第七章 欧姆定律 重要笔记
一， 探究电流与电压、电阻的关系。
①采用的研究方法是：控制变量法。即：保持电阻不变，改变电压研究电流随电压的变化关系；保持电压不变，改变电阻研究电流随电阻的变化关系。
②结论：在电阻一定的情况下，导体中的电流与加在导体两端的电压成正比；
在电压不变的情况下，导体中的电流与导体的电阻成反比。
二、欧姆定律的内容：导体中的电流，跟导体两端的电压成正比，跟导体的电阻成反比。
1、数学表达式 I=U/R
2、说明： ① I、U、R对应同一导体或同一段电路，不同时刻、不同导体或不同段电路三者不能混用，应加角码区别。三者单位依次是 A 、V 、Ω
② 同一导体（即R不变），则I与U 成正比； 同一电源（即U不变），则I 与R成反比。
③ R＝U/I 是电阻的计算式，它表示导体的电阻可由U/I给出，即R 与U、I的比值有关，但R与外加电压U 和通过电流I等因素无关。
三、串联电路的特点（重点）：分压同流
1、电流：串联电路中各处电流都相等。
I=I1=I2
2、电压：串联电路中总电压等于各部分电路电压之和。
U=U1+U2
3、电阻：串联电路中总电阻等于各部分电路电阻之和。
R=R1+R
理解：把n段导体串联起来，总电阻比任何一段导体的电阻都大，这相当于增加了导体的长度。
特例: n个相同的电阻R0串联，则总电阻R=nR0 .
4、分压规律：串联电路中各部分电路两端电压与其电阻成正比
U1/U2=R1/R2 ， U1/U总=R1/R总
四、并联电路的特点（重点）：分流同压
1、电流： 并联电路中总电流等于各支路中电流之和。
I=I1+I2
2、电压：
并联电路中各支路两端的电压都相等。
U=U1=U2
3、电阻：
并联电路总电阻的倒数等于各支路电阻倒数之和（不要求掌握）
1 8A U1~U2月考复习归纳之一——易错词
1. true
2. sense
3. worst
4. height
5. magazine
6. humorous
7. competition
8. smiling
9. excellent
10. vacation
11. language
12. through
13. physics
14. foreign
15. advertisement
8A U1~U2月考复习归纳之二——重点词组
1. tell lies
2. one of my best friends
3. have a good sense of humour
4. feel bored/excited
5. keep a secret
6. make friends with
7. listen to people carefully
8. travel around the world
9. some day
10. on Friday afternoon
11. what else
12. wear uniforms
13. do morning exercises
14. at most
15. look through the questions quickly ☆
16. at lunchtime
17. an hour of homework
8年上册新目标Units1-2基础知识专练
词汇
I. 根据句意及汉语提示写出正确的单词。
1. I looked for my pen everywhere, but I couldn’t find it ________ (任何地方).
2. ________(大多数) of my classmates think exercising is good for their body.
3. It’s a good habit to keep a (日记) in English.
4. Jack, __________(某人) wants to meet you.
5. There are many after-school ___________(活动) in our school.
6. His uncle went to Africa as a ________(商人) last year.
7. Jim’s home is not far from school. He always rides his _______(自行车) to school.
8. The ________(牙医) told the boy not to eat too many candies.
9. Jane usually put some milk into her_______(咖啡).
10. There are some _________(杂志) about science in the library.
II. 根据句意及首字母提示补全下列单词。
1. The boy t cooking by himself when his parents were away.
2. The doctor said he could do n
to save the child.
广东省深圳高级中学2020第二学期牛津深圳版
英语八年级下 U1-U2单元测试卷
班级 姓名 分数
I. 单项选择（共35小题，每小题1分，共35分）
i. 从下面每小题的A、B、 C三个选项中选出可以替换划线部分的最佳选项。
( )1. I enjoy reading because it gives me knowledge and brings me joy.
A. sadness B. happiness C. surprise
( )2.—What does the expression on his face mean?
—It means he is very happy.
A. look B. sound C. thought
( )3. —I reminded you about the party today, but you still forgot it.
—I’m very sorry for that.
A. made ... leave B. made ... organize C. made ... remember
( )4. —Don’t worry. I believe nothing will take place because we’ve been ready for everything.
—That’s good. But we’d better be careful.
A. happen B. matter C. change
( )5. —Look at me, Doris. Raise your spirits and everything will be OK.
—You’re right. I should be confident.
