A thermocouple is a temperature-measurement device that consists of two dissimilar metal wires joined at one end. A voltage generated at the metal junction is read on a potentiometer or millivoltmeter. When certain metals are used, the voltage varies linearly with the temperature at the junction of the two metals:
V (mV) = aT (oC) + b
An iron-constantan thermocouple (constantan is an alloy of copper and nickel) is calibrated by inserting its junction in boiling water and measuring a voltage V = 5.27 mV, and then inserting the junction in silver chloride at its melting point and measuring V = 24.88 mV. Derive the linear equation and convert it to an equation for T (oF) in terms of V (mV).