A homemade thermostat uses a probe consisting of a cylindrical chunk of copper m

Question

A homemade thermostat uses a probe consisting of a cylindrical chunk of copper metal to monitor the temperature of a water bath used for cooking poached eggs. The thermostat measures the water temperature applying a constant voltage across the copper so that a current passes through it and then measuring the magnitude of this current. The ideal temperature for cooking the eggs is 185F If the thermostat measures a current of 1.00 × 10^2 mA when the probe is sitting at room temperature (70 F), what should the measured current be when the water is at the correct temperature?

Explanation / Answer

temperature coeeficient of copper = 0.00404 / degree celsius

deltaT is in degree celsius, degree celsius = (F - 32)*5/9

i1/i2 = R2/R1 = 1 + Alpha*deltaT = 1 + 0.00404*63.89 = 1.258

=> i2 = i1/1.258 = 1.0*10^-2 /1.258 =0.794*10^-2 mA

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