问题 选择题

如图18-1-8所示,甲、乙、丙、丁四个LC振荡电路中,某时刻振荡电流i的方向如箭头所示.下列对各回路情况的判断正确的是(    )

图18-1-8

A.若甲电路中电流i正在增大,则该电路中线圈的自感电动势必定在增大

B.若乙电路中电流i正在增大,则该电路中电容器里的电场方向必定向下

C.若丙电路中电流i正在减小,则该电路中线圈周围的磁场必在增强

D.若丁电路中电流i正在减小,则该电路中电容器极板电荷必是上负下正

答案

BD

如果i正在增大,则其变化率一定在减小,故自感电动势一定在减小;若i在减小,则线圈周围的磁场一定在减弱,故首先可以排除A、C.若i在增大,说明是放电过程,对于乙图,是从上极板流向下极板,则说明上极板带正电,进而可判断电场方向必向下,故B对.若i在减小,则说明是充电过程,在丁图中,电流指向下极板,故下极板必充上正电,上板带负电,所以D正确.

阅读理解

Anne Sanders was practicing soccer moves, which was not normal. Usually, Anne only plays basketball. She wins every basketball game she plays, and she loses at any other game.  "Anne", I waved to her. "Why are you playing soccer?"

"Well, the gym teacher is doing something different," she said. "There are teams of four and partners of two.We get to pick our partners, and I want someone to pick me. "Anne held up a list.

"It looks like I'm on a team with you, Stacey, and Paul," I said.  "Stacey is my best friend.Maybe we can be together: " Just then,  Stacey and Paul came over.  They had heard of the teams.

"Do you want to be partners, Stacey?" I asked.

"Well, I was going to be partners with Paul," she claimed. I didn't blame her. Paul was as fast as a rocket, and my nickname was "Snail".  "But we are best friends," said Stacey.  “So I guess I'II be with you. "

It was our first game. Stacey went to talk to some other friends afterwards, and Paul and Anne were talking about winning their game. I was sipping on my water, when I overheard Stacey, "She's worse than I thought; if I played the team alone,, I would have won easily. She's worse than a snail.  She's more like a statue. "

That night, I felt terrible for losing and mad at Stacey for calling me a statue. After all, she was my best friend and my only friend. Anyway, the phone rang, and it was Stacey. At first, I thought she might apologize, but no such luck.

“Allison,  the game tomorrow is canceled, "  she said.

"Okay," I replied.  "Sorry about the game today", Stacey hung up on me.

The next day, I went over to the soccer field. I knew the game was canceled, but maybe I could help clean up.But instead of a mess, I saw a soccer game in progress.  Stacey and were playing, and Anne was hiding in the corner.  "Paul made me pretend to be sick, "  she whispered.  “He wants to play with Stacey because she's so fast. "

So Anne and I went to get ice cream.  Even if I lost Stacey ,I just created a lifelong friendship.

小题1:Why did Anne practice playing soccer?

A.Because she wanted to win in all games.

B.Because she didn't want to be left out.

C.Because she intended to be a normal student.

D.Because she hoped to do something different.小题2:What did Stacey complain about Allison?

A.Allison called her nickname.

B.Allison was as fast as a rocket.

C.Allison didn't treat her as a best friend

D.Allison moved too slowly in the game.小题3:Stacey phoned Allison in order to

A.get rid of Allison as a partner

B.apologize for calling Allison a statue

C.tell Allison there was no game tomorrow

D.encourage Allison to fight in the next game小题4:Allison went to the soccer field to________

A.watch a soccer game

B.keep the soccer field clean

C.find out Why the game was cancelled

D.make preparations for another game小题5:What conclusion can we draw from this passage?

A.Allison wanted to be partners with Anne.

B.Stacey called Allison to show real concern.

C.Allison and Anne would be friends forever.

D.Anne was hiding in the corner because she was sick.

单项选择题