问题 选择题

如图所示电路中,电源电动势为E、内阻为r,电阻R1R2为定值电阻,R为滑动变阻器,A、B为电容器的两个极板,电压表和电流表均为理想表,电源负极接地。现闭合电建K,把变阻器的触头滑到变阻器R的中点位置,而后在A、B两板间放入某带电油滴,油滴恰能静止在A、B两板中间。则下列说法中正确的是

A.仅把A极板缓慢向上移动,使A、B间距离增大, A板对地的电势将升高

B.仅把B极板缓慢向上移动,油滴将向上运动

C.当把滑动变阻器的触头由中点缓慢滑到b端时,电压表和电流表读数都变大

D.仅把电键K断开,油滴有可能继续静止在A、B两板中间

答案

BC

由于两板间电压不变,故A板对地的电势不变,A错误;当电压一定时,B极板缓慢向上移动,电场变大,油滴将向上运动,B正确;触头由中点缓慢滑到b端时,总电阻变大,总电流减小,内电压变小,外电压变大,电压表示数变大,由于R1两端电压变小,则R2两端电压变大,电流变大,C正确;当电键K断开,极板电量通过电阻R2放电,则油滴下落,D错误。

选择题
阅读理解

阅读理解。

     Advice to "sleep on it" could be well founded, scientists say. After a good night's sleep a problem that

couldn't be solved the night before can often appear more manageable, although the evidence until now

has been anecdotal (个人体验的).But researchers at the University of Luebek in Germany have designed

an experiment that shows a good night's sleep can improve insight (顿悟) and problem-solving.

     "If you have some newly-got memories in your brain, sleep acts on these memories' restructures them,

so that after sleep the insight into problem which you could not solve before increases," said Dr Jan Born,

a neuroscientist (神经科学家), at the university. To test the theory, they taught volunteers two simple

rules to help them turn a string of numbers into a new order. There was also a third, hidden rule, which

could help them increase their speed in solving the problem. The researchers divided the volunteers into

two groups: half were allowed to sleep after the training while the rest were forced to stay awake. Dr Jan

Born and his team noticed that the group that had slept after the training were twice as likely to figure out

the third rule as the other group."Sleep helped," Born said in a telephone interview. "The important thing is

that you have to have a memory representation in your brain of the problem you want to solve and then

you sleep, so it can act on the problem." But Born admitted that he and his team don't know how

restructuring of memories occurs or what governs it. Pierre Maquet and Perrine Ruby of the University of

Liege in Belgium said the experimental evidence supports the anecdotal suggestions that sleep can help

develop creative thinking. Although the role of sleep in human creativity will still be a mystery, the research

gives people good reason to fully respect their periods of sleep, they added.

1. The underlined phrase"sleep on it" in Paragraph 1 probably means _____.

A. to delay deciding something until the next day

B. to get as much sleep as possible

C. to go on sleeping without being disturbed

D. to sleep till after the time you usually get up in the morning

2. Jan Born and his team carried out the experiment through _____.

A. comparison

B. interview

C. survey

D. imagination

3. It can be inferred from the passage that ______.

A. people should sleep so long as they have time

B. sleep is the only way to solve hard problems

C. people have various periods of sleep

D. people know how sleep reconstructs memories

4. What would be the best title for the passage?

A. How Sleep Works

B. Sleep Helps Solve Problems

C. No Evidence, But Well Founded

D. Born's Discovery On Sleep