题干

图甲是一种常见的电热水袋,图乙是它的结构示意图.为了使用安全,电热水袋在用电加热到一定温度时温控开关S会自动切断电路,与此同时专用插头上的红色指示灯L会熄灭起提示作用.

(1)电热水袋里面一般用水作储能物质,除了水容易获得、成本低廉的原因外,还有一个重要原因是____ .
(2)温控开关s的内部结构如图丙所示:双金属片由两层不同金属粘合而成,受热时二者膨胀的快慢不同,金属层膨胀,达到一定温度时,双金属片向上拱起,从而切断电路.如果温控开关失灵,水温超过预定温度而不切断电源,热水袋会因内部压强过高而爆炸.为了更加安全,有的电热水器里使用双重温控开关保护,也就是把两个温控开关____ 起来使用.(填“串联”或“并联)
(3)某电热水袋的性能指标如表,当热水袋中水原来的温度是10℃时,在额定电压下加热10min指示灯就熄灭了, 该电热水袋的效率____ .[c水=4.2×103J/(kg•℃),  Q=cm△t]

额定电压额定加热功率指示灯功率袋内充水自动断电温度
220V700W≤0.2W1L80℃


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答案(点此获取答案解析)

水的比热大,串联,70%

同类题3

根据短文内容,从短文后面的选项中选出能填入空白处的最佳选项。选项中有两项为多余选项。

    What should you think about in trying to find your career(职业)? You are probably better at some school subjects than others. ____ A boy who is good at mathematics can use that in an engineering career. ____ So it is important to do well at school. On the other hand, you may not have any specially strong or weak subjects but your records show a general satisfactory standard. ____ Knowledge of history is not required for most jobs but if history is one of your good subjects you will have learned to remember facts and details. This is an ability that can be useful in many jobs.

    ____ If nothing else, you may have learned how to get to work on time, to follow instructions and to get on with older workers. Just as important, you may become interested in a particular industry or career you see from the inside in a part-time job.

    Facing your weak points is also part of knowing yourself. ____ Your school record, for instance, may not be too good, yet it is an important part of your background. You should not be apologetic about it but instead recognize that you will have a chance of a fresh start at work.

A. It is better to face any weaknesses than to pretend they do not exist.

B. A girl who spells well and likes English may be good at office work.

C. He may do well in his future work.

D. Although not all subjects can be used directly in a job, they may have indirect value.

E. Your school must have taught you the skills.

F. These may show strengths (优势) that you can use in your work.

G. If you have had a part-time job on Saturday or in the summer, think what you gained from it.