HW _12 P2213 F09

# HW _12 P2213 F09 - the magnetic force acting on the rod in...

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1 Physics 2213 Homework #12 Fall 2009 Due : Do not hand in. However, the quiz during the last week of class (after Thanksgiving) will include this homework. Read: Chapter 29: 29.1 – 29.7. Please understand how the DC motor works. Exercises and Problems (6 problems) : (1) Check the units of the terms in the Maxwell equations to show they are correct. How many basic parameters (in free space) are there ? How do the Maxwell equations look like if there are no electric charges/current present ? Now, how many basic parameters (in free space) are there ? (2) #29.18 [Two Windings] (3) #29.25 [Sliding Rod Circuit] Please add: (e) Suppose the external force pushing the rod to the right is suddenly removed at time t = 0 when the rod's speed is v o . The magnetic force acting on the induced electric current in the rod will then gradually slow the rod down until it comes to rest. Write an algebraic expression for
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Unformatted text preview: the magnetic force acting on the rod in terms of its subsequent speed v, and use this to derive a mathematical expression for the rod's subsequent speed v(t) as a function of time t in terms of m, H, R, B, and v o . (f) Show that your algebraic result for v(t) is physically reasonable and has the correct units. (g) Use your result for v(t) to show that after the external force is removed, the total distance the rod subsequently moves = mv o R/B 2 H 2 . [HINTS: Rememberâ€”as the rod slows down, the current decreases, and so does the magnetic force. To find v(t), you'll need to derive and solve a simple differential equation like one we used in RC circuits.] (4) #29.30 [Induced E Field] (5) #29.52 [Make a Generator] Please add: (c) Draw a graph of the emf in the loop as a function of time t, and label both axes with numerical values. (6) #29.65 [Motional emf]...
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## This note was uploaded on 12/25/2009 for the course PHYS 213 at Cornell.

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