题干

如图所示,平行板电容器与电动势为E′的直流电源(内阻不计)连接,下极板接地,静电计所带电荷量很少,可被忽略.一带负电油滴被固定于电容器中的P点.现将平行板电容器的上极板竖直向下平移一小段距离,则下列说法正确的是(   )

A:平行板电容器的电容将变小

B:带电油滴的电势能将减少

C:静电计指针张角变小

D:若将上极板与电源正极断开后再将下极板左移一小段距离,则带电油滴所受电场力不变

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B

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    Camping wild is a wonderful way to experience the natural world and, at its best, it makes little environmental influence. But with increasing numbers of people wanting to escape into the wilderness, it is becoming more and more important to camp unobtrusively(不引人注意地)and leave no mark.

    Wild camping is not permitted in many places, particularly in crowded lowland Britain. Wherever you are, find out about organizations responsible for managing wild spaces, and contact them to find out their policy on camping and shelter building. For example, it is fine to camp wild in remote parts of Scotland, but in England you must ask the landowner's permission, except in natural parks.

    Camping is about having relaxation, sleeping outdoors, experiencing bad weather, and making do without modern conveniences. A busy, fully-equipped campsite(野营地)seems to go against this, so seek out smaller, more remote places with easy access to open spaces and perhaps beaches. Better still, find a campsite with no road access: walking in makes a real adventure.

    Finding the right spot to camp is the first step to guaranteeing a good night's sleep. Choose a campsite with privacy and minimum(最小化的) influence on others and the environment. Try to use an area where people have obviously camped before rather than creating a new spot. When camping in woodland, avoid standing dead trees, which may fall on a windy night. Avoid animal runs and caves, and possible homes of biting insects. Make sure you have most protection on the windward side. If you make a fire, do so downwind of your shelter. Always consider what influence you might have on the natural world. Avoid damaging plants. A good campsite is found, not made—changing it should be unnecessary.