问题 选择题

一平面线圈用细杆悬于P点,开始时细杆处于水平位置,释放后让它在如图所示的匀强磁场中运动.已知线圈平面始终与纸面垂直,当线圈第一次通过位置B和位置C的过程中,下列对磁通量变化判断正确的是(   )

A.一直变大

B.一直变小

C.先变大后变小

D.先变小后变大

答案

答案:C

题目分析:由图可知,线圈由A经过B到C的过程中,线圈垂直磁场方向的面积先增大后减小,通过线圈的磁通量为,可见通过线圈的磁通量先变大后变小。

故选C

点评:当面积S和匀强磁场方向垂直时,不垂直应取垂直于磁场方向的有效面积。

阅读理解

Do you want to live with a strong sense of peacefulness, happiness, goodness, and self- respect? The collection of happiness actions broadly categorized as "honor" help you create this life of good feelings.

Here's an example to show how honorable actions create happiness.

Say a store clerk fails to charge us for an item. If we keep silent, and profit from the clerk's mistake, we would drive home with a sense of sneaky excitement. Later we might tell our family or friends about our good fortune. On the other hand, if we tell the clerk about the uncharged item, the clerk would be grateful and thank us for our honesty. We would leave the store with a quiet sense of honor that we might never share with another soul.

Then, what is it to do with our sense of happiness?

In the first case, where we don't tell the clerk, a couple of things would happen. Deep down inside we would know ourselves as a type of thief. In the process, we would lose some peace of mind and self-respect. We would also demonstrate that we cannot be trusted, since we advertise our dishonor by telling our family and friends. We damage our own reputations by telling others. In contrast, bringing the error to the clerk's attention causes different things to happen. Immediately the clerk knows us to be honorable. Upon leaving the store, we feel honorable and our self-respect is increased. Whenever we take honorable action we gain the deep internal rewards of goodness and a sense of nobility.

There is a beautiful positive cycle that is created by living a life of honorable actions. Honorable thoughts lead to honorable actions. Honorable actions lead us to a happier existence. And it's easy to think and act honorably again when we're happy. While the positive cycle can be difficult to start, once it's started, it's easy to continue. Keeping on doing good deeds brings us peace of mind, which is important for our happiness.

小题1:According to the passage, the positive action in the example contributes to our ________.

A.self-respect

B.financial rewards

C.advertising ability

D.friendly relationship小题2:The phrase "bringing the error to the clerk's attention" (in Para.5) means ________.

A.telling the truth to the clerk

B.offering advice to the clerk

C.asking the clerk to be more responsible

D.reminding the clerk of the charged item小题3:How will we feel if we let the clerk know her mistake?

A.We'll be very excited.

B.We'll feel unfortunate.

C.We'll have a sense of honor.

D.We'll feel sorry for the clerk.小题4:Which of the following can be the best title of this passage?

A.How to Live Truthfully

B.Importance of Peacefulness

C.Ways of Gaining Self-respect

D.Happiness through Honorable Actions

名词解释