问题 探究题

小明想测一只电阻的阻值,但身边只有一只10Ω 的电阻、一个电流表、电源、开关和导线,你能利用这些器材替他想出一个办法吗?

答案

如图所示,将待测电阻Rx与10Ω的电阻R1并联,用电流表分别测出Rx的电流Ιx和R1的电流,根据并联电路电压相等.ΙxRx1R2,所以Rx=10Ι1xΩ.

 

单项选择题

In 1998 consumers could purchase virtually anything over the Internet. Books, compact discs, and even stocks were (1) from World Wide Websites that seemed to (2) almost daily a few years earlier, some people had predicted that consuners accustomed to shopping in stores would be (3) to buy things that they could not see or touch (4) . For a growing number of time-starved consumers, however, shopping from their home computer was proving to be a convenient (5) to driving to the store.

A research estimated that in 1998 US consumers could purchase $ 7.3 billion of goods over the Internet, double the 1997 total. Finding a bargain was getting easier, (6) the rise of online auctions and Websites that did comparison shopping on the Internet for the best (7) .

For all the consumer interest, (8) in eyberspaee was still a largely (9) business, however. Internet pioneer Amazon. eom, which began selling books in 1995 and later (10) into recorded music and videos, posted (11) of $ 153.7 million in the third quarter, up from $ 37.9 million in the same period of 1997. Overall, (12) , the company’ s loss widened to $ 45.2 million from $9.6 million, and analysts did not expect the company to turn a profit (13) 2001. (14) the great loss, Amazon. tom had a stock market value of many billions, reflecting investors’ (15) about the future of the industry.

Internet retailing appealed (16) investors because it provided an efficient means for reaching millions of consumers without having the cost of operating (17) stores with their armies of salespeople. Selling online carried its own risks, however, (18) so many companies competing tor consumers’ attention, price competition was (19) and profit (20) thin or nonexistent.

20()

A.benefits

B.margins

C.advantages

D.gains

单项选择题