问题 问答题

如图是一个中间有抽头的电磁铁的示意图,小明为了研究外形相同的电磁铁磁性的强弱与通电电流的大小及线圈匝数的关系,他做了如下实验,实验步骤为:

(1)先连接好如图甲所示的电路图,调整滑动变阻器的滑片使电流表示数减小,记为I1,发现电磁铁吸引的大头针的数目较少;

(2)调整滑动变阻器滑片使电流表的示数增大到I2,发现电磁铁吸引住的大头针数目增加;

(3)再照图乙所示的电路图连接的电路,调整滑动变阻器的滑片使电流表的示数保持为I2,发现电磁铁上吸引住大头针的数目进一步增加.

从以上实验我们得出的结论是:

①______;

②______.

(4)在实验步骤(3)中为什么要强调电流表的示数与步骤(3)中电流表示数(I2)保持相同?

答:______.

答案

①(1)和(2)控制的是线圈匝数一定,研究电磁铁磁性强弱与电流大小的关系.当电流增大时,电磁铁吸引的大头针数目增多,表明磁性增强.结论:线圈匝数一定时,电流越大,电磁铁磁性越强;

②(2)和(3)控制的是电流一定,研究电磁铁磁性强弱与线圈匝数多少的关系.当线圈匝数增多时,电磁铁吸引的大头针数目增多,表明磁性增强.结论:电流一定时,线圈匝数越多,电磁铁磁性越强.

(4)因为电磁铁磁性强弱与电流大小和线圈匝数都有关系,所以在研究磁性强弱与线圈匝数的关系时,就一定要保证在电流一定的条件下去研究.

故答案为 (3)①线圈匝数一定时,电流越大,电磁铁磁性越强;②电流一定时,线圈匝数越多,电磁铁磁性越强.

(4)保证在电流一定的条件下,研究电磁铁磁性强弱与线圈匝数的关系.

完形填空

What is language for? Some people seem to think it’s for practicing grammar rules and learning lists of words. That’s wrong. Language is for exchange of ideas, for communication.

The way to learn a language is to practice speaking it as often as possible. A great man once said it is necessary to practice as much as possible. And the more you use it in real situations, the more natural it will become.

Learning any language takes a lot of effort. But don’t give up. Relax! Be patient and enjoy yourself. Learning foreign languages should be fun. Rome wasn’t built in a day. Work harder and practice more. Your hard work will be rewarded by God one day. God is equal to everyone!

Use a dictionary and a grammar guide constantly(不断地). Keep a small English dictionary with you at all time. When you see a new word, look it up. It can help you. Think about the word—use it, in your hand, in a sentence.

Try to think in English whenever possible. When you see something, think of the English word, then think about the word in a sentence.

Practise tenses as many as possible. When you learn a new verb, learn its various forms.

Learn more about the culture behind the language. When you understand the cultural background, you can better use the language.

阅读以上信息,完成下面的句子,每空一词。

小题1:It’s not        for some people to think language is for practicing grammar rules and learning lists of words.

小题2:If you work harder and practice more, God will          you in some way.

小题3:A dictionary is a good        when you don’t know how to use a new word.

小题4:When you learn a verb, pay attention to the different         of it.

小题5:Besides the language,         background learning is necessary.

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