问题 计算题

如图所示的电路,灯泡L标有“12V  4W”字样,滑动变阻器最大电阻为36 Ω,当开关S闭合,滑动变阻器的滑片P移到最右端时,小灯泡正常发光。求:

①灯泡电阻;

②电源电压;

③当开关S断开,滑片P移到变阻器的最左端时,灯泡消耗的功率是多少?

答案

解:①

②当开关S闭合,滑动变阻器的滑片P移到最右端时,灯泡和滑动变阻器并联;又因为小灯泡正常发光,并且小灯泡的额定电压为12V,所以电源电压U=UL=12V;

③当开关S断开,滑片P移到变阻器的最左端时,小灯泡与滑动变阻器串联,即电路中的电流为:

填空题
单项选择题

Few beyond California’ s technology crowd recognise the name Larry Sonsini; none within its circle could fail to. For four decades he has been lawyer, adviser and friend to many prominent companies and investors. Some consider him the most powerful person in Silicon Valley. Companies beg for his law firm to represent them. The 65-year-old chairman of Wilson Sonsini Goodrich & Rosati (WSG&R) has suddenly been thrust into the spotlight: first, for counselling many of the technology firms now under scrutiny for backdating stock options (and in some cases, serving on their boards); and more recently, as outside counsel to Hewlett-Packard (HP), for initially defending the board’s dubious investigative practices.

WSG&R boasts 600 lawyers and represents around half of Silicon Valley’s public companies, including Apple Sun Microsystems and Google. Last year it ranked first in private-equity and venture-capital deals, with nearly twice as many as its closest rival. Over the past five years WSG&R has worked on over 1 000 mergers and acquisitions, collectively worth over $ 260 billion.

The recent troubles cast a shadow over WSG&R’s reputation. Although Mr. Sonsini is not accused of wrongdoing himself, many of his firm’s clients are on the ropes. Former executives at Brocade Communications suffered criminal charges in July, Mr. Sonsini Served on Brocade’s board until last year and his firm was its outside counsel. He also was on the boards of Pixar, Echelon, Lattice Semiconductor, LSI Logic and Novell all firms at which the issuing of stock options is being called into question.

WSG&R dismisses the idea that Mr. Sonsini faced a conflict of interest by acting as both director and legal adviser to so many firms and says he did not advise HP in its investigation of board members. Mr. Sonsini initially said it was "well done and within legal limits". It now seems it was neither.

The statistics in the text indicate ()

A. the fame of WSG&R

B. the notoriety of Larry Sonsini

C. the boom of WSG&R

D. the obligation of Hewlett-Packard