55 56 lab 3 electric en ergy an d capacitors o ur m

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Unformatted text preview: 70% of the total points achieved) BONUS POINTS FOR TEAMWORK (as specified by course policy) * An "R" in the points column means to rewrite that section only and return it to your lab instructor within two days of the return of the report to you. 55 56 LAB 3: ELECTRIC EN ERGY AN D CAPACITORS O ur m od ern society functions in part becau se w e have learned how to m anipulate electrical energy. Alm ost all of our technology involves electrical energy in one form or another. In this laboratory you w ill investigate the conservation of energy as it relates to electricity. A capacitor is the sim plest d evice that can store electrical energy. The problem s in this lab involve transform ing electrical energy stored in capacitors into light, kinetic energy, and other form s of energy that may be m ore d ifficult to d etect. O BJECTIVES : A fter successfully com pleting this laboratory, you should be able to: A pply the concept of conservation of energy to solve problem s involving electrical phenom ena. D escribe the energy stored in a capacitor based on how it is con nected to other capacitors and to sources of potential d ifferences. PREPARATION : Read Tipler & Mosca: Chapter 6.4; Chapter 25, sections 1-3. Before com ing to lab you should be able to: C alculate the w ork d one by a force exerted on a m oving object. C alculate the relationship betw een pow er and energy. W rite the equation for the energy stored in a single capacitor and und erstand the m eaning of all the quantities involved . 57 LAB 3: ELECTRIC EN ERGY AN D CAPACITORS 58 PROBLEM #1: ELECTRICAL AN D MECHAN ICAL EN ERGY You have a job in a University research group investigating the effect of solar flares on the Earth’s m agnetosphere. Your team is d esigning a sm all, cheap satellite for the investigation. As soon as the satellite achieves a stable orbit, it m ust extend its tw o solar panels. Your team m ust d esign a lightw eight pow er source for d eploying the solar panels. You have been asked to investigate the use of capacitors as a pow er source. You d ecid e to calculate how the m echanical energy transferred to a d evice p ow ered by a capacitor d epend s on the capacitance. You w ill test your calculation u sing a laboratory m od el in w hich a capacitor provid es pow er to a m otor that lifts a m ass. You calculate how far the w eight w ill m ove as a function of the capacitance of the capacitor. You assum e that you know the initial voltage on the capacitor. Instructions: Before lab, read the laboratory in its entirety as well as the required reading in the t extbook. In your lab notebook, respond to the warm up questions and derive a specific prediction for the outcome of the lab. During lab, compare your warm up responses and prediction in your group. Then, work through the exploration, measurement, analysis, and conclusion sections in sequence, keeping a record of your findings in your lab notebook. It is often useful to use Excel to perform data analysis, rather than doing it by hand. Read : Tipler & Mosca Chapter 24.1 & 24.2. Also review Chapter 5.1. EQUIPMEN T You have a m ass set, a rod s and clam ps for securing the m otor w ith sp ool, string, several d ifferent capacitors, a battery or pow er supply, a m eter stick, and a d igital m ultim eter (DMM). Read the section T he Digital M ultimeter (DM M ) in the Equipment a ppend ix. Read the append ices S ignificant Figures , Review of Graphs a nd A ccuracy, Precision and Uncertainty t o help you take d ata effectively. If equipment is missing or broken, submit a problem report by s ending an email to l abhelp@physics.umn.edu . Include the room number and brief description of the p roblem. WARM UP 1. D raw pictures of the situation before the w eight m oves, w hile the w eight is in m otion, and after the w eight has com e to rest. Label all relevant d istances, m asses, forces, and potential d ifferences. Describe the physics principles you need to solve this problem . 2. D efine the initial and final tim es of interest in this problem . Describe (perhaps w ith your d iagram s) w hat happens to energy in the situation betw een those tim es. 59 ELECTRICAL AND MECHANICAL ENERGY – 1302Lab3Prob1 3. A re there objects in the problem w hose potential or kinetic energy is relevant, and that you can calculate d irectly in term s of quantities m easurable in the lab? If so, w rite d ow n expressions for their initial and final (potential or kinetic) energies. 4. U se the w ork-energy theorem to w rite an equation for the net work d one on the w eight. Use this equation and equations from previous steps to w rite the am ount of energy transferred from the capacitor to the w eight, d uring the entire process, as a function of the d istance the w eight m oves. 5. H ow w ould you d efine “efficiency” for this situation? Choose a system . Write an energy conservation equation for your system th at relates the efficiency, the situation’s initial cond itions, and...
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This document was uploaded on 02/23/2014 for the course MANAGMENT 2201 at University of Michigan.

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