问题 选择题

对于库仑定律,下面说法中正确的是(  )

A.凡计算两个带电体间的相互作用力,就可以使用公式F=

KQ1Q2
r2

B.两个点电荷之间的距离趋于零时,它们之间的库仑力将趋于无穷大

C.真空中相互作用的两个点电荷,不论它们电量是否相同,它们受到的库仑力大小一定相等

D.库仑定律适用于点电荷,点电荷其实就是体积很小的带电体

答案

A、库仑定律的适用条件是:真空和静止点电荷,故A错误;

B、当两个点电荷距离趋于0时,两电荷不能看成点电荷,此时库仑定律的公式不再适用.故B错误.

C、真空中相互作用的两个点电荷,不论它们电量是否相同,它们受到的库仑力大小一定相等,故C正确,

D、当带电体的形状、大小及电荷的分布状况对它们之间的作用力影响可以忽略时,可以看成点电荷.不是体积小就能看成点电荷.故D错误.

故选C.

阅读理解

Baekeland and Hartmann report that the “short sleepers” had been more or less average in their sleep needs until the men were in their teens. But at about age 15 or so, the men voluntarily began cutting down their nightly sleep time because of pressures from school, work, and other activities. These men tended to view their nightly periods of unconsciousness as bothersome interruptions in their daily routines.

In general, these “short sleeps” appeared ambitious, active, energetic, cheerful, conformist(不动摇) in their opinions, and very sure about their career choices. They often held several jobs at once, or workers full-or part-time while going to school. And many of them had a strong urge to appear “normal” or “acceptable” to their friends and associates.

When asked to recall their dreams, the “short sleepers” did poorly. More than this, they seemed to prefer not remembering. In similar fashion, their usual way of dealing with psychological problems was to deny that the problem existed, and then to keep busy in the hope that the trouble would go away.

The sleep patterns of the “short sleepers” were similar to, but less extreme than, sleep patterns shown by many mental patients categorized as manic(疯人).

The “long sleepers” were quite different indeed. Baekeland and Hartmann report that these young men had been lengthy sleeps since childhood. They seemed to enjoy their sleep, protected it, and were quite concerned when they were occasionally deprived of their desired 9 hours of nightly bed rest. They tended to recall their dreams much better than did the “short sleepers.”

Many of the “long sleepers” were shy, anxious, introverted (内向), inhibited (压抑), passive, mildly depressed, and unsure of themselves (particularly in social situations). Several openly state that sleep was an escape from their daily problems.

64. According to the report,______.

A) many short sleepers need less sleep by nature

B) many short sleepers are obliged to reduce their nightly sleep time because they are busy with their work

C) long sleepers sleep a longer period of time during the day

D) many long sleepers preserve their sleeping habit formed during their childhood

65. Many “short sleepers” are likely to hold the view that _____.

A) sleep is a withdrawal from the reality

B) sleep interferes with their sound judgement

C) sleep is the least expensive item on their routine program

D) sleep is the best way to deal with psychological troubles

66. When sometimes they cannot enjoy adequate sleep, the long sleepers might ____.

A) appear disturbed

B) become energetic

C) feel dissatisfied

D) be extremely depressed

67. Which of the following is Not included in the passage?

A) If one sleeps inadequately, his performance suffers and his memory is weakened

B) The sleep patterns of short sleepers are exactly the same as those shown by many mental patients

C) Long and short sleepers differ in their attitudes towards sleep

D) Short sleepers would be better off with more rest

单项选择题