In the interval between the freezing point (ice point) of water and 700.0deg-C,
ID: 1499108 • Letter: I
Question
In the interval between the freezing point (ice point) of water and 700.0deg-C, a platinum resistance thermometer is to be used for interpolating temperatures from 0 °C to the melting point of zinc, 692.666 K. The temperature, in Celcius or Centigrade, is given by a formula for the variation of the resistance of the thermometer with temperature: R = R,o(1 + A Tc + B Tc2). Ro, A, and B are constants determined by measurements at the ice point, the steam point, and the melting point of zinc.
If R equals 7.22790 ohms at the ice point, 55.43799 ohms at the steam point, and 177.50209 ohms at zinc's melting point, find Ro.
What is A?
What is B?
Explanation / Answer
R = Ro(1 + A Tc + B Tc2)
=> At ice point of water
=> 7.22790 = Ro(1 + 0)
=> Ro = 7.22790 ohm
=> at the steam point
=> 55.43799 = 7.22790(1 + 100A + 10000B)
=> 48.21 = 722.79A + 72279B
=> at zinc's melting point
=> 177.50209 = 7.22790(1 + 419.516A + 175993.67B)
=> 170.274 = 3032.219A + 1272064.647B
=> A = 0.07 ohm/degree-celsius
=> B = - 3.3002 ohm/(degree-celsius)2
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