A 1.60 m cylindrical rod of diameter 0.550 cm is connected to a power supply tha
ID: 1865907 • Letter: A
Question
A 1.60 m cylindrical rod of diameter 0.550 cm is connected to a power supply that maintains a constant potential difference of 13.0 V across its ends, while an ammeter measures the current through it. You observe that at room temperature (20.0 ?C) the ammeter reads 18.2 A , while at 92.0 ?C it reads 17.1 A . You can ignore any thermal expansion of the rod.
a. Find the resistivity for the material of the rod at 20 ?C.=
??m <-- this is a, I need b
b. Find the temperature coefficient of resistivity at 20 ?C for the material of the rod.____ (?C)?1
? = 1.06×10?5??m <-- this is a, I need b
Explanation / Answer
a)
Resistance at T=20oC is
Ro=V/Io =13/18.2 =0.714285714 ohms
Area
A=pi*d2/4 =pi*(0.55*10-2)2/4 =2.37583*10-5 m2
Since
Ro =pL/A
0.714285714 =p*1.6/(2.37583*10-5)
p=1.06*10-5 ohms
b)
Since Resistance at T=92oC
R=13/17.1 =0.7602 ohms
Resistance variation with temperature is given by
R=Ro[1+alpha*(T2-T1]
0.7602 =0.7143 [1+alpha*(92-20)]
alpha =8.934*10-4 /oC
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