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Unformatted text preview: Physics 21 Fall, 2004 Solution to HW15 29 P 21 Determine the magnetic ux through a square loop of side a if one side is parallel to, and a distance a from, a straight wire that carries a current I . The field of the wire is B ( r ) = I/ 2 r , directed perpen dicular to the loop. The ux is = Z 2 a a B ( r ) a dr = I 2 a Z 2 a a dr r The definite integral is Z 2 a a dr r = ln r  2 a a = ln 2 a ln a = ln 2 a a = ln 2 Combining terms, we obtain = Ia 2 ln 2 . 6931 Ia 2 . One can get a pretty good approximate answer by assuming B ( r ) is constant over the loop and taking the value at the middle, where r = 1 . 5 a . Then = B (1 . 5 a ) a 2 = I 2 (1 . 5 a ) a 2 = 2 3 Ia 2 . 6667 Ia 2 . 29 P 40 Neon signs require 12 kV for their operation. To operate from a 220 V line, what must be the ratio of sec ondary to primary turns of the transformer? What would be the voltage output if the transformer were connected back ward?...
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This note was uploaded on 08/06/2008 for the course PHYS 21 taught by Professor Hickman during the Fall '07 term at Lehigh University .
 Fall '07
 Hickman
 Physics, Current

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