问题 计算题

一家用电热水器的铭牌如下表所示,已知C=4.2×103J/(kg·℃),根据铭牌所提供的信息,回答下列问题:

(1)为安全起见,该电热水器应使用的插座应选用如图所示的哪一种?

(2)该电热水器正常工作时电热丝的电阻为多大?

(3)将该电热水器加满水加热使水温由20℃升高到60℃,水需要吸收多少热量?

(4)若电热水器正常工作时电热所产生热量的80%被水吸收,则第(3)问中的加热过程需要多少时间?

答案

解:(1)乙

(2)I=P/U=2000W/220V=9.09A

      R=U/I=220V/9.09A=24.2Ω

(3)m=ρV=1×103kg/m3×12×10-3 m3=12kg

      Q=cm△t=4.2×103J/(kg·℃)×12kg×(60℃-20℃)=2.016×106J

(4)Q=Q/η=2.016×106J/80%=2.52×106J

      t=W/P=Q/P=2.52×106J/2000W=1260s=21min

选择题
阅读理解

Clearly if we are to participate in the society in which we live, we must communicate with other people. A great deal of communicating is performed on a person-to-person basis by the simple means of speech. If we travel in buses, buy things in shops, or eat in restaurants, we are likely to have conversations where we give information or opinions, receive news or comment, and very likely to have our views challenged by other members of society.

Face to face contact is by no means the only form of communication and during the last two hundred years the art of mass communication has become one of the dominating factors of contemporary society. Two things, above others, have caused the enormous growth of the communication industry. Firstly, inventiveness has led to advanced imprinting, telecommunications photography, radio and television. Secondly, speed has revolutionized the transmission (传输) and reception of communications so that local news often takes a back seat to national news, which itself is often almost eclipsed( 侵蚀) by international news.

No longer is the possession of information confined to(只限于) a privileged minority. In the last century the wealthy man with his own library was indeed fortunate, but today there are public libraries. For years ago people used to flock to the cinema, but now far more people sit at home and turn on the TV to watch a programme that is being channeled into millions of homes.

Communication is no longer merely concerned with the transmission of information. The modem communication industry influences the way people live in society and broadens their horizons by allowing access to information, education and entertainment. The printing, broadcasting and advertising industries are all involved with informing, educating and entertaining.

Although a great deal of the material communicated by the mass media is very valuable to the individual and to the society of which he is part, the vast modem network of communications is open to abuse(滥用). However, the mass media are with us for better, for worse, and there is no turning back.

小题1:In the first paragraph the writer emphasizes the       of face-to-face contact in social setting.

A.nature

B.limitation

C.creativity

D.usefulness小题2:It is implied in the passage that         .

A.local news used to be the only source of information

B.local news still takes a significant place

C.national news is becoming more popular

D.international news is the fastest transmitted news小题3:Which of the following statements is NOT true?       

A.Possessing information used to be a privilege.

B.Public libraries have replaced the private completely.

C.Communication means more than transmission.

D.Information influences ways of life and thinking.小题4:From the last paragraph we can infer that the writer is       .

A.indifferent to the harmful influence of the mass media

B.happy about the flexible changes in the mass media

C.pessimistic about the future of the mass media

D.concerned about the wrong use of the mass media