问题 问答题

如图所示的装置探究“导体产生的热量与电阻大小的关系”.两瓶煤油中都浸泡着一段金属丝,烧瓶A中的金属丝是铜丝,电阻比较小,烧瓶B中的金属丝是镍铬合金丝,电阻比较大.

(1)这两个烧瓶中所盛煤油的质量应该______;

(2)实验中不用水而用煤油的原因是:______;

(3)电路采用这种连接方式的目的是______;

(4)合上开关后,经过一段时间,两电阻丝产生热量的多少是通过______反映出来的;

(5)实验中,发现B烧瓶中温度计的示数升高的快.这表明:在电流和通电时间相同的情况下,导体的电阻越______,产生的热量越多.

答案

(1)要能准确地显示热量的变化,则应控制质量相等相等;

(2)因煤油比水具有较小的比热容,故用煤油比用水更容易看出温度的变化;

(3)两电阻丝串联,因串联电路中电流相等,故此接法是为了控制电流相等,

(4)电阻产生的热量被煤油吸收后,煤油的温度会升高,故从温度计的示数变化可知两电阻丝产生的热量的多少;

(5)B烧瓶内温度计示数升高的快,说明B中电阻丝产生的热量多,因两瓶中通过电阻的电流相等,故说明导体电阻越大,产生的热量越多.

故答案为:(1)相等;(2)煤油比水的比热容大;(3)控制电流相等;(4)温度计的示数变化;(5)大.

单项选择题
单项选择题

The percentage of immigrants (including those unlawfully present) in the United States has been creeping upward for years. At 12.6 percent, it is now higher than at any point since the mid 1920s. We are not about to go back to the days when Congress openly worried about inferior races polluting America’s bloodstream. But once again we are wondering whether we have too many of the wrong sort of newcomers. Their loudest cites argue that the new wave of immigrants cannot, and indeed do not want to, fit in as previous generations did.

We now know that these racist views were wrong. In time, Italians, Romanians and members of other so called inferior races became exemplary Americans and contributed greatly, in ways too numerous to detail, to the building of this magnificent nation. There is no reason why these new immigrants should not have the same success.

Although children of Mexican immigrants do better, in terms of educational and professional attainment, than their parents, UCLA sociologist Edward Telles has found that the gains don’t continue. Indeed, the fourth generation is marginally worse off than the third. James Jackson, of the University of Michigan, has found a similar rend among black Caribbean immigrants, Telles fears that Mexican Americans may be fated to follow in the footsteps of American blacks—that large parts of the community may become mired in a seemingly state of poverty and underachievement. Like African Americans, Mexican Americans are increasingly relegated to (降入) segregated, substandard schools, and their dropout rate is the highest for any ethnic group in the country.

We have learned much about the foolish idea of excluding people on the presumption of the ethnic/racial inferiority. But what we have not yet learned is how to make the process of Americanization work for all. I am not talking about requiring people to learn English or to adopt American ways; those things happen pretty much on their own, but as arguments about immigration hear up the campaign trail, we also ought to ask some broader question about assimilation, about how to ensure that people, once outsiders, don’t forever remain marginalized within these shores.

That is a much larger question than what should happen with undocumented workers, or how best to secure the border, and it is one that affects not only newcomers but groups that have been here for generations. It will have more impact on our future than where we decide to set the admissions bar for the latest ware of would be Americans. And it would be nice if we finally got the answer right.

What should be done to help the new immigrants()

A.Rid them of their inferiority complex.

B.Urge them to adopt American customs.

C.Prevent them from being marginalized.

D.Teach them standard American English.