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Unformatted text preview: Version 086 EX2 ditmire (58335) 1 This printout should have 23 questions. Multiplechoice questions may continue on the next column or page find all choices before answering. 001 10.0 points The current in a resistor decreases by 3 . 5 A when the voltage applied across the resistor decreases from 15 . 9 V to 5 . 29 V. Find the resistance of the resistor. 1. 4.15917 2. 3.03143 3. 2.97519 4. 1.84091 5. 4.48551 6. 2.30201 7. 8.60588 8. 2.77591 9. 4.6943 10. 2.44527 Correct answer: 3 . 03143 . Explanation: Let : I = 3 . 5 A , V i = 15 . 9 V , and V f = 5 . 29 V . V = I R Call the initial voltage and current V i and I , respectively, and the final voltage and current V f and ( I I ), respectively. R = V I = V i I = V f I I V i ( I I ) = V f I ( V i V f ) I = V i I V i I = V i V f I , so R = V i I = V i V f I = 15 . 9 V 5 . 29 V 3 . 5 A = 3 . 03143 . 002 10.0 points The figure below shows a cylindrical coaxial cable of radii a , b , and c in which equal, uni formly distributed, but antiparallel currents i exist in the two conductors. O i out i in F E D C r 1 r 2 r 3 r 4 c b a Which expression gives the magnitude B ( r 3 ) at D of the magnetic field in the re gion b < r 3 < a ? 1. B ( r 3 ) = i ( a 2 b 2 ) 2 r 3 ( r 2 3 b 2 ) 2. B ( r 3 ) = i ( r 2 3 b 2 ) 2 r 3 ( a 2 b 2 ) 3. B ( r 3 ) = ir 3 2 a 2 4. B ( r 3 ) = i ( a 2 r 2 3 ) 2 r 3 ( a 2 b 2 ) correct 5. B ( r 3 ) = i ( a 2 + r 2 3 2 b 2 ) 2 r 3 ( a 2 b 2 ) 6. B ( r 3 ) = ir 3 2 b 2 7. B ( r 3 ) = i 2 r 3 8. B ( r 3 ) = i r 3 9. B ( r 3 ) = 0 10. B ( r 3 ) = ir 3 2 c 2 Explanation: Amperes Law states that the line inte gral contintegraldisplay vector B d vector around any closed path equals Version 086 EX2 ditmire (58335) 2 I , where I is the total steady current pass ing through any surface bounded by the closed path. Considering the symmetry of this problem, we choose a circular path, so Amperes Law simplifies to B (2 r 3 ) = I en , where r 3 is the radius of the circle and I en is the current enclosed. Since A en A cylinder = ( r 2 3 b 2 ) ( a 2 b 2 ) , when b < r 3 < a for the cylinder, B = I en 2 r 3 = bracketleftbigg i i ( r 2 3 b 2 ) ( a 2 b 2 ) bracketrightbigg 2 r 3 = i parenleftbigg a 2 r 2 3 a 2 b 2 parenrightbigg 2 r 3 = i ( a 2 r 2 3 ) 2 r 3 ( a 2 b 2 ) . 003 10.0 points A conductor consists of an infinite number of adjacent wires, each infinitely long and carrying a current I (whose direction is outof thepage), thus forming a conducting plane....
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 Spring '10
 Avram
 Physics, Current

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