题目

    Jack went to a barber’s shop and had his hair cut. But when he  ____1  out，he was not happy  __2__ the result．When his friend Bob saw him，he laughed and said。“What has happened to your hair。Jack?’’ Jack said．“I tried a new barber’s shop today， __3__  1 wasn’t quite satisfied with my old one，but this one seems  ___4___ worse．”     Bob agreed，“Yes，I think you’re right，Jack． Now I’ll tell you __5  to do when you go into a barber’s shop next time：look at all the barbers’ hair，find out whose hair 1ooks  6__  ，and th如图所示的电路中，电源电压不变，小灯泡的额定电压为2.5 V，滑动变阻器的最大阻值R为定值电阻R0的三倍.闭合开关S，当滑片P置于某点时，电压表示数为2.5 V，电流表示数为I1 ， 当滑片P置于最右端时，电流表示数为I2 ， 且I1∶I2＝5∶4.两次变阻器连入电路的电阻之比R1∶R＝8∶15.如图是该小灯泡I－U图象.求：（1）小灯泡正常发光时的电阻值.（2）滑片置于最右端时，小灯泡的实际功率.？（3）电源电压.？