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Rachel Shimberg Physics 182B September 27, 2023 CQ Resistivity 1. Identify the concepts that are most relevant to this week’s lab. Start by thinking about any laws, theories, equations, or physical phenomena. If there are equations that are important during the week’s lab, write them down and discuss what they mean. Use the lab manual as a resource, but don’t just copy down what is written in the theory section. You are free to use the internet to gather additional information to help in discussing the Theory. In this lab, we explored the idea that electric current is basically the flow of tiny charged particles. We can think of "voltage" as the driving force that makes these charged particles move. As these charges move through a material, they bump into the atoms within the metal wire, kind of like people in a crowded hallway. This bumping slows down the charges because it's like a frictional force pushing against their motion. This property is called the resistivity of the metal. To figure out this resistivity, we did an experiment where we measured the resistance of the unknown wire and made a graph showing how it changes with the wire's length. What we found is that if we keep the wire's length constant, its resistance goes down as its thickness (cross- sectional area) goes up. Ohm's Law was a big part of our experiment. It basically says that the voltage drop across a wire is equal to the current flowing through it times the wire's resistance. Once we found the wire's resistance, we could use a formula, R = ρ L/A, to figure out its resistivity. Here, ρ is just a symbol for resistivity, L represents the length of the wire, and A is the wire's thickness. 2. Identify the experimental parameters and their connection to the laws, theories, equations you described previously. Experimental parameters include independent/dependent variables, measurements taken during the experiment, and observations during tests. Essentially, what did you physically do during the lab? And how does it connect back to the principles of the lab? In our experiment, we measured both the voltage drop and the current to figure out the resistance for various lengths of the wire. To make this happen, we had to adjust the clamps along the wire as we changed its length. After that part was done, we plotted a graph showing resistance on one side and length on the other. When we drew a line that best fit our data on this graph, it turned out to be a straight line. This straight-line result was what we expected because the slope of this line represents the resistivity (ρ) of the material divided by the wire's cross- sectional area. 3. Identify some of the simplifications, limitations, assumptions, that are associated with the concepts you discussed above. Discuss the experimental error that comes with the lab and how it affects your measurements. For example, what were some things that made the measurements you made deviate from the theory you expected? mmm
In this experiment, one of the factors causing uncertainty was how we measured the voltage. We didn't directly attach probes to the wire we were testing. Instead of directly connecting probes to the wire we were testing, we had to route the flow of electrons onto a narrower wire that ran through the PASCO machine for voltage measurement. This setup introduced a consistent source of error throughout our experiment. This error became apparent in our data analysis, specifically in the form of a y-intercept on our graph. Ideally, in a perfectly controlled experiment, this y-intercept should not exist. The graph would start at the origin (0,0), representing a direct relationship between resistance and length without any additional factors affecting our measurements. Despite this limitation, we were still able to approximate the resistivity of the metal we were studying, which was one of the goals of our lab. It's important to acknowledge that there was a small margin of error in our results due to the unreversible method of measuring voltage. This shows the importance of recognizing and accounting for sources of uncertainty in scientific experiments to obtain more accurate and reliable data. 4. Summarize your thoughts from the first 3 questions. Answer the question of, “Why did I measure a specific parameter in a particular way?” What was the ultimate goal(s) of the lab? Connect at least one aspect of the lab to a scenario outside of the lab (real-life application). Finally, what troubles did you run into the lab (if none, then just say that)? In the lab, our main task revolved around calculating resistance. This calculation was achieved by dividing the voltage drop across the wire by the current flowing through it. This concept of resistance is pretty straightforward and provides a foundation for understanding how materials act in electrical circuits. The calculated resistance value played an important role in our experiment as it was the key input for determining the resistivity of the wire. Resistivity characterizes how strongly a material contradicts the flow of electric current. The relationship between resistance and length simplified our experiment. Based on a graphical analysis, we found that resistance and wire length had a linear correlation, so we did not have to conduct countless trials to anticipate the pattern. The goal of our experiment was to identify the type of wire we were working with, and we achieved this by evaluating its resistivity. This was important because it allowed us to understand how different materials conduct electricity, such as designing electrical circuits and determining which materials are suitable for insulation. While we encountered a minor challenge when setting up our computer, we quickly resolved this issue by switching to a different computer. Switching computers allowed us to continue with the experiment without any other occurring problems.
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