问题 选择题

美国《科学》杂志曾发表“新超导体将中国物理学家推到最前沿”的评述.这表明,在新超导体领域,我国取得了令人瞩目的成就.假如人们已经研制出常温下的超导体,则你可以用它制作(  )

A.远距离输电导线

B.白炽灯泡的灯丝

C.电炉的电阻丝

D.家用保险丝

答案

A、根据焦耳定律Q=I2Rt,可知,远距离输电,当电阻为零时,可使导线损耗为零,便可提高传输效率,符合题意.

B、灯丝必须在白炽状态下才能正常发光,电阻为零无法将电能转化为内能,无法放热,不符合题意.

C、电炉丝需要将电能转化为内能,电阻为零无法将电能转化为内能,不符合题意.

D、保险丝是利用电流的热效应,当电流过大时,自动熔断来保护电路的.电阻为零无法将电能转化为内能,无法熔断,不符合题意.

故选A.

单项选择题
单项选择题 案例分析题

Questions 21 to 25 are based on the following passage.

Lead deposits, which accumulated in soil and snow during the 1960’s and 70’s, were primarily the result of leaded gasoline emissions originating in the United States. In the twenty years that the Clean Air Act has mandated unleaded gas use in the United States, the lead accumulation worldwide has decreased significantly.

A study published recently in the journal Nature shows that air-borne leaded gas emissions from the United States were the leading contributor to the high concentration of lead in the snow in Greenland. The new study is a result of the continued research led by Dr. Charles Boutron, an expert on the impact of heavy metals on the environment at the National Center for Scientific Research in France. A study by Dr. Boutron published in 1991 showed that lead levels in arctic (北极的) snow were declining.

In his new study, Dr. Boutron found the ratios of the different forms of lead in the leaded gasoline used in the United States were different from the ratios of European, Asian and Canadian gasolines and thus enabled scientists to differentiate (区分) the lead sources. The dominant lead ratio found in Greenland snow matched that found in gasoline from the United States.

In a study published in the journal Ambio, scientists found that lead levels in soil in the Northeastern United States had decreased markedly since the introduction of unleaded gasoline.

Many scientists had believed that the lead would stay in soil and snow for a longer period.

The authors of the Ambio study examined samples of the upper layers of soil taken from the same sites of 30 forest floors in New England, New York and Pennsylvania in 1980 and in 1990. The forest environment processed and redistributed the lead faster than the scientists had expected.

Scientists say both studies demonstrate that certain parts of the ecosystem (生态系统) respond rapidly to reductions in atmospheric pollution, but that these findings should not be used as a license to pollute.

The study published in the journal Nature indicates that ()

A.the Clean Air Act has not produced the desired results

B.lead deposits in arctic snow are on the increase

C.lead will stay in soil and snow longer than expected

D.the US is the major source of lead pollution in arctic snow