问题 选择题

如图2—2所示电路中,电源电动势E,内阻r均不变,当外电阻R变化时,下列说法中正确的是

A.因为U = IR,所以R增大时,路端电压也增大

B.因为U = E-Ir,所以电流I增大时,路端电压减小

C.因为U = IR,当电阻R增大时,电流I减小,所以路端电压不变

D.因为U = Ir,所以当电流I增大时,路端电压增大

答案

答案:B

当R增大时,I减小,所以不可以利用U = IR,判断路端电压的变化,故AC错误

当外电阻R变化时,因为U = E-Ir,所以电流I增大时,路端电压减小,故B正确

内电压U = Ir,当电流I增大时,内电压增大,故D错误

故选B

阅读理解

BEIJING - By the end of 2011 China-made supercomputers will say goodbye to foreign microchips(微芯片) and start using their own "Chinese core(核心)", according to one of the country's leading scientists, Hu Weiwu.

Hu told reporters on Saturday that the "Dawning 6000" supercomputer, developed by the Institute of Computing Technology of CAS and the Dawning Information Industry Company (DIIC), will adopt Loongson microchips for the first time as its core parts. It will have a computing speed of more than 1,000 trillion operations a second.

Making supercomputers with Chinese microchips is one of the nation's major science and technology projects. Three organizations - the Institute of Computing Technology of CAS, Jiangnan Institute of Computing Technology and the National University of Defense Technology (NUDT) - have their own supercomputer projects.

According to their schedules, all three institutions will need to meet the target of using domestically(国内的) developed microchips by the end of this year. Hu said the new supercomputer will use fewer than 10,000 Loongson microchips, and will also be more energy-efficient.

Tianhe-1A, developed by NUDT in Hunan's provincial capital Changsha, is the fastest supercomputer in the world. However, Tianhe-1A largely runs on 14,336 CPUs made by Intel, and 7,186 GPUs (processing units) from Nvidia, two US chip-makers.

Hu said there will be difficulties ahead as there is little affiliated equipment specially developed for these supercomputers. "We have enough supercomputers in China but still can't make full use of them," He said.

Hu added that although the China-made CPUs have improved since they were first produced in 2002, they have a long way to go to compete with US chip-makers such as Intel.

小题1:What’s the best title for this passage?

A.The Arrival of Chinese Supercomputers

B.Homemade CPUs with a Long Way to Go

C.The Supercomputers of Three Organizations in China

D.Homemade CPUs on the Way for Local Supercomputers小题2:What will raise the speed to more than 1,000 trillion operations a second.?

A.Dawning 6000

B.Loongson microchips

C.DIIC

D.Tianhe-1A小题3:What do we know about Tianhe-1A?

A. Not all the parts of Tianhe-1A are made by China.

B. Tianhe-1A is developed by CAS and DIIC.

C. Tianhe-1A will use fewer than 10,000 Loongson microchips.

D. NUDT has produced a most powerful supercomputer in China.

小题4:The underlined word “affiliated” can be replaced by_______.

A.cheap

B.suitable

C.expensive

D.modern

单项选择题