关于电场和电场线的提出，以下说法正确的是[ ] A．库仑提出

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问题不定项选择

关于电场和电场线的提出，以下说法正确的是 [ ]

A．库仑提出了电场的概念

B．法拉第提出了电场的概念

C．库仑提出用电场线描述电场

D．法拉第提出用电场线描述电场

答案

句型转换

根据要求完成句子。

1. We publish our school newspaper twice a month. (改为被动语态)

Our school newspaper ______ ______ twice a month.

2. The meeting began half an hour ago. (同义句)

The meeting has ______ ______ for half an hour.

3. I heard that she was singing at that time. (改为简单句)

I heard ______ ______ at that time.

4. My brother gave my mother a present on her birthday. (改为被动语态)

A present ______ ______ to my mother on her birthday.

5. My friend seems to be very angry. (同义句)

______ seems that my friend ______ very angry.

计算题

（8分）如图所示，两端开口的U形玻璃管两边粗细不同，粗管横截面积是细管的2倍。管中装入水银，两管中水银面与管口距离均为，大气压强为。现将粗管管口封闭，然后将细管管口用一活塞封闭并将活塞缓慢推入管中，直到两管中水银面高度差达到为止。整个过程中气体温度保持不变，求：

①左端液面下降多少？ ②活塞下移的距离(结果保留两位有效数字)。