人教版九年级物理欧姆定律的知识点

《欧姆定律》

一、欧姆定律

1．探究电流与电压、电阻的关系

①提出问题：电流与电压电阻有什么定量关系？

②制定计划，设计实验：要研究电流与电压、电阻的关系，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。

③进行实验，收集数据信息：（会进行表格设计）

④分析论证：（分析实验数据寻找数据间的关系，从中找出物理量间的关系，这是探究物理规律的常用方法。）

⑤得出结论：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。

2．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。

3．数学表达式I=U/R。

4．说明：①适用条件：纯电阻电路（即用电器工作时，消耗的电能完全转化为内能）；

②I、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；

③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。

④是电阻的定义式，它表示导体的电阻由导体本身的长度、横截面积、材料、

温度等因素决定。

R＝U/I是电阻的量度式，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。

5．解电学题的基本思路。

①认真审题，根据题意画出电路图；

②在电路图上标出已知量和未知量（必要时加角码）；

③选择合适的公式或规律进行求解。

二、伏安法测电阻

1．定义：用电压表和电流表分别测出电路中某一导体两端的电压和通过的电流就可以根据欧姆定律算出这个导体的电阻，这种用电压表电流表测电阻的方法叫伏安法。

2．原理：I=U/R。

3．电路图：（如图）

4．步骤：①根据电路图连接实物。

连接实物时，必须注意开关应断开

②检查电路无误后，闭合开关S，三次改变滑动变阻器的阻值，分别读出电流表、电压表的示数，填入表格。

③算出三次Rx的值，求出平均值。

④整理器材。

5．讨论：⑴本实验中，滑动变阻器的作用：改变被测电阻两端的电压（分压），同时又保护电路（限流）。

⑵测量结果偏小是因为：有部分电流通过电压表，电流表的示数大于实际通过Rx电流。根据Rx=U/I电阻偏小。

⑶如图是两电阻的伏安曲线，则R1＞R2

三、串联电路的特点

1．电流：文字：串联电路中各处电流都相等。

字母：I=I1=I2=I3=……In

2．电压：文字：串联电路中总电压等于各部分电路电压之和。

字母：U=U1+U2+U3+……Un

3．电阻：文字：串联电路中总电阻等于各部分电路电阻之和。

字母：R=R1+R2+R3+……Rn

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．分压定律：文字：串联电路中各部分电路两端电压与其电阻成正比。

字母：U1/U2=R1/R2 U1：U2：U3：…=R1：R2：R3：…

四、并联电路的特点

1．电流：

文字：并联电路中总电流等于各支路中电流之和。

字母：I=I1+I2+I3+……In

2．电压：

文字：并联电路中各支路两端的电压都相等。

字母：U=U 1=U 2=U 3=……Un

3．电阻：

文字：并联电路总电阻的倒数等于各支路电阻倒数之和。

字母：1/R=1/R 1+1/R 2+1/R 3+……1/Rn

理解：把n 段导体并联起来，总电阻比任何一段导体的电阻都小，这相当于导体的横截面积增大。

特例：n 个相同的电阻R 0并联，则总电阻R=R 0/n 。

求两个并联电阻R 1．R 2的总电阻1212R R R R R =+

4．分流定律：文字：并联电路中，流过各支路的电流与其电阻成反比。

字母：I 1/I 2=R 2/R 1

赠送以下资料

英语万能作文(模板型）

Along with the advance of the society more and more problems are brought to our attention, one of which is that....

随着社会的不断发展，出现了越来越多的问题，其中之一便是

____________。

As to whether it is a blessing or a curse, however, people take different attitudes.

然而，对于此类问题，人们持不同的看法。(Hold different attitudes 持不同的看;Come up with different attitudes 有不同的看法)

As society develops, people are attaching much importance to....

随着社会的发展，人们开始关注............

People are attaching more and more importance to the interview during job hunting

求职的过程中，人们慢慢意识到面试的重要性。

As to whether it is worthwhile ....., there is a

long-running controversial debate. It is quite natural that people from different backgrounds may have divergent attitudes towards it.

关于是否值得___________的问题，一直以来争论不休。当然，不同的人对此可能持不同的观点。

In the process of modern urban development, we often find ourselves in a dilemma.

在都市的发展中，我们往往会陷入困境。

Recently the phenomenon has aroused wide concern, some people are in alarm that....

最近，这种现象引起了人们的广泛关注，有人开始担心

______________。

The human race has entered a completely new stage in its history, with the increasingly rapid economic globalization and urbanization, more problems are brought to our attention.

人类进入了一个历史的崭新的阶段，经济全球化、都市化的速度不断加快，随之给我们带来了很多问题。

...... plays such an important role that it undeniably becomes the biggest concern of the present world, there comes a question, is it a blessing or a curse?"

_______显得非常重要而成为当今世界所关注的最大的问题，这是无可厚非的。不过，问题是："我们该如何抉择?"

Now we are entering a new era, full of opportunities and challenges,

现在我们正在进入一个充满机会和挑战的新时代。

People from different backgrounds would put different interpretations on the same case.

不同行业的人对同一种问题的解释不尽相同。

The controversial issue is often brought into public focus. People from different backgrounds hold different attitudes towards the issue.

这中极具争议性的话题往往很受社会的关注。不同的人对此问题的看法也不尽相同。

When asked ..., some people think..... while some prefer...

说到______，有人认为________，而另一些人则认为__________。

Just as the saying goes: "so many people, so many minds". It is quite understandable that views on this issue vary from person to person.

