hüs5 - TEMPERATURE MEASUREMENT...

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TEMPERATURE MEASUREMENT Objective : By using thermocouples to conduct temperature measurement. Apparatus : 1. Vertical tube furnace. 2. Thermocouple. 3. Thermocouple. 4. Potentiometer. 5. Mercury in glass thermometer. Sample : Tin (Sn) was used but its exact composition is not known. Results and Discussion : We have found the melting point of Sn by measuring the thermo-emf between the thermocouple ends. We have found the melting point 226 ° C but the melting point of pure Sn is 232 ° C. This shows that our sample is not pure. We can also understand this from the cooling curve of Sn that we have drawn because you can observe the supercooling from the graph. Supercooling is the process of chilling a liquid below its freezing point , without its becoming solid . A liquid below its melting point will crystallize in the presence of a seed crystal or nucleus around which a crystal structure can form. However, lacking any such nucleus, the liquid phase can be maintained all the way down to the
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temperature at which dynamic arrest occurs, and the liquid solidifies into an amorphous -- that is, non-crystalline – solid. We have taken emf values from the computer to find the melting point of Sn. We have not calculated the melting point directly because the emf values we have taken are accordind to the cold junction temperature of 24 ° C. In order to find the real temperature we have made correction according this formula : mV 1 0 ° C T 1 mV 2 mV 3 RT mV 1 = mV 2 + mV 3 In this experiment, mV 1 is 0,98 because RT is 24 ° C. We have found the melting point of Sn by using thermocouples. The principle of thermocouples depends on Thomson - Peltier effect. The Peltier Effect : The Peltier effect is the reverse of the Seebeck effect; a creation of a heat difference from an electric voltage. It occurs when a current is passed through two dissimilar metals or
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hüs5 - TEMPERATURE MEASUREMENT...

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