A platinum resistance thermometer consists of a coil of 0.10-mm-diameter platinum wire wrapped in a coil. (a) What is the length of the wire needed so that the coil’s resistance at 20o C is 25 Ω. The resistivity of platinum at this temperature is 1.0 x 10-7 Ω.m. (b) What is the temperature of this platinum wire when its resistance increases 35% of its initial temperature? The temperature coefficient of resistivity for platinum is 3.92 x 10-3 /o C.
Given:
=0.1 mm=0.0001 m;
=200 C;
=25 Ω, resistance at 200 C temperature;
=1.0 x 10-7 Ω.m, resistivity at 200 C temperature;
=3.92 x 10-3 /o C, temperature coefficient of resistivity for platinum;
here R- resistance of platinum wire at the final temperature;
Find:
a) length of the wire;
b) temperature of the wire;
Solution:
a)
b)
Answer:
a) L=1.96m;
b) t=1090C.
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