题干

在图(a)所示的电路中,电源电压为6伏且保持不变,电阻R1的阻值为30欧,滑动变阻器R2上标有“50Ω  2A”字样.

①求通过电阻R1的电流I1

②若在电路中串联两个电流表,闭合电键后电流表示数如图19(b)、(c)所示,求此时变阻器连入电路的阻值.

上一题 下一题 0.0难度 选择题 更新时间:2018-04-24 08:56:49

答案(点此获取答案解析)

解:①通过电阻R1的电流I1为:I1= U/ R1=6V/30Ω=0.2A;②当电流表A1接R1支路,电流表A2接R2支路时,I2=0.16A, R2= U/I2=6V/0.16A=37.5Ω;当电流表A1接R1支路,电流表

同类题4

完形填空

    There are purple clothes, purple handbags, purple bicycles, purple furniture, even purple computers! So purple is one of the most1colors today. But in the past, purple was a very expensive and unusual color. Let's take a look at the rich2of the color purple.

    Some scientists believe that the first plants to appear on Earth over 500 million years ago3looked purple, not green. Plants today are green because4use green chlorophyll (叶绿素) to produce energy.5these early plants probably used something called retinal, which is a dark purple color.

    During the time of the roman Empire (37 BC-476 AD), it was very6to make purple dye (染料). The dye came from sea snails (海螺) .But10.000 dead sea snails7you just one gram (克)of purple dye… as well as a very bad smell! This8purple dye was called Tyrian purple, and it was the preferred9of emperors.

    In 16th--century England, purple was10for the king's family members. Queen Elizabeth Is clothes were purple, but ordinary people were not allowed to11the color.

    In 1856. William Perkin, an 18-year-old12student, noticed something strange while doing an experiment (实验). The chemicals (化学药品) he used to clean his instruments13with the chemicals he used in his experiment and produced a bright purple color. This14Perkin to start a company using this chemical mixture to make purple dye. The dye was much15than sea snail dye. Thanks to Perkin, now anyone can afford to wear purple clothes.