问题 问答题

如图1所示,某同学设计了一个测量金属丝电阻率的实验.将直径为d的待测金属丝固定在接线柱a、b上,在金属丝上安一个小金属滑片c,连接好电路,电路中R0是保护电阻(阻值未知).已知电压表的内阻远大于金属丝的电阻,电压表的分流作用可以忽略不计.闭合开关后电流表的读数为I0,调节滑片c的位置,分别测量出长度L及所对应的电压值U,然后作出U-L图象,如图2所示.(1)在图线上取一点P,P点的横坐标值为L0,纵坐标值为U0,由此可得该金属丝的电阻率为______.

(2)用实线连接实验线路图

答案

(1)由欧姆定律可得,电阻丝电阻R=

U0
I0

由电阻定律得:R=ρ

L0
S
L0
π(
d
2
)2
,解得:ρ=
πd2U0
4I0L0

(2)电源、电流表、待测金属丝、保护电阻组成串联电路,由题意知:电压表的内阻远大于金属丝的电阻,电压表的分流作用可以忽略不计,电流表应采用外接法,电路图如图所示.

故答案为:(1)ρ=

πd2U0
4I0L0
;(2)电路图如图所示.

阅读理解

阅读理解。

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