俗话说，""。不同的人对此有不同的看法是可以理解的。

To this issue, different people come up with various attitudes.

对于这个问题，不同的人持不同的观点。

There is a good side and a bad side to everything, it goes without saying that...

万事万物都有其两面性，所以，勿庸置疑，____________。

When it comes to ..., most people believe that ..., but other people regard ...as ....

提到_________问题，很多人认为_________，不过，一些人则认为______是____.

When faced with...., quite a few people claim that ...., but other people think as...

提到_________问题，仅少数人认为________，但另一些人则认

为_________。

There is a public controversy nowadays over the issue of .... There who criticize ...argue that ...., they believe

that ...,but people who favor .., on the other hand, argue that...

目前，____问题争议较大。批判_____的人认为_____，他们认为_____，不过，另一方面，赞同_____的人则认为_______。

Some people are of the opinion that.. 有些人认为

_________。

Many people claim that... 很多人认为_________。

A majority of 绝大多数

A large number of 很多人

Some people contend that ... has proved to bring many advantages (disadvantages)

有些人认为________有很多有利之处(不利之处)。

Those who argue for ... say that ...economic development of the cities.

觉得_____的人认为，______ 城市的经济发展。

Some people advocate that ....

有些人在坚持认为_________。

They hold that ... 他们认为_________。

People, who advocate that ..., have their sound reasons (grounds)

坚持认为______的人也有其说法(依据)。

Those who have already benefited from practicing it sing high praise of it. 那些从中受益的人对此大家褒奖。

Those who strongly approve of ... have cogent reasons for it.

强烈认同_______的人有很多原因。

Many people would claim that... 有人会认为___________。

People who support ... give some or all of the following reasons.

那些支持_________观点的人列出了如下原因：________。

But others hold the view that ...但是，另外一些人则认为

_______。

观点的用词：Attitude, opinion, 与其搭配的动词以及词组：Take, have, come up with，set forth, put forward等。

But on the other hand, there are also quite a few people who strongly advocate that..,.

不过，另一方面，也有少部分人坚持认为_______________。

But people who are ..., on the other hand , maintain that...

不过，另一方面，________的人认为__________。

However, there are a large number of people who hold a different view concerning this case.

然而，很多人对此有不同的看法。

问题用词：Issue, phenomenon，后接介词, on, over等。

However, some others argue that... 然而，另一些人则认为____。

However, there are also some others who contend that...

然而，也有人认为__________。

But other people set forth completely totally different argument concerning this case.

不过，对于此，另一些人则持完全不同的观点。

Some people examine this issue from another angle.

有的人用另一角度来看这一问题。

On the other hand, there are also many opponents who

strongly ...

另一方面，也有很多反对的人，他们认为_____________。

According to my personality and fondness, I would prefer ... rather than...

根据我的个性以及兴趣，我选择_______而不会选择__________。

Personally, I side with the latter (former) opinion...

就我个人而言，我支持后者(前者)___________。

Personally, I am in favor of the former point of view.

就我个人而言，我较同意前一种看法。

To my point of view 我认为

To my mind, the advantages far overweigh the

drawbacks(disadvantages, shortcomings)

我认为，优点胜过缺点。

For my part, I stand on side of the latter opinion that..

就我而言，我较赞同后一种观点________________。

As far as I am concerned, I am inclined to be on the side of the latter view.

在我看来，我较同意后一种观点。

After a thorough consideration, for my part, I am in favor of the latter view that...

经过深思熟虑，我较支持后一种看法，亦即___________。

If asked to make a decision, I would prefer...

如果真的需要作出选择，我宁愿____________。

展现问题篇

问题的常用词：question, problem, issue

Recently, the issue of ...... has been brought into public focus.

近来，_______的问题引起了社会的广泛关注。

Now we are entering a brand new era full of opportunities and innovations, and great changes have taken place in people’s attitude towards some traditional practice.

现在我们进入了一个充满机遇和创新的崭新时代，很多人对某些传统的看法也发生了很大改变。

Recently the issue of whether or not ... has been in the limelight and has aroused wide concern in the public.

近来，是否____的问题已经非常明确而且引起了社会的广泛关注。

The issue whether it is good or not to .... has aroused a heated discussion all over the country.

______的利与弊已在全国范围内引起热烈的讨论。

At present, some people think ....while others

claim ...Both sides have their merits.

目前，一些人认为_____而另一些人则认为_____。其实，两种观点都其可取之处。

People rarely reach an absolute consensus on such a controversial issue.

对于这种极具争议的话题，我们很难作出绝对的回答。

People from different backgrounds would put different interpretations on the same case.

不同行业的人对同一种问题的解释不尽相同。

The controversial issue is often brought into public focus. People from different backgrounds hold different attitudes towards the issue.

这中极具争议性的话题往往很受社会的关注。不同的人对此问题的看法也不尽相同。

When asked ..., some people think..... while some prefer...

说到______，有人认为________，而另一些人则认为__________。

Just as the saying goes: "so many people, so many minds". It is quite understandable that views on this issue vary from person to person.

俗话说，""。不同的人对此有不同的看法是可以理解的。

To this issue, different people come up with various attitudes.

对于这个问题，不同的人持不同的观点。

There is a good side and a bad side to everything, it goes without saying that...

万事万物都有其两面性，所以，勿庸置疑，____________。

When it comes to ..., most people believe that ..., but other people regard ...as ....

提到____问题，很多人认为____，不过，一些人则认为____是____. When faced with...., quite a few people claim that ...., but other people think as...提到___问题，仅少数人认为___，但另一些人则认为____.