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Unformatted text preview: Solution for Homework 18 Inductance Solution to Homework Problem 18.1(What Makes Second Speaker Work?) Problem: In lab, the second speaker we built was made with a fixed magnet and a coil attached to a vibrating board. What physical law in most important in describing the operation of this speaker? Select One of the Following: (a) Faraday’s Law. (b) Ampere’s Law (cAnswer) The Lorentz Force (d) BiotSavart Law (e) Coulomb’s Law Solution Lorentz Force Total Points for Problem: 3 Points Solution to Homework Problem 18.2(Gauss Gun Energy) Problem: I estimate that the Gauss gun (a solenoid) is wound with 500 turns over a distance of 15cm with an average radius of 1 . 5cm . The peak current is about 300A . Calculate the energy stored in the Gauss’ gun at peak current. Use the infinite solenoid approximation. Select One of the Following: (aAnswer) 70J (b) . 01J (c) 200J (d) 6000J (e) . 3J Solution The energy stored in a magnetic field is given by U = 1 2 LI 2 where L is the selfinductance. The selfinductance of a solenoid, in the infinite solenoid approximation is, L = μ n 2 Aℓ . For the Gauss gun the turns per unit length is n = N/L = (500) / (0 . 15m) = 3333m 1 , and the self inductance is (4 π × 10 7 Tm A )(3333m 1 ) 2 π (1 . 5cm) 2 (0 . 15m) = 0 . 00148H and the total energy stored in the field U = 1 2 LI 2 = 1 2 (0 . 00148H)(300A) 2 = 70J Total Points for Problem: 3 Points 1 Solution to Homework Problem 18.3(Voltage Across Commerical Inductor) Problem: Coilcraft makes a chip mount inductor with inductance 10 μ H and peak current 1 . 4A . If we power this inductor at its peak current with a signal that has the frequency of house current, the inductor carries a current of I ( t ) = 1 . 4A sin ω t where ω = 380s 1 Compute the peak voltage across the inductor....
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This note was uploaded on 05/04/2008 for the course PHYS 2074 taught by Professor Stewart during the Winter '08 term at Arkansas.
 Winter '08
 Stewart
 Inductance, Work

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