问题 选择题

如图所示的电路中,输入电压U恒为12V,灯泡L上标有“6V、12W”字样,电动机线圈的电阻RM=0.50Ω.若灯泡恰能正常发光,下列说法正确的是(  )

A.电动机的输入功率为12W

B.电动机的输出功率为12W

C.电动机的热功率为12W

D.整个电路消耗的电功率为22W

答案

A、电动机两端的电压U1=U-UL=12-6V=6V,整个电路中的电流I=

PL
UL
=2A,所以电动机的输入功率P=U1I=6×2W=12W.故A正确.

B、C、电动机的热功率P=I2RM=4×0.5W=2W,则电动机的输出功率P2=P-I2RM=12-2W=10W.故B错误,C错误.

D、整个电路消耗的功率P=UI=12×2W=24W.故D错误.

故选:A.

阅读理解

阅读理解。

     阅读下面的短文,并根据短文后的要求答题(请注意问题后的字数要求).

     A mobile phone service which makes your handset scream when it's been stolen has been started,

with its makers claiming it could put an end to mobile theft altogether.

     The Remote XT system uses software to link customers' mobile phones directly to a secure remote

server, which stores all their data from phone numbers to text messages and e-mails. If the owner's phone

is lost or stolen, they can dial a 24-hour call centre and have it registered. The handset is then disabled,

and cannot even be used if a new SIM card is put in. At the same time, the system sets off an alarm

sounding like a high-pitched(尖声的) scream, which can only be stopped by removing the battery.

     Existing data is also wiped off the phone but, because the information has been stored centrally,         

as soon as the victim gets a news phone, the system designers said.

     "By making mobiles unusable to anyone but the rightful owner the phones become worthless and we

will see the market for stolen handsets stopped once and for all," said Mark Whiteman, managing

director of Remote XT. For the moment the system is aimed at business customers and comes with a

fee of 9.99 pounds per month, possibly available to the majority of average users within two years as

mobile technology advances.

      According to the latest UK government statistics, mobile phone theft has risen 190 percent in recent

years, with one third of all UK robberies now solely involving mobile phones.

1. What is the best title for the passage? (Please answer within 10 words.)

2. Which sentence in the passage can be replaced by the following one?

With a phone lost or stolen, the phone's user can call a service centre at any time, having his/ her case

recorded.

3. Please fill in the blank in Paragraph 3 with proper words or phrases to complete the sentence. (Please

answer within 10 words.)

4. Do you believe the security system can put an end to phone theft? Try to give your reasons. (Please

answer within 30 words.)

____________________________________________________________________________

5. Translate the underlined sentence in Paragraph 4 into Chinese.

单项选择题