es3_lab1 - Tufts University School of Engineering...

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Tufts University School of Engineering Department of Electrical and Computer Engineering ES3 - Introduction to Electrical Circuits Fall 2007 Lab Section: Thursday 8:30-10:30am Experiment 1 DC Measurements Name: Teddy Portney [email protected] tufts.edu Submitted to: Bertan Hallacoglu Experiment Performed: September 27, 2007
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Experiment Due: October 4, 2007 I. PURPOSE The purpose of this lab was to gain an understanding of how to measure DC currents, DC voltages, and electrical resistance. We learned how to use several common laboratory devices, namely a multimeter and a DC power supply. II. INTRODUCTION In the electrical world, there are two kinds of current, direct current (DC) and alternating current (AC). The simpler of the two is DC by far, which is why we begin our laboratory experimentations with this. Also, there is no such thing as zero resistance. In class, we have always assumed that a plain conductor, or metal wire, has zero resistance, as this greatly simplifies problems when beginning circuit theory. However, even this plain conductor has a small resistance. The formula for this resistance is given as R=ρL/A, where R is the resistance, L is the length of the wire, A is the cross-sectional area of the wire, and ρ is the resistivity constant of the wire. This constant varies depending on what material(s) the wire is made from. I. MATERIALS AND EQUIPMENT For this lab, we used several common laboratory devices. We used a regulated DC power supply, as well as a multimeter. A multimeter is one machine that contains each of the following: a voltmeter, an ammeter, an ohmmeter, and a frequency counter. We also used several different types of resistors. We used a normal 1kΩ electrical resistor, as well as an NTC-102 thermistor, or a resistor whose resistance varies as a function of the temperature. Then, there was the photocell, also known as a photoresistor, whose resistance varies as a function of the amount of light it is receiving. Lastly, there was a potentiometer, or a resistor whose resistance varies depending on the location of a movable wiper inside the device. Finally, there was an audio speaker, a device which consists of a large magnet, a coil of wire, and a speaker cone which moves according to the magnetic field produced by the coil of wire and the magnet. III. PROCEDURE This lab consisted of many short parts, each one corresponding to one of the devices listed above. In the first part, we connected a multimeter to the different outputs of the DC power supply. First, we tested the lead labeled 5V. Then we tested the lead labeled -1.5 to -15V, and set it to approximately -12 volts. Then we connected these two in series and measured the resultant voltage.
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