﻿ Electrical Resistivity

# background

By connecting the two ends of a wire to a positive and negative terminal of a batter, a flow of electrons is created, for there is a difference in electrical potential. Current, in amperage, is the measurement of the flow of electrons(hyperphysics), and the equation that represents this flow is Ohm's Law. Ohm's Law is current equals voltage over resistance. Voltage is measured in volts and describes the difference in charge. Resistance describes how the electrons collide with one another impeding flow , and it is measured in ohms. In most electronics, while current could be controlled through voltage, it is usually controlled through the altering of the resistance. Most things have an inherent resistance, but it is usually very small, so resistors are utilized to heavily alter the resistance value.(Petervaldivia) The inherent resistance of a wire is determined by a few key factors. One of which is the length of the wire. Another factor is the cross sectional area of the wire. The cross section is inversely proportional to the resistance in the wire. Temperature plays a role in resistance, for when a substance gets hotter, the atoms of the substance speed up, so there is a higher chance that there will be collisions. Collisions are what makes up resistance, so resistance is proportional to temperature Semiconductors and insulators resistivity decrease when temperature increases due to the freeing of electrons. these proportions are know as the temperature coefficient, as they show the numerical relationship between temperature and resistivity.(Boundless) Steel naturally has a high resistance at 9.71 x 10-8 Ohms per meter. Steel is commonly used in as the center for high voltage power lines. Steel melts at a temperature of around 1370C (Kross)

# Statement

This experiment is to test the relationship between temperature and the electrical resistance of steel wire.

# Hypothesis

I think that as the temperature of the steel wire rises, the resistance of the wire will rise, for the particles of the wire will be colliding with the flow of electrons in a more prominent manner variables

# Variables

The temperature of the wire is the independent. The measured resistance of the wire is the depended. The length of the wire and the gauge of the wire are controlled variables. SImilarly, the fiberglass container, multimeters, volt converter, and thermocouple are constant throughout the experiment.

# Method

A piece of Steel wire of at least 4 inches in length is required. Along with, copper wiring to connect parts, a voltage converter, two multimeters, a thermocouple, fiberglass insulation, and a glass tube to place the steel wire within. The two multimeters will be used in two ways; One being an ammeter and the other will be used as a voltmeter. The power converter will supply power to the circuit and will be used to heat the steel wire. The steel wire, which is connected to the power converter, is placed inside a StyroFoam tube that was to keep the temperature inside the tube as level as possible. First the steel wires will be painted with a heat resistive non conductive paint, then the thermocouple is placed within the steel wires. The other end of the thermocouple is placed in a cup of ice water, so that it can provided more accurate results. To control the dependent, the voltage converter will alter the voltage on the wire, so that its temperature will increase. data from the voltmeter and the ammeter will be collected at intervals of temperature. the samples will start at o amps and raise .5 amps for each, so the second will be roughly .5 amps and the third will be roughly 1 amp.

# Analisis

Overall, This experiment was a success, as I was able to gain electrical resistance as temperature rises. We averaged our data points, except the first two since they both had negative change in oms that I speculate are inaccuracies of the measuring device, so that we get a general idea of the growth of the electrical resistance. In other words, we took .349 subtracted .3013 then divided by 277.2 minus 50 which resulted in roughly .00021. Now the .00021 was far away from the .005 of Carbon steel(Ness Engineering). This suggests that this metal was more likely closer to stainless steel at .00094(Ness Engineering). This is still about 1/5 the amount that was expected.

# Validity

The validity of this lab started out well because of the tempts to keep the temperature the same, but ultimately, this lab has inconsistent results. This inconsistency is shown by the negative slope of resistance, for this should not happen with an increase of heat. If i was to do this study again, I would definitely

# Bibliography

1. Boundless. Dependence of Resistance on Temperature. Boundless Physics. Boundless, 21 Jul. 2015. Retrieved 23 Nov. 2015 from https://www.boundless.com/physics/textbooks/boundless-physics-textbook/electric-current-and-resistance-19/resistance-and-resistors-146/dependence-of-resistance-on-temperature-523-5640/
2. http://www.engineeringtoolbox.com/resistivity-conductivity-d_418.html
3. Kross, Brian. "Questions and Answers - What's the Melting Point of Steel?"Questions and Answers - What's the Melting Point of Steel? N.p., 26 Aug. 2011. Web. 01 Dec. 2015.
4. "Electric Current." Hyperphysics.phy-astr.gsu.edu. Hyperphysics, n.d. Web. 1 Dec. 2015.
5. "Resistance and Ohm Law." Petervaldivia. Petervaldivia, 1 Jan. 2015. Web. 01 Dec. 2015.
6. Ness, Richard M. "Ness Engineering Tech Data - Metal / Alloy Resistivity."Ness Engineering. Ness Engineering, 21 Oct. 2014. Web. 19 Jan. 2016.