Question

（1）测某金属丝的电阻率，为了精确的测出金属丝的电阻，需用欧姆表对金属丝的电阻粗测，如图是分别用欧姆档的“×1档”（图a）和“×10档”（图b）测量时表针所指的位置，则测该段金属丝应选择             档（填“×1”或“×10”），该段金属丝的阻值约为                                                                                                     Ω．

                   

（2）所测金属丝的直径d如图c所示，d=                                                            mm；接入电路金属丝的长度L如图d（金属丝的左端与零刻度线对齐）所示，L=                                                               cm．

（3）为了更精确的测量该段金属丝的电阻，实验室提供了如下实验器材：                  

A．电源电动势E（3V，内阻约1Ω）                                                                           

B．电流表A₁（0～0.6A，内阻r₁约5Ω）                                                                     

C．电流表A₂（0～10mA，内阻r₂=10Ω）                                                                    

D．电压表V（0～15V，内阻约3kΩ）                                                                         

E．定值电阻R₀=250Ω                                                                                                  

F．滑动变阻器R₁（0～5Ω，额定电流1A）                                                                 

G．滑动变阻器R₂（0～150Ω，额定电流0.3A）                                                          

H．开关，导线若干                                                                                                     

请根据你选择的实验器材在如图e的虚线框内画出实验电路图并标明所选器材的字母代号．                     

（4）若所选电表A₁、A₂的读数分别用I₁、I₂表示，根据你上面所设计的实验电路，所测金属丝的电阻的表达式为R=                                                                                                           ，若所测电阻值为R，所测金属丝电阻率的表达式为ρ=                                                                                                                   （用R、L、d表示）．

                                                                                                                                   

Answer 1

（1）×1，7.0；

（2）1.750，98.02；

（3）如图；

（4）；．