问题 计算题

如图是小明自制电子秤的原理示意图.托盘、轻弹簧上端和金属滑片P固定一起(弹簧的电阻不计).

电路设计:要使电子秤能正常工作,必须把点“2”与点“3”连接起来.

(1)刻度调试:

①调零.在托盘中无物体时,使金属滑片P处于Rl最上端.此时电压表的示数为零.

②标度.每次向托盘中增加100g的砝码,在电压表指针所指位置的刻度盘上标出相应的质量值.当将1kg的物体放在托盘中.金属滑片P刚好指在距Rl上端l/3处(如图),请计算回答“lkg”应标在电压表多少伏的位置上?(电阻R0=5Ω,电阻R1=15Ω,电源电压U=3.0V,电压表的量程为0~3.0V)

(2)继续改进:小明在标示电子秤刻度时,发现电子秤的刻度与电压表的刻度有不同特点.请说出不同之处 _________ .于是,他又开始了新的研究.

答案

(1)距Rl上端l/3处的电阻R=R1=×15Ω=5 Ω,

电路中的电流I===0.3A,

R1两端的电压U1=IR=0.3A×5Ω=1.5V,

(2)由(1)知R1两端的电压U1==,即与U1与R的关系不是成正比的,反映在刻度上是不均匀的.而电压表的刻度是均匀的.

完形填空
请阅读短文,并根据所读内容在文章后表格中的空格里填入一个最恰当的单词。
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Celebrating Sleep
World Sleep Day, observed on 21 March, was created to bring attention to the growing number of sleep problems worldwide. Sleep is a natural part of human life, but many people in the modern world ignore its importance. As a result, sleep problems are increasingly common.
In 2002, scientists at the University of Athens in Greece conducted a survey of over 35,000 people in 10 countries around the world, including China, Belgium and South Africa. Of the people that responded to the survey, 24 percent said that they did not sleep well, and based on their responses, 31.6 percent were diagnosed with insomnia and another 17.5 percent were diagnosed with borderline insomnia(失眠). In addition, 30.7 percent of survey respondents reported visiting a doctor for help with sleep problems and 11.6 per cent said that they felt very sleepy during the day.
Overall, the survey found that many people suffer the effects of poor quality sleep, some examples of which are being unable to fall asleep and waking up in the middle of the night. The main factors causing these problems are pressure from school or work and a fast pace of life, but noise pollution and light pollution also interfere with sleep and contribute to poor quality sleep. The survey’s findings are particularly troubling because large numbers of people were found to have difficulty sleeping at night. The short-term effects of this are tiredness and trouble concentrating. If this happens for a long time, the risk of gaining weight and having a heart attack may increase.
There are many things you can do to improve the quality of your sleep. First, you should have regular sleep habits. Try to go to bed and wake up around the same time each day. You also need to make your bedroom a cool, dark, quiet place to sleep so that heat, light and noise do not disturb you. At night, you should also avoid things that contain caffeine, such as chocolate, coffee, tea and many soft drinks, as caffeine may keep you from sleeping.
Getting a good night’s sleep is important for everyone. By following the advice above, you can rest better at night and work better during the day.
Title: Celebrating Sleep
Topic
Context
 
World Sleep Day
Due to __3___of sleep problems, people observed Mar. 21, World Sleep Day, bringing attention to the importance of sleep.
 
Responses of the survey
◆Of 3, 5000 people in 10 countries in the world, there were 24 percent of the people saying they didn’t sleep well.
◆31.6 percent were diagnosed with insomnia and another 17.5 percent were on the  _4___ of sleeplessness.
◆The __5__ of the people feeling sleepy during the day is 11.6.
◆30.7 percent reported__6___ to a doctor for sleep problems.
 
__1___causing sleep problems and their
consequences
◆Under _7____ from school or work, people may have sleep problems.
◆A fast pace of life causes sleep problem as well.
◆Poor quality sleeps also ___8__ from noise or light pollution.
◆There is much __9___ that sleepless people easily gain weight and have a heart attack.
◆Feeling tired and sleepy, people find it hard to concentrate.
___2__ to take to improve sleep quality
◆Have regular sleep habits
◆Make your bedroom cool, dark and quiet
◆Avoid things ___10___caffeine
 
单项选择题