题目

  What is the first thing you notice when you walk into a shop? The products displayed(展示)at  the entrance? Or the soft background music? But have you ever noticed the smell? Unless it is bad，the answer is likely to be no．But while a shop’s scent may not be outstanding compared with sights and sounds，it is certainly there．And it is providing to be an increasing powerful tool in encouraging people to purchase． A brand store has become famous for its distinctive scent which floats through the fairly dark hall and out to the entrance via scent machines．A smell may be 在“测量小灯泡的电阻”的实验中，电源电压为3V，小灯泡的额定电压为2.5V，阻值为10Ω左右，滑动变阻器上标有“20Ω  1A”字样．（1）请你在下图中用笔画线代替导线完成电路连接．（2）在连接电路时，开关应处于______状态，开关闭合前，滑动变阻器的滑片应移动到______（选填“A”或“B”）端．（3）闭合开关后，发现小灯泡不发光，电流表无示数，电压表的示数接近电源电压，则产生这一故障的原因是______．（4）排除故障后，调节滑片P，使小灯泡正常发光，电表的示数如图所示，则电压表的示数为______V，电流表的示数为______A，小灯泡正常发光时的电阻为______．