Fall 2012 Midterm 3 Solutions

Immediately after opening the switch what is the rate

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Unformatted text preview: t is the rate (in Joules/s = Watts) at which magnetic energy stored in the inductor, L, is decreasing? 12 V L 2 mH 60 Ω 20 Ω A) B) C) D) E) 1. calculate current in inductor immediately before the switch is opened. 29 W 0W 48 W 7W 15 W This is the current that must go through the two resistors when the switch is opened. Use it to calculate power. Version 1 Page 9 The rate that energy in the inductor decreases is equal to the power dissipated in the two resistors because that is where the energy is going. 16. Current I is charging a circular parallel plate capacitor with plate radius of R. The circulation of the magnetic field, B dl , around a coaxial circular path between the plates with r = R/3 has some definite value. Consider two surfaces bounded by this circular path; the round flat surface (shaded); and the open soup-can (dashed). What can we conclude from the Ampere-Maxwell Law? The total current of all kinds flowing in to the cylinder must be exactly equal to the total current of all kinds flowing out. (this is a paraphrase of the Kirchhoff junction rule). I The cylinder only covers 1/9 of the area of the capacitor plate. This means only 1/9 of the displacement current of the capacitor goes through the shaded side. To make up the difference 8/9 of current must go out the sides in the form of conduction current (remember, the charge has to spread out across the entire plate...). A) The "current" (conduction + displ...
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This document was uploaded on 03/11/2014 for the course PHYSICS 240 at University of Michigan.

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