问题 选择题

当电阻两端加上某一稳定电压时,通过该电阻的电荷量为0.3C,消耗的电能为0.9J.为在相同时间内使0.6C的电荷量通过该电阻,在其两端需加的电压和消耗的电能分别是(  )

A.3V,1.8J

B.3V,3.6J

C.6V,1.8J

D.6V,3.6J

答案

因为电阻丝在通过0.3C的电量时,消耗的电能是0.9J,所以此时电压为:

U′=

W′
Q′
=
0.9
0.3
=3V

当在相同的时间内通过电阻丝的电量是0.6C时,根据I=

Q
t
可知,I=2I′,

根据U=IR可知,电阻不变,此时电阻丝两端电压:U=2U′=6V,

电阻丝在这段时间内消耗的电能:

W=UQ=6V×0.6C=3.6J.

故选D.

单项选择题

Passage Three

A rapid means of long-distance transportation became a necessity for the United States as settlement (新拓居地) spread ever farther westward. The early trains were impractical curiosities, and for a long time the railroad companies met with troublesome mechanical problems. The most serious ones were the construction of rails able to bear the load, and the development of a safe, effective stopping system. Once these were solved, the railroad was established as the best means of land transportation. By 1860 there were thousands of miles of railroads crossing the eastern mountain ranges and reaching westward to the Mississippi. There were also regional southern and western lines.
The high point in railroad building came with the construction of the first transcontinental system. In 1862 Congress authorized two western railroad companies to build lines from Nebraska westward and from California eastward to a meeting point, so as to complete a transcontinental crossing linking the Atlantic seaboard with the Pacific. The Government helped the railroads generously with money and land. Actual work on this project began four years later. The Central Pacific Company, starting from California, used Chinese labor, while the Union Pacific employed crews of Irish laborers. The two groups worked at remarkable speed, each trying to cover a greater distance than the other. In 1869 they met at a place called Promontory in what is now the state of Utah. Many visitors came there for the great occasion. There were joys all over the country, with parades and the ringing of church bells to honor the great achievement.
The railroad was very important in encouraging westward movement. It also helped build up industry and farming by moving raw materials and by distributing products rapidly to distant markets. In linking towns and people to one another it helped unify the United States.

The building of the first transcontinental system ______.

A.relieved the burden of overall railroad system

B.encouraged people to rush for gold in the west

C.attracted many visitors to the construction sites

D.brought about a rapid growth of industry and farming in the west

单项选择题