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问题 计算题

如图家用电器的电路图，R1是“220V 1100W”的电热丝，L是指示灯，R2是0﹣500Ω的变阻器，S是双联转换开关，电源电压不变．（不计温度对电阻的影响）（ 双联转换开关指同时接通两个触点）

（1）当S放置1、2位置时，R1正常工作，若L电阻为1210Ω，求整个电路消耗的电功率．

（2）当s放置3、4位置时，调节R2，使整个电路消耗功率为110W，求此时R2阻值．

答案

解：（1）由电路图知，开关置于1.2位置时，R1正常工作

由R1铭牌“220V 1100W”知：

此时电源电压等于R1的额定电压U=U1=220V

R1的功率等于其额定功率P1=1100W

指示灯L的功率

PL===40W

整个电路消耗的电功率

P=P1+PL=1100W+40W=1140W

（2）开关放置在3.4位置时，电路总功率P'=110W，则电路总电阻

R===440Ω

电阻R1的阻值

R1==44Ω

滑动变阻器的阻值

R2=R﹣R1=440Ω﹣44Ω=396Ω

完形填空

阅读下面短文，根据以下提示：1)汉语提示，2)首字母提示，3)语境提示，在每个空格内填入一个适当的英语单词，所填单词要求意义准确，拼写正确，并将该词完整地写在答题卡中相应的横线上。

A recent study suggests that students who bring water into exams may improve their grades by 10 percent．

Scientists then小题1:____(比较) their exam results with their normal schoolwork grades．They found that all those 小题2:______had brought drinks with them got better grades．

Scientists also considered the students 'schoolwork and小题3:_____(预计)their grades．This was to make sure that the reason was not simply that smarter students were more小题4:________(有可能)to bring drinks with them．

小题5:______is unclear why drinking water improves exam results．But scientists say having enough water in our小题6:b      and not feeling thirsty could have a helpful effect 小题7:________our brains．Drinking water may also cut小题8:d_____ on anxiety ,which affects exam performances．

So next time，小题9:w    you are going to have a big exam，try bringing a bottle of water with you．Who knows—it may help you小题10:p     the exam!
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单项选择题

温 * * * * 在报告中首次提出“老百姓活得有尊严！”。这再次说明国家机构坚持（）。

A.对人民负责的原则

B.民主集中制的原则

C.依法治国的原则

D.法律面前人人平等的原则
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