问题 选择题

关于电场力和电场强度,下列说法正确的是(  )

A.电场强度的方向总是跟电场力的方向一致

B.电场强度的大小总是跟电场力的大小成正比

C.正电荷受到的电场力的方向跟电场强度的方向一致

D.电荷在某点受到的电场力大,说明该点的电场强度大

答案

A、C、电场强度的方向规定与放在该点的正的试探电荷所受电场力方向一致,与负的试探电荷所受电场力方向相反,故A错误,C正确;

B、D、只要有电荷存在就有静电场存在,电场的存在与否是客观的,与是否引入试探点电荷无关;引入试探点电荷只是为了检验电场的存在和讨论电场的性质而已;正像人们使用天平可以称量出物体的质量,如果不用天平去称量物体时,物体的质量仍然是客观存在的一样,故B错误,D错误;

故选C.

单项选择题

For some people, the light of human attention has an unbearable brilliance. Like ivy along the dim edge of a garden, they prefer the social shadows, shunning parties, publicity and fame of any sort. Then there are the flowers of the human arboretum. For them, being in the view of others seems necessary for life itself. From Hollywood to fabricated prime-time reality, this spotlight-dependent species is thriving.

But what about the individuals who crave attention for more desperate reasons Those who resort to unusual ways to get it Lately, it seems, a dark bloom of these characters has emerged. For motives known only to themselves, they have won notoriety by drawing on an almost sacred well of social status, victim hood.

In early April, US national news outlets tracked the disappearance of Audrey Seiler, a sophomore at the University of Wisconsin in Madison. Police and hundreds of concerned citizens searched for four days before Seiler was discovered. Seiler said she was kidnapped. Within hours, however, her story fell apart. Police announced that her abduction had been a hoax. Why would a popular student make herself disappear Her motive remains a mystery, but perhaps it had something to do with the search parties and the news bulletins that surrounded her.

Sympathy is a powerful sentiment that can connect complete strangers. But if it’s used to manipulate, the backlash can be much more intense.

In February, a Waterbury, Connecticut, man was arrested as a result of exploiting sympathy. Edward Valentin told reporters that he had received word that his wife, serving in Iraq, had been killed in an explosion. Police said Valentin admitted the fabrication, reasoning that if people felt sorry for him maybe the military would send his wife home. Evidence, however, points elsewhere.

In its extreme form, such a craving shows up in mental disorders, where sufferers may seek attention by causing themselves harm. But even when it comes with no diagnosis, a deep craving to be noticed can have a wide impact.

For these individuals, victim hood represents a "pure state of guilt-free entitlement," said psychologist Richard Levak, of Del Mar, California. "They go from being utterly deprived to being utterly indulged. In today’s world ... people have become more depressed and disconnected from each other. So you get people who crave affection and attention and approval. They don’t know how to ask for it and they don’t know how to get it. That leaves them vulnerable. " Levak said.

According to the first paragraph, some people ().

A. do not like to be in the spotlight

B. like the dark side of society

C. prefer the beauty of plants to people

D. avoid the media but enjoy parties

问答题 简答题