问题 选择题

压敏电阻的阻值随所受压力的增大而减小。某实验小组在升降机水平地面上利用压敏电阻设计了判断升降机运动状态的装置。其工作原理图如图甲所示,将压敏电阻、定值电阻R、电流显示器、电源E连成电路,在压敏电阻上放置一个绝缘重物。0~t1时间内升降机停在某一楼层处,t1时刻升降机开始运动,从电流显示器中得到电路中电流i随时间t变化情况如图乙所示。则下列判断正确的是(   )

时间内绝缘重物处于失重状态,时间内绝缘重物处于超重状态

时间内绝缘重物处于超重状态,时间内绝缘重物处于失重状态

③升降机开始时可能停在10楼,从时刻开始,经向下加速、匀速、减速,最后停在1楼

④升降机开始时可能停在1楼,从时刻开始,经向上加速、匀速、减速,最后停在10楼

A.①③

B.①④

C.②③

D.②④

答案

答案:A

压敏电阻的阻值随所受压力的增大而减小,当电梯向下加速(或向上减速)时,重物发生超重现象,对压敏电阻压力变大,其电阻减小,电流将增大;当电梯向上加速(或向下减速)时,重物发生失重现象,对压敏电阻压力变小,其电阻增大,电流将减小。由此可判断时间内绝缘重物处于失重状态,时间内绝缘重物处于超重状态,选项③中升降机的运动情况能够满足重物在相应时间段内的超失重状态,故①③对,本题应选A。

单项选择题
单项选择题

It was two years ago today that the hunting ban came into force, supposedly ending centuries of tradition. However, the law has been an unmitigated failure—not that either side is shouting about it.

It was a nightmare vision that struck fear and loathing into the hearts of millions. When the hunting ban became law, it was said, 16,000 people would lose their jobs, thousands of hounds would be put down, rotting carcasses would litter the countryside, hedgerows would disappear, riders would face on-the-spot fines, law-abiding people from doctors to barristers would be dragged from their horses and carted off to prison, while dog owners would be prosecuted if their mutt caught a rabbit.

These were just some of the claims as desperate countryside campaigners battled to save their sport in the lead—up to the hunting ban, which Labour rammed into law using the Parliament Act on November 18, 2004.

For many, the fears were real. Others exaggerated as they fought an increasingly aggressive anti-hunting lobby which had rejected acres of independent evidence affirming that hunting is the most humane way of killing foxes. In the battle to "fight prejudice, fight the ban", every emotive argument was deployed.

For its part, the anti-hunting brigade extravagantly claimed that the ban would put an end to the rich parading in red jackets. A senior Labour MP, Peter Bradley, admitted in this newspaper that it was, as many suspected, about "class war" . He lost his seat shortly afterwards. But people in red coats did not disappear.

In fact, none of the forecasts came true. What did happen was something nobody had predicted, the spectacular revival and growth of hunting with hounds. In short, the hunting ban has been a failure.

Today, on the second anniversary of the ban’s coming into force on February 18, 2005, new figures show that participation in the sport has never been higher. It is so cheerful that two new packs have been formed, something that has not happened for centuries.

They include the seductively named Private Pack, set up by the financier Roddy Fleming in Gloucestershire. It operates on an invitation-only basis, a sort of hunting private members’club. This can only mean one thing: like it or not, hunting is cool. Young people are taking it up, enticed by the element of rebellion and the mystique of what actually happens as hunts attempt to keep within the law.

The anti-hunting lobby held that ().

A. fox-hunting was an expression of prejudice

B. the countryside campaigners were reasonable

C. the theory of humane killing did not hold water

D. the hunters exaggerated the dreadful scene of hunting