如图是利用滑动变阻器控制电流的电路，其中电阻R 为100 欧姆，它与滑动变阻器串联在电路中，通过电阻的电流可在10 毫安～100 毫安范围内调节。
（1）选用电源的电压应为多大？
（2）变阻器的总电阻为多大？额定电流至少要多大？
（3）上述电路能否使电阻R两端的电压调为零？请说明理由。
解：
（1）由于电阻R 的大小为100 Ω ，当滑变接入为0 Ω 时，电流表示数最大为100 毫安，则电源电压为U=RI=10V；
（2）当滑动变阻器最大时，电流表示数最小，
则R 总=U/I=10V/0.01A=1000 Ω，
R滑=R总-R=1000-100-900Ω
由于电流表可在10 毫安～100 毫安范围内调节，则滑动变阻器的额定电流至少需要100 毫安。
（3）不能，由U=
可知当R 滑增大时，U 将减小，当R 滑达到最大值900 欧时，U 取到最小值1V ，不能取到0。
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| As we know, museums are buildings where many valuable and important objects are kept so that people can go and see them. For example, art museums are places where people can learn about 9 (1) v______ cultures. More and more popular "design museums" that are opening today, however, perform quite a different role. (2) U______ most art museums, the design museum shows objects that are easily found in our daily life, such as fridges and washing machines. The (3) a______ of design museums is that they are places where people feel familiar with the exhibits(展品).Being different from the art museum visitors, design museum visitors (4) s______ feel frightened or puzzled. This is partly because design museums clearly show how and why mass-products (批量产品) work and look as they do, and how design has (5) i______ the quality of our lives. Art museum exhibits, on the other hand, would most probably fill visitors with a feeling that there is something (6) b______ their understanding. Several new design rnuseums have opened their doors in (7) r______years. Each of these museums has tried to satisfy (满足) the public's growing interest in the field with new (8) i_____. London's Design Museum, for example, shows a collection of mass-produced objects from electric typewriters to a group of Italian fish-tins. The choices open to design museums seem (9) f_______ less strict than those to art museums, and visitors may also sense (感觉到) the humorous part of our society while walking around such exhibits as interesting and unusually attractive toys (10) c______ from our everyday life. | |
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