问题 选择题

在蹄形磁铁的上方用橡皮绳悬挂一根通电直导线CD,电流的方向如图所示,在磁场力的作用下,直导线CD将(    )

A.向下平动,橡皮绳再伸长一些

B.向纸面外平动,橡皮绳再伸长一些

C.C端向纸面外转动,D端向纸里转动,橡皮绳再伸长一些

D.D端向纸面外转动,C端向纸里转动,橡皮绳缩短一些

答案

答案:C

考点:

专题:受力分析方法专题.

分析:采用电流元法,将直导线分为左右两部分研究,根据左手定则,判断出图示位置导线左部所受安培力向外,右部向内;考虑特殊位置,若导线转过90°时,安培力向下.则导线在逆时针方向旋转的同时向下运动,根据牛顿第三定律,磁铁受到向上的安培力向上,则可确定地面对磁铁的支持力是减小的.

解答:解:由于导线左右两部分处在的磁场方向不同,可采用电流元法,即将直导线分为左右两部分处理,根据左手定则,判断出图示位置导线左部所受安培力向外,右部向内;又考虑特殊位置:导线转过90°时,安培力向下.则俯视,导线在安培力作用下,逆时针方向旋转的同时向下运动,即C端向纸面外转动,D端向纸里转动,橡皮绳再伸长一些,故C正确

故应该选C

点评:判断在安培力作用下导体的运动方向是常见题型,常用方法有电流元法、特殊位置法、等效法等.

阅读理解

Everyone has good days and bad days.

Sometimes, you feel as if you’re on top of the world. But occasionally you feel horrible, and you lose things and you cannot focus on your schoolwork.

For more than 20 years, scientists have suggested that high self-esteem (自尊) is the key to success. Now, new research shows that focusing just on building self-esteem may not be helpful. In some cases, having high self-esteem can bring bad results if it makes you less likeable or more upset when you fail at something.

“Forget about self-esteem,” says Jennifer Crocker, a psychologist (心理学家) at the University of Michigan, US. “It’s not the important thing.”

Feeling good

Crocker’s advice may sound a bit strange because it is good to feel good about yourself.

Studies show that people with high self-esteem are less likely to be depressed, anxious, shy, or lonely than those with low self-esteem.

But, after reviewing about 18,000 studies on self-esteem, Roy Baumeister, a psychologist at Florida State University, has found that building up your self-esteem will not necessarily make you a better person.

He believes that violent and wicked people often have the highest self-esteem of all. He also said: “There’s no evidence that kids with high self-esteem do better in school.”

Problems

All types of people have problems. People with high self-esteem can have big egos (自我) that can make them less likeable to their peers(同龄人), said Kathleen Vohs, a psychology professor at Columbia University.

People with high self-esteem tend to think more of themselves, Vohs says. People with low self-esteem are more likely to rely on their friends when they need help.

What to do

Researchers say it is best to listen to and support other people. Find positive ways to contribute to society. If you fail at something try to learn from the experience. “The best therapy (药方) is to recognize your faults,” Vohs says. “It’s OK to say, ‘I’m not so good at that,’ and then move on.”

小题1:The new research comes to the conclusion that high self-esteem ________.

A.is not important at all

B.has taken on a different meaning

C.may not be the key to success

D.does not help you do better at school小题2:One of the conclusions of the new research is that ________.

A.feeling good about oneself doesn’t mean you lead a happier life

B.people with high esteem usually do not seek other’s help

C.people with high esteem tend to be proud

D.people with low esteem are often more popular小题3:The underlined part “a better person” in the passage probably means a person who is ________.

A.helpful and supportive

B.gentle and modest

C.likable and successful

D.friendly and kind小题4:From the text, we can infer the best therapy mentioned in the last paragraph is mainly for people ________.

A.with high self-esteem

B.with low self-esteem

C.of all kinds

D.who are focusing on building self-esteem

填空题