# Lab 1 - Tufts University School of Engineering Department...

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Tufts University School of Engineering Department of Electrical and Computer Engineering ES3 - Introduction to Electrical Circuits Fall 2007 Lab Section: Tuesday 2:30 – 4:30 Experiment 1 DC Measurements Name: xxxxxx xxxxxx@ tufts.edu Submitted to: Raonaak Kabir Experiment Performed: xxxx Experiment Due: 10xxxx

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Purpose This lab was performed in order to learn how to measure DC voltages, DC currents, and electrical resistances. The resistance of a wire and the effect of the length of that wire were also studied. Introduction Since DC measurements are the focus of this lab, it would be relevant to touch on what DC means. DC means that the current is constant with respect to time. Therefore, by using a multimeter (complete with ohmmeter, ammeter, voltmeter, and frequency counter) in the ammeter setting, it is possible to find the current that is constantly flowing through the continuous circuit. The multimeter also acts as a voltmeter, finding the difference in voltages between two nodes in a circuit. When calculating voltages, Kirchhoff’s Voltage Law is necessary for both solving for and verifying the voltages that enter and leave a node in a circuit. It says that the sum of the voltages around any closed path will equal zero. This is particularly useful in many of the voltage calculations that are done in common circuitry. The third feature of the multimeter is an ohmmeter. This measures the resistance that is presence around the attached circuit. The resistance can be due to several different types of components attached to the circuit. Some of these are: a thermistor (resistance decreases as temperature increases), a photoresistor (more light decreases resistance), and a potentiometer (turning the knob increases and decreases resistance), and a speaker. Finally, the metal of a wire also has a resistance per length associated with it. The above three quantities—voltage, current, and resistance—can all be related by the fundamental equation known as Ohm’s Law: iR v = where v is voltage in Volts, i is current in Amperes, and R is resistance in Ohms. This simple relationship will be integral to many of the following calculations in the lab. Materials and Equipment DC Power Supply Digital Multimeter Assorted test leads: Banana plug to alligator clip 1 kΩ, ± .5% resistors Thermistor, NCT-102 Potentiometer, 10kΩ Cadmium Sulfide Photocell Small audio speaker 2 Magnet wires, 1 meter length of assorted small gauge wire 2
Procedure A – Measurement of DC Voltage To measure DC voltages, the multimeter needs to be turned to the voltmeter setting (has a v). The red and black wires should then be put into the two jacks labeled COM and VΩHz. The power supply should be connected to next, using the +5V and COMMON jacks. Set the range to 20 and notice that the voltage is 5V. Now measure the voltage across the variable voltage sources: red & black, black & yellow, and red & yellow. Record the voltages. B – Measurement of DC Currents

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## Lab 1 - Tufts University School of Engineering Department...

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