online assignment 4-7-1

online assignment 4-7-1 - MasteringPhysics Assignment Print...

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Manage this Assignment: 7. Induction Part 2 Due: 11:00pm on Thursday, February 25, 2010 Note: To understand how points are awarded, read your instructor's Grading Policy . Print Version with Answers Energy Stored in an Inductor Description: Numerical calculation of the inductance necessary to store a given amount of energy. The electric-power industry is interested in finding a way to store electric energy during times of low demand for use during peak-demand times. One way of achieving this goal is to use large inductors. Part A What inductance would be needed to store energy (kilowatt-hours) in a coil carrying current ? This is probably not the best way to store energy: unless the coil is a superconductor, the amount of heat dissipated in the coil would be enormous. At this point, there is no way to produce large superconducting coils. Think of this problem as a practice exercise rather than a realistic example. Hint A.1 The formula for the energy stored in a current-carrying inductor Recall the formula for energy stored in an inductor: . Hint A.2 Express the energy in joules What is the energy expressed in joules? Express your answer numerically, to three significant figures. ANSWER: = joules ANSWER: = H RL Circuit Phasor Drawings Applet Vector Description: For an RL circuit, given the current phasor, draw the resistor, inductor, and total voltage phasors. (vector applet) An RL circuit is driven by an AC voltage source as shown in the figure. Page 1 of 11 MasteringPhysics: Assignment Print View 2/23/2010 http://session.masteringphysics.com/myct/assignmentPrint?assignmentID=1355241
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On the phasor diagram below, draw the phasor that represents the voltage across the resistor ( ) at the instant indicated. The orientation of your vectors will be graded. The exact length of your vectors will not be graded but the relative length of one to the other will be graded. Hint A.1 How to approach the problem By Ohm’s law, the voltage across the resistor is directly proportional to the current in the circuit. There is no phase difference between the current and the resistor voltage. ANSWER: View Part B The inductive reactance of the circuit is exactly twice the resistance: . Draw the phasor that represents the voltage across the inductor ( ) at the instant indicated. The orientation of your vectors will be graded. The exact length of your vectors will be graded. Hint B.1 How to approach the problem In a series RL circuit, the phasor representing the voltage across the inductor always leads the current by 90 degrees. Hint B.2 Phasor length The length of a phasor represents peak voltage or current. Recall that the inductive reactance is the "effective" resistance across the inductor, and relates the peak voltage and current across the inductor by a relationship analogous to Ohm's law: . ANSWER:
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This note was uploaded on 07/01/2010 for the course PHYS 101213 taught by Professor Bratton during the Spring '10 term at CSU Chico.

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online assignment 4-7-1 - MasteringPhysics Assignment Print...

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