问题 问答题

如图所示,在正点电荷Q的一条电场线上的A处,放一个电荷量大小为4.0×10-6C的正点电荷q1,q1受到的电场力F1=1.2×10-2N.求:

(1)A点处的电场强度EA的大小和方向如何?

(2)如果在A处换上另一个电荷量大小为3.0×10-6C的负点电荷q2,它所受到的电场力F2的大小和方向如何?

(3)若再A处不放电荷,则该处的电场强度多大?

答案

(1)由电场强度的定义式可得

A点处电场强度大小:EA=

F1
q1
=
1.2×10-2
4.0×10-6
=3×105N/C

电场强度的方向:从Q指向A点.

(2)负点电荷q2受到的电场力的大小F2=q2EA=3.0×10-6×3.0×105=0.9N

其方向:指向正点电荷Q向左

(3)若在A处不放电荷,该处的电场强度不变,仍为3×105N/C,

答:(1)A点处的电场强度的大小为3×105N/C,方向为从Q指向A点.

(2)负点电荷q2受到的电场力F2的大小为0.9N,方向为指向正点电荷Q向左.

(3)若再A处不放电荷,则该处的电场强度仍为3×105N/C.

判断题
单项选择题

"WHAT’S the difference between God and Larry Ellison" asks an old software industry joke. Answer: God doesn’t think he’s Larry Ellison. The boss of Oracle is hardly alone among corporate chiefs in having a reputation for being rather keen on himself. Indeed, until the bubble burst and the public turned nasty at the start of the decade, the cult of the celebrity chief executive seemed to demand bossly narcissism, as evidence that a firm was being led by an all-conquering hero.

Narcissus met a nasty end, of course. And in recent years, boss-worship has come to be seen as bad for business. In his management bestseller, "Good to Great", Jim Collins argued that the truly successful bosses were not the serf-proclaimed stars who adorn the covers of Forbes and Fortune, but instead self-effacing, thoughtful, monkish sorts who lead by inspiring example.

A statistical answer may be at hand. For the first time, a new study, "It’s All About Me", to be presented next week at the annual gathering of the American Academy of Management, offers a systematic, empirical analysis of what effect narcissistic bosses have on the firms they run. The authors, Arijit Chatterjee and Donald Hambrick, of Pennsylvania State University, examined narcissism in the upper levels of 105 firms in the computer and software industries.

To do this, they had to solve a practical problem: studies of narcissism have hitherto relied on surveying individuals personally, something for which few chief executives are likely to have time or inclination. So the authors devised an index of narcissism using six publicly available indicators obtainable without the co-operation of the boss. These are: the prominence of the boss’s photo in the annual report; his prominence in company press releases; the length of his "Who’s Who" entry; the frequency of his use of the first person singular in interviews; and the ratios of his cash and non-cash compensation to those of the firm’s second-highest paid executive.

Narcissism naturally drives people to seek positions of power and influence, and because great self-esteem helps your professional advance, say the authors, chief executives will tend on average to be more narcissistic than the general population. How does that affect a firm Messrs Chatterjee and Hambrick found that highly narcissistic bosses tended to make bigger changes in the use of important resources, such as research and development, or in spending and leverage; they carried out more and bigger mergers and acquisitions ; and their results were both more extreme (more big wins or big losses) and more transient than those of firms run by their humbler peers. For shareholders, that could be good or bad.

Although (oddly) the authors are keeping their narcissism ranking secret, they have revealed that Mr Ellison did not come top. Alas for him, that may be because the study limited itself to people who became the boss after 1991--well after he took the helm. In every respect Mr Ellison seems to be the classic narcissistic boss, claims Mr Chatterjee. There is life in the old joke yet.

We can infer from the passage that()

A. the results of the new study has already been publicized

B. the researchers think Mr. Ellison is more classic than narcissistic

C. the joke about Mr. Ellison is actually adapted from real life

D. the ranking might be different if the survey focused on an earlier period