PHY lab seven

# PHY lab seven - PHY-132 Kirchhoffs Laws Lab 7 Joshua Manski...

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PHY-132 Kirchhoff’s Laws- Lab 7 Joshua Manski Partner: Sandra Thoms Date: October 16 th 2008 SLN# 82129, Thursday 12:00pm Brian Morrison Objectives : The first of this lab’s objectives was to examine Kirchhoff’s rules for loops and junctions. We used some resistors connected in series and parallel to create a circuit that allowed us to test these rules. The second objective of this lab was to teach us how to get the maximum amount of power out of a battery by varying the resistance of the load. We used various test resistances to calculate the optimum resistance for power transfer. Experimental Procedure : To begin this lab we had to construct a circuit consisting of five resistors (two of which were decade boxes), and a voltage source. This circuit was wired as seen in the figure below, with the 800ohm and 220ohm resistances as the decade boxes.

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After this circuit was constructed we measured the resistances of the decade boxes to make sure they were close to the nominal values we needed. We then powered the circuit with V volts from the DC supply. For each resistor we measured the voltage across it using the DMM and made sure to note the polarity of the Voltage on the resistor. After the voltages were noted down we applied Kirchhoff’s loop rule for the loops abcd, cdef, and abcfed. We then connected the DMM in series with each separate resistor in order to measure the current through each one. For junctions c, d, a, and e we used Kirchhoff’s Junction rules to validate our measurements. In part two we built another circuit to analyze how resistance can affect power transfer to that load. This circuit is shown in the figure below. Note how the voltmeter is connected in parallel across R L , and the ammeter is connected in series.
For the resistors we used two decade boxes. R 0 was set to 100ohms and it symbolized the internal resistance of the battery. R L was set to values from 10 ohms to 1280ohms increasing by a factor 2 two each time. For R 0 and all the values of R L we measured the resistances with the DMM to be able to see our error. Then for each value of increasing R L we measured the voltage and current across R L as well as the voltage and current on the way down from 1280ohms. We then obtained the power absorbed across the resistor for each resistance value. Using these data points we were able to plot a graph of power as a function of resistance. And using a fitted curve for the plot we were able to determine the resistance of R L that would allow maximum power

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PHY lab seven - PHY-132 Kirchhoffs Laws Lab 7 Joshua Manski...

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