题干

某学生用如图a所示电路测金属导线的电阻率,可供使用的器材有:

被测金属导线ab,电阻约10Ω,导线允许流过的最大电流0.8A,稳恒电源E,电源输出电压恒为E=12V,电压表V,量程为3V,内阻约5KΩ,保护电阻:R1=l0Ω,R2=30Ω,R3=200Ω.刻度尺、螺旋测微器,开关S,导线若干等

实验时的主要步骤如下:

①用刻度尺量出导线ab的长度l,用螺旋测微器测出导线的直径d.

②按如图a所示电路将实验所需器材用导线连接好.

③闭合开关S,移动接线触片P,测出aP长度x,读出电压表的示数U.

④描点作出U﹣x曲线求出金属导线的电阻率ρ.

完成下列填空:

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    Exercise!Get off the couch and get moving. Being active and healthy can give you a completely different attitude to life.

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