问题 选择题

如图所示,矩形线圈abcd与可变电容器C、理想电流表A组成闭合电路。线圈在有界匀强磁场中绕垂直于磁场的bc边匀速转动,转动的角速度ω=100π rad/s。线圈的匝数N=100,边长ab=0.2m、ad=0.4m,电阻不计。磁场只分布在bc边的左侧,磁感应强度大小B=T。电容器放电时间不计。下列说法正确的是

A.该线圈产生的交流电动势峰值为50 V

B.该线圈产生的交流电动势有效值为25V

C.电容器的耐压值至少为50V

D.电容器的电容C变大时,电流表的示数变小

答案

答案:B

该线圈产生的交流电动势峰值为NBSω=100××0.2×0.4×100π=50V,选项A错误;由502×T/2R=E2T/R解得该线圈产生的交流电动势有效值为25V,选项B正确;电容器的耐压值至少为50V,选项C错误;电容器的电容C变大时,容抗减小,电流表的示数变大,选项D错误。

阅读理解

Bowing is a very important custom in Japan. Unlike people in many other countries, they greet each other by bowing instead of shaking hands. It is impolite not to return a bow to whoever bows to you.

Bowing has many functions in one. It expresses the feeling of respect, thanks, regret, and so on. You can bow when you say, “thank you”, “sorry”, “hello”, “goodbye”, “congratulations”, “excuse me”, “good morning”, and more.

Bowing seems simple, but there are different ways of bowing. Bowing techniques vary from a small nod of the head to a long, 90-degree bow. It depends on the social position or age of the person you bow to. If your opposite is of higher social position or older than yourself, you are supposed to bow deeper and longer than him or her. It is polite to bow from your waist. Men usually keep their hands at their sides, and women usually put their hands together on their legs with their fingers touching. If it is not a very formal situation, you can bow by nodding. The most common bow is a bow of about 15 degrees.

You might feel strange doing it, but try to bow in Japan. You will be considered very polite!

小题1:The author writes the passage mainly to _____.

A.introduce the history of bowing in Japan

B.describe the purposes of bowing in Japan

C.describe different ways of bowing in Japan

D.introduce the Japanese custom of bowing小题2:By saying “Bowing has many functions in one”, the author means that _____.

A.one kind of bow has many similar functions

B.people can express different feelings by bowing

C.people bow to express their feelings

D.the more times you bow, the more respect you receive小题3:How people greet in many countries?

A.by bowing

B.by shaking hands

C.by kissing each other

D.by touching小题4:If an assistant wants to show respect to her professor, she may bow like _____.

A            B          C           D

单项选择题