试题与答案

如图甲所示是某人设计的一种振动发电装置,它的结构是一个套在辐向形永久磁铁槽中的半

题型:问答题

题目:

如图甲所示是某人设计的一种振动发电装置,它的结构是一个套在辐向形永久磁铁槽中的半径为r=0.1m、匝数n=20的线圈,磁场的磁感线均沿半径方向均匀分布(其右视图如图乙所示).在线圈所在位置磁感应强度B的大小均为0.2T,线圈的电阻为2Ω,它的引出线接有8Ω的小电珠L.外力推动线圈框架的P端,使线圈沿轴线做往复运动,便有电流通过电珠.当线圈向右的位移x随时间t变化的规律如图丙所示时(x取向右为正),求:

(1)线圈运动时产生的感应电动势E的大小;

(2)线圈运动时产生的感应电流I的大小,并在图丁中画出感应电流随时间变化的图象(在图甲中取电流由C向上流过电珠L到D为正);

(3)每一次推动线圈运动过程中作用力F的大小;

(4)该发电机的输出功率P(摩擦等损耗不计);

(5)某同学说:“该线圈在运动过程中,磁感线始终与线圈平面平行,线圈中的磁通量始终为零,磁通量保持不变,因此线圈中应该没有感应电流产生,但实际却产生了电流,如何解释这个问题呢?”对这个问题说说你的看法.

答案:

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Washington, DC has traditionally been an unbalanced city when it comes to the life of the mind. It has great national monuments, from the Smithsonian museums to the Library of Congress. But day-to-day cultural life can be thin. It attracts some of the country’s best brains. But far too much of the city’s intellectual life is devoted to the minutiae of the political process. Dinner table conversation can all too easily turn to budget reconciliation or social security.

This is changing. On October 1st the Shakespeare Theatre Company opened a 775-seat new theatre in the heart of downtown. Sidney Harman hall not only provides a new stage for a theatre company that has hitherto had to make do with the 450-seat Lansburgh Theatre around the corner. It will also provide a platform for many smaller arts companies.

The fact that so many of these outfits are queuing up to perform is testimony to Washington’s cultural vitality. The recently-expanded Kennedy Centre is by some measures the busiest performing arts complex. But it still has a growing number of arts groups which are desperate for mid-sized space down- town. Michael Kahn, the theatre company’s artistic director, jokes that, despite Washington’s aversion (厌恶) to keeping secrets, it has made a pretty good job of keeping quiet about its artistic life. The Harman Centre should act as a whistle blower.

Washington still bows the knee to New York and Chicago when it comes to culture. But it has a good claim to be America’s intellectual capital. It has the greatest collection of think-tanks on the planet, and it regularly sucks in a giant share of the country’s best brains. Washington is second only to San Francisco for the proportion of residents twenty-five years and older with a bachelor’s degree or higher.

Washington’s intellectual life has been supercharged during the Bush years, despite the Decider’s aversion to ideas. September 11th, 2001, put questions of global strategy at the center of the national debate. Most of America’s intellectual centers are firmly in the grip of the left-liberal establishment. For all their talk of "diversity" American universities are allergic to a diversity of ideas. Washington is one of the few cities where conservatives regularly do battle with liberals. It is also the center of a fierce debate about the future direction of conservatism.

The danger for Washington is that this intellectual and cultural renaissance will leave the majority of the citizens untouched. The capital remains a city deeply divided between over-educated white itinerants and under- educated black locals. Still, the new Shakespeare theatre is part of job-generating downtown revival. Twenty years ago downtown was a desert of dilapidated(破旧的) buildings and bag people. Today it is bustling with life. If Washington is struggling to fix the world, at least it is making a reasonable job of fixing itself.

By mentioning the 9·11 terrorist attack in Paragraph 5, the author intends to ()

A. discuss the changes of Washington’s cultural life in Bush’s administration

B.indicate that Washington’s intellectual life is more developed than elsewhere

C. highlight the question of American global strategy in the national debate

D.draw a Comparison between American universities and Washington

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