问题 选择题

如图所示的是A、B、C三个用细线悬挂的轻质小球,靠近时发生相互作用的情形,关于各小球带电的判断,下列说法中正确的是

A.可能A带负电,B带正电,C带负电     

B.可能A带负电,B不带电,C带正电

C.可能A带正电,B带正电,C不带电     

D.可能A不带电,B带负电,C带正电

答案

答案:C

题目分析:利用电荷间的作用规律分析即可,但应注意的是:若两小球相斥,则表明其一定都带电,且带的是同种电荷;若两小球相吸,则有两种可能,即可能都带电,且是异种电荷,也可能一个带电,另一个不带电。由于A、B两小球相斥,即说明A、B一定都带电,且带的是同种电荷,故该题有两种可能:若A球带正电,即B球也带正电,由于B、C相吸,故C球有两种可能,即C球可能带负电,也可能不带电;若A球带负电,即B球也带负电,由于B、C相吸,故C球也是两种可能,即C球可能带正电,也可能不带电。

故选C。

点评:此题很容易漏掉了带电体具有吸引轻小物体的性质的这种情况。

单项选择题

阅读下列短文,从每题所给的四个选项(A、B、C和D)中,选出最佳选项,并在答题卡上将该项涂黑。

B

Five years ago, when I taught art at a school in Seattle, I used Tinkertoys as a test at the beginning of a term to find out something about my students. I put a small set of Tinkertoys in front of each student, and said:”Make something out of the Tinkertoys. You have 45 minutes today - and 45minutes each day for the rest of the week.”

A few students hesitated to start. They waited to see the rest of the class would do. Several others checked the instructions and made something according to one of the model plans provided. Another group built something out of their own imaginations.

Once I had a boy who worked experimentally with Tinkertoys in his free time. His constructions filled a shelf in the art classroom and a good part of his bedroom at home. I was delighted at the presence of such a student. Here was an exceptionally creative mind at work. His presence meant that I had an unexpected teaching assistant in class whose creativity would infect(感染) other students.

Encouraging this kind of thinking has a downside. I ran the risk of losing those students who had a different style of thinking. Without fail one would declare, ” But I’m just not creative.”

“Do you dream at night when you’re asleep?”

“Oh, sure.”

“So tell me one of your most interesting dreams.” The student would tell something wildly imaginative. Flying in the sky or in a time machine or growing three heads. “That’s pretty creative. Who does that for you?”

“Nobody. I do it.”

“Really-at night, when you’re asleep?”

“Sure.”

“Try doing it in the daytime, in class, okay?”

Why did the teacher ask the students to talk about their dreams?()

A. To help them to see their creativity.

B. To find out about their sleeping habits.

C. To help them to improve their memory.

D. To find out about their ways of thinking.

判断题