instead of fields, there are just rocks and small plants. The hills, too, are just piles of rocks. Sometimes the view looks like pictures of the moon.
But there is beauty in this place. From the beach you can often see all the way to the rocky hills. From the hills you can see far out to other islands and the open ocean. The colors, too, are special. Blue is everywhere. It’s in the sky and in the ocean. It is in the tiny flowers that grow on the hills. In the spring there is also green in the hills. In the summer and fall the hills are more purple. Often the air is soft and gray with clouds and rain.
On these islands you can forget about the rest of the world. The evenings are quiet. The restaurants close early, and there isn’t any nightlife. Visitors stay at a guest house or a Bed and Breakfast. This is the best way to learn about life on the islands. The islanders are often friendly, and they like to talk.
If you want to meet islanders, you can also try the pubs（酒吧） or even the shops. People are in no hurry here. They like to chat about the weather or the fishing. There are also some tourist shops, but not many. They sell the usual tourist things. They also sell some beautiful clothes made of wool from the islands.
Do not come to the Hebrides for shopping. Come to walk in the clean, cool air. Come for the quiet beauty and for the views.
65. Are there many people living on the Hebrides Islands?
66. What’s the weather like on the Hebrides in the summer?
67. Where can you see other islands and the open ocean when you are on the Hebrides?
68. Where do visitors stay for the night on the Hebrides?
69. According to the passage, what can we do on the Hebrides?
6.阅读短文，根据短文内容回答问题。（共10分，每小题2分）
Peer pressure (同伴压力) can come to you in many shapes and sizes. We feel it from our peers to do certain things, dress certain ways, use certain words, eat certain foods, and on and on. No matter how old you are, there will always be peer pressure, but it can be a problem in high school. Though peer pressure can sometimes result in positive (积极的) results, usually it is used to describe a negative (消极的) influence.
Give in to Peer Pressure
Although everyone will probably give in to peer pressure at some time in their lives. Unluckily, there are people who are more likely to give in to negative peer pressure. They are the ones who show:
l Little or no self-confidence
l Loneliness
Common Activities Connected with Peer Pressure
The activities that your peers may pressure you to do are:
l Putting off school work to have fun
l Allowing others to cheat by copying your homework or exams
l Drinking and smoking
l Teasing (嘲弄) or bullying (欺侮) others
Defeating Peer Pressure
It takes courage! You need to develop the self-confidence, self-acceptance and self-love that will allow you to stay comfortable with your dreams and interests. The following suggestions can be helpful:
l Join groups whose members believe in the same things as you.
l Develop friendships with people who do not pressure you.
l Think about where you stand on issues so that you can give your own opinion.
l Discuss your opinions and future plans with your parents in order to get support.
Unfortunately, dealing with peer pressure seems to be part of being a teenager. Know yourself, love yourself and be yourself, and don't let anyone tell you differently!
65. Does peer pressure have negative influence?
66. What kind of teenagers is most likely to give in to peer pressure?
67. Will the negative pressure lead you to study harder or drink and smoke?
68. Why is it better for teenagers to talk to their parents?
69. What does the passage mainly talk about?
7.阅读与表达 (共10分，每小题2分)
阅读短文, 根据其内容回答问题。
For many of us the home in our hearts is one we remember from childhood(童年时期). For me it was the real house I ever lived in. The house had a big front yard with a swing(秋千) on it. Mary is my sister. We were both 8 years old at the time, but we weren’t twins. I in was January, and she in December. When it rained, we’d play there with neighbo