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Unformatted text preview: Kapoor (mk9499) – oldhomework 20 – Turner – (60230) 1 This printout should have 9 questions. Multiplechoice questions may continue on the next column or page – find all choices before answering. 001 (part 1 of 2) 10.0 points A circular coil of 255 turns and area 0 . 11 m 2 is in a uniform magnetic field of 0 . 58 T. The maximum torque exerted on the coil by the field is 0 . 0012 N · m. Calculate the current in the coil. Correct answer: 7 . 37599 × 10 − 5 A. Explanation: Let : τ = 0 . 0012 N · m , N = 255 , A = 0 . 11 m 2 , and B = 0 . 58 T . The maximum torque is τ = N I A B , so the current in the coil is I = τ N A B = (0 . 0012 N · m) (255) (0 . 11 m 2 ) (0 . 58 T) = 7 . 37599 × 10 − 5 A . 002 (part 2 of 2) 10.0 points Assume the 255 turns of wire are used to form a singleturn coil with the same shape but much larger area. What is the current if the maximum torque exerted on the coil by the field is 0 . 0012 N · m? Correct answer: 2 . 89255 × 10 − 7 A. Explanation: Let : N = 255 . The radius of the coil is r = radicalbigg A π . and the total length of the coil is C = N 2 π r . The new radius of the singleturn coil is R = C 2 π = N r , so the new area of the coil is A new = π R 2 = N 2 A . Using the equation for the current, we find the new value of the current: I new = τ N 2 A B = I N = 7 . 37599 × 10 − 5 A 255 = 2 . 89255 × 10 − 7 A . 003 10.0 points A circular loop of radius 3 . 12 cm contains 54 turns of tightly wound wire. If the current in the windings is 0 . 668 A and a constant magnetic field of 0 . 408 T makes an angle of 28 . 2 ◦ with a vector perpendicular with the loop, what torque acts on the loop? Correct answer: 0 . 0212686 N · m. Explanation: Let : r = 3 . 12 cm , N = 54 , I = 0 . 668 A , B = 0 . 408 T , and θ = 28 . 2 ◦ . The torque acting on the loop is: vector τ = NI vector A × vector B Then  vector τ  = N I  vector A  vector B  sin θ = N I πr 2 B sin θ = (54)(0 . 668 A) π (0 . 0312 m) 2 × (0 . 408 T)(sin28 . 2 ◦ ) = . 0212686 N · m Kapoor (mk9499) – oldhomework 20 – Turner – (60230)...
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 Fall '08
 Turner
 Physics, Work, Magnetic Field, Kapoor, long straight wire

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