Temperature vs. Resistivity
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Understanding science requires that you understand the correlation of the laws, measurements, and theorems. You can be shown an equation, but to fully understand how it works you will need to know what it means, and how adjusting the equation will affect all the variables. Ohms law states that Resistance in a current can be found by dividing Voltage by Current. If the voltage increases and the current lowers, then the total resistance will increase. This knowledge is very helpful when trying to build circuits for a school project or for your career. However, it is helpful to know a correlation between all the variables that a situation like Ohms law will create. When voltage or current is created, there must be heat, or temperature. What will happen when you create a circuit that has high resistance, will the wire be scorching hot, or will it be cool enough to touch? If you choose to study science in school, being able to identify how temperature relates to resistance immediately will further your ability to be a successful student.
In this lab, I will create an experiment that will record the temperature and resistance at different amounts of Current. I predict that if I increase the current in a wire, the temperature and resistance will increase. This should mean that that energy from the heat of the wire creates a certain amount of resistance. I also believe that as the current increases, the increasing temperature will dissipate more heat, causing the resistance to increase by a larger scale.
Here is a diagram of the lab, and here is how it works: In the center is a standing clamp that is holding up a thin glass tube. Wrapped around the tube is a microwave wire, that is attached to other wires that are then attached to either the voltmeter or the ammeter. The meters read the volts or current running through the wire, but the power supply is the unit that controls how much electricity that flows through the wires. Wrapped around the wire are several layers of fiberglass insulator. I choose fiberglass because it can safely touch the heated wire without bursting into flames. Also, notice the wire inserted into the middle of the tube. That is one of the wires which attach to the thermocouple. The other wire leads into four foam cups full of ice water. The thermocouple is then attached to the computer.
To take all the data I need, I need to record voltage, current, resistance and the temperature. Since I have the voltmeter and ammeter plugged in, I can easily record the voltage and current. Ohms law states that resistance equals voltage divided by current. By using this formula, I can derive the resistance from the wires. The last thing I need is to record temperature. The thermocouple is a device that finds the difference in temperature between its two wires, and records the information on a computer. Since one wire is inside a cup of ice water (zero degrees) and the other is taking heat from the wire, the thermocouple derives this equation: Temp - 0 = Temp. Once I am able to control the current, and use the ammeter to record voltage and current, and have the thermocouple working on the computer, I will fill in a data table of my variables, like I have done below.
The results of this graph show that as temperature increases, so does the resistance. This graph is not completely steady, for several reasons. The current that was used was not raised by a constant amount. Therefore the temperature would rise either more or less depending on whether the current was increased by .1 amps or by .2 amps. Another factor that affected the graph was the stability of the current running through the wires. At several points the current was set to a certain amount, and while recording the temperature, the current would occasionally boost up by around .3 to .4 amps. This would cause the temperature to jump, along with the voltage and current. At one point in the experiment, I had to tighten the fiberglass around the tubing as the heat had caused it to fluff out, and while doing so I readjusted the placement of the thermocouple wire. This caused the temperature readings to be different, and caused the graph to slump then raise again.
The analysis of this experiment shows a relationship between temperature and resistance. It appears that the increase in temperature will usually indicate an increase in resistance. My hypothesis was correct, however I had predicted that the resistance would increase at much larger intervals, when in fact it increased by very small intervals. At certain points, temperature increased but the resistance barely changed. There was never a point when temperature would go down, suggesting some of the resistance is dissipated through the high temperature it faced. As the graph on the results page will show, there is a large drop in resistance during the experiment. Fortunately this happened, for it does show that the resistance increases even when other variables are affecting the current. Perhaps the wires were plugged in differently and caused a slight increase in resistance, and once it was moved it corrected itself. It is possible that the meters were malfunctioning as well. Of course these mistakes give examples for improving the experiment. More accurate readings of voltage and current would help, and being able to manipulate the actual current running through to very precise measurements would help. As for improving the temperature, it would be helpful to create a fully stable zero degree temperature, and to be able to place the wire and tubing into a better insulator that is not affected by the surrounding room temperature.
http://spiff.rit.edu/classes/phys273/manual/temp_coeff.html - Another lab experiment studying the same concepts
http://eo.ucar.edu/skymath/tmp2.html - Basic knowledge and understanding of Temperature
http://230nsc1.phy-astr.gsu.edu/hbase/electric/resis.html - Want to calculate resistivity on your own? Try out this link
http://chem.ch.huji.ac.il/~eugeniik/instruments/test/voltmeters.htm - Information about the voltmeter used in the lab
http://www.school-for-champions.com/science/thermalinsulation.htm - Details on insulation and why fiberglass was a good insulator choice