4bl-lab3 - Ross Miller 503290136 Lab 3: DC Circuits...

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Ross Miller 503290136 Lab 3: DC Circuits Partners: Sam Ahn and Andre Svadjian TA: Steve Suh Session 6
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Introduction: The purpose of this experiment was to teach the students about DC circuits. Topics in DC circuits to be looked at are current, voltage drop, capacitance, resistance, Ohm’s law, diodes, conductivity. Theory: We began by examine currents against voltages to get resistances, using a graph to find out the resistance, because the slope of the current against voltage line will be 1/R. This is done to validate Ohm’s law, the equation I=V/R . I is of course current here and V is voltage, R was to be found using the reciprocal of the graph, meaning the smaller R is, the more vertical the line will be. Next we looked at diodes and studied their properties. Silicon diode behavior should allow that in one direction if a voltage above .4 to .7 is exceeded, there is almost no resistance. Zener diodes should act like a silicon diode in one direction while allowing increasing current to pass as the voltage in the negative direction is increased past a threshold point in the other direction. Light emitting diodes were to be measured and calculated. The amount of power used by the LED can be found by the equation P=IV, but the numbers we have are not necessarily accurate for the LEDs we are actually using numbers that aren’t necessarily specific to this LED. We now try to look at the effect temperature has on resistances. For a lightbulb, as well as many other resistors, their resistance increases as their temperature increases. We set the wave generator to slowly increase the voltage over a longer period of time than with the other resistors and watch to see what the resistor does. Right about now we got to have some fun and look at the conductivity of matter. We took a large spool of wire and measured its resistance with a multimeter and using the data we have about the spool we are going to compare it to the data obtained from the equation R=L/σA=ρL/A holds true. Doing research on 24 AWG wire I was able to learn that AWG Feet/Ohm Ohms/100ft Ampacity* mm^2 Meters/Ohm Ohms/100M 24 19.1 5.24 1.3 0.511 5.82 17.2 conductor size 24 AWG area 0.205 mm^2 (square-mm) area 404.0 CM (circular mil) diameter 20.1 mil (1)
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diameter 0.511 mm (1) DC-resistance 0.0842 Ohm/m tensil strength 6.14 kgf (2) weight 1.820 kg/km (Cu) weight 0.553 kg/km (Al) Resistivities at room temp: Element Electrical resistivity (ohm-m) Copper 1.678e-8 So in theory .5 pounds of 818 feet per pound wire should be about 414 feet long, which converts to 126 meters, the area size is .205mm^2 which equals 2.05e-7 m^2, and we are supposed to be looking for the conductivity of copper. Solving R=L/σA for σ we get σ=L/RA. We are testing to see if this equation holds true and will give us an accurate measurement of the conductivity of copper, which is the inverse of the resisitivity and should be around 5.95e7/(ohm meter)at room temperature. For the conductivity of water we are sticking two metallic cylinders in the water and
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This note was uploaded on 11/12/2010 for the course PHYSICS 318017201 taught by Professor Carter during the Spring '10 term at UCLA.

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4bl-lab3 - Ross Miller 503290136 Lab 3: DC Circuits...

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