A 1.50m cylindrical rod of diameter 0.500cm is connected to a power supply that
ID: 2089194 • Letter: A
Question
A 1.50m cylindrical rod of diameter 0.500cm is connected to a power supply that maintains a constant potential difference of 17.0 V across its ends, while an ammeter measures the current through it. You observe that at room temperature (20.0 degree C) the ammeter reads 18.7A . white at 92.0 degree C it reads 17.3 A You can ignore any thermal expansion of the rod. Find the resistivity and for the material of the rod at 20 degree C. Find the temperature coefficient of resistivity at 20 degree C for the material of the rod.Explanation / Answer
a)
R0=V/I =17/18.7=0.909 ohms
A=pid^2/4 =pi*(0.5*10^-2)^2/4 =1.96*10^-5 m^2
R0=pL/A
=>p=RoA/L =(0.909)*1.96*10^-5/1.5
=>p=1.19*10^-5 ohm-m
b)
R=17/17.3 =0.9826 ohms
R=Ro[1+alpha*dT]
0.9826 =0.909[1+alpha*(92-20)]
1.09=1+72*alpha
alpha =1.12*10^-3 /oC
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