题目

Driving to a friend’s house on a recent evening, I was attracted by the sight of the full moon rising just above my friend’s rooftop. I stopped to watch it for a few moments, thinking about because we spend most of our lives indoors.My friend had also seen it. He grew up living in a forest in Europe, and the moon meant a lot to him then. It had touched much of his life.I know the felling. Last DecemberI took my seven-year-old daughter to the mountainous jungle of northern India with some friends. We stayed in a forest rest house with no electricity or running hot water. Our group had campf（2004?北京）为了测定电流表A1的内阻，采用如图1所示的电路．其中：A1是待测电流表，量程为300μA，内阻约为100Ω；A2是标准电流表，量程是200μA；R1是电阻箱，阻值范围0～999.9Ω；R2是滑动变阻器；R3是保护电阻；E是电池组，电动势为4V，内阻不计；S1是单刀单掷开关，S2是单刀双掷开关．（1）根据电路图1，请在图2中画出连线，将器材接成实验电路（2）连接好电路，将开关S2扳到接点a处，接通开关S1，调整滑动变阻器R2使电流表A2的读数是150μA；然后将开关S2扳到接点b处，保持R2不变，调节电阻箱R1，使A2的读数仍为150μA．若此时电阻箱各旋钮的位置如图3所示，电阻箱R1的阻值是86.386.3Ω，则待测电流表A1的内阻Rg=86.386.3Ω．（3）上述实验中，无论怎样调整滑动变阻器R2的滑动端位置，都要保证两块电流表的安全．在下面提供的四个电阻中，保护电阻R3应选用：BB（填写阻值相应的字母）．A.200kΩ    B.20kΩ      C.15kΩ      D.20Ω（4）下面提供最大阻值不同的四个滑动变阻器供选用，既要满足上述实验要求，又要调整方便，滑动变阻器CC（填写阻值相应的字母）是最佳选择．A.1kΩ      B.5kΩ      C.10kΩ     D.25kΩ