# PHY lab 9 - PHY-132 Current BalanceJoshua Manski Partner:...

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PHY-132 Current Balance- Joshua Manski Partner: Sandra Thoms Date: October 30 th 2008 SLN# 82129, Thursday 12:00pm Brian Morrison Objectives : The purpose of this lab was to examine how gravitational force is counteracted by currents that are running antiparallel. By studying the relation between current, gravitational force, and magnetic fields we collected data that allows us to estimate the value for the permeability of free space. The connection between force and magnetic fields would help us with all our data taking and analysis. Finally, we hoped to see how other magnetic fields such as earth’s would affect our experiment. Experimental Procedure : In this experiment we worked with a current balance device that consisted of a voltage source, a resistor, and a circuit that would allow for two currents that were going in opposite

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directions to come close to each other. When the currents were antiparallel, the top current was balanced so that there were a few millimeters separating them. The top one was balanced over the bottom by placing it on a pivot point and adjusting how it sat on this pivot. There was a lever so that we could re-calibrate the balancing device once it was set. See the figure below for the schematic of this set up. The second apparatus that we needed was a way to accurately tell the difference between the two bars while they were balancing. We used a scope that was attached to a ruler at a fixed distance away from the above circuit. Using the scope we were able to look through it at a mirror that was attached to the balancing contraption for the top current wire. The mirror then reflected the crosshairs of the scope back to the ruler that the scope was attached to. This way we could see how much the top current wire moved when we applied a current to it. See the figure below for a drawing of this set up.
To begin this experiment we needed to take down some initial measurements. We needed to measure the distance between the mirror and the point at which the crosshairs rested on the ruler, and the actual distance between the mirror and the top current wire. We then focused the scope so that one person in the group could see crosshairs while eliminating parallax. This same person took all measurements so that we never needed to calibrate it again. Once the scope was calibrated we placed a 500g weight on the top current wire so that the bars were touching. We noted the measurement on the ruler viewed through the scope. Then we took off the weight and noted the measurement on the ruler when our system was in balance. We used this measurement to compare to for the rest of the lab. Now that all our preliminary data was taken we started the lab. We added five sets of

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## This note was uploaded on 09/20/2010 for the course PHY 132 taught by Professor Tsen during the Spring '10 term at University of Arizona- Tucson.

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PHY lab 9 - PHY-132 Current BalanceJoshua Manski Partner:...

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