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Unformatted text preview: Wong, Lemuel – Homework 10 – Due: Apr 4 2007, 5:00 pm – Inst: Matt Mackie 1 This printout should have 17 questions. Multiplechoice questions may continue on the next column or page – find all choices before answering. The due time is Central time. NOTE the unusual due TIME: 5pm central, which is 6pm our time. this is meant to allow more time with the solutions before the exam. 001 (part 1 of 1) 10 points A wire carrying a current 30 A has a length . 1 m between the pole faces of a magnet at an angle 60 ◦ (see the figure). The magnetic field is approximately uniform at 0 . 5 T. We ignore the field beyond the pole pieces. ‘ θ I B What is the force on the wire? Correct answer: 1 . 29904 N. Explanation: Let : I = 30 A , ‘ = 0 . 1 m , θ = 60 ◦ , and B = 0 . 5 T . we use F = I ‘ B sin θ , so F = I ‘ B sin θ = (30 A) (0 . 1 m) (0 . 5 T) sin 60 ◦ = 1 . 29904 N . keywords: 002 (part 1 of 1) 10 points A wire carries a current of 8 A in a direction that make an angle of 31 . 5 ◦ with the direction of the magnetic field of strength 0 . 26 T. Find the magnetic force on a 5 . 79 m length of the wire. Correct answer: 6 . 29256 N. Explanation: Let : B = 0 . 26 T , I = 8 A , ‘ = 5 . 79 m , and θ = 31 . 5 ◦ . The magnetic force is F mag = B I ‘ sin θ = (0 . 26 T)(8 A)(5 . 79 m)(sin31 . 5 ◦ ) = 6 . 29256 N keywords: 003 (part 1 of 1) 10 points A circular loop of radius 3 . 95 cm contains 52 turns of tightly wound wire. If the current in the windings is 0 . 643 A and a constant magnetic field of 0 . 578 T makes an angle of 39 . 9 ◦ with a vector perpendicular with the loop, what torque acts on the loop? Correct answer: 0 . 0607644 N · m. Explanation: Let : r = 3 . 95 cm , N = 52 , I = 0 . 643 A , B = 0 . 578 T , and θ = 39 . 9 ◦ . The torque acting on the loop is: ~ τ = NI ~ A × ~ B Then  ~ τ  = N I  ~ A  ~ B  sin θ = N I πr 2 B sin θ = (52)(0 . 643 A) π (0 . 0395 m) 2 × (0 . 578 T)(sin39 . 9 ◦ ) = . 0607644 N · m Wong, Lemuel – Homework 10 – Due: Apr 4 2007, 5:00 pm – Inst: Matt Mackie 2 keywords: 004 (part 1 of 2) 10 points A circular current loop of radius R is placed in a horizontal plane and maintains a current I . There is a constant magnetic field ~ B in the xyplane, with the angle α ( α < 90 ◦ ) defined with respect to yaxis. The current in the loop flows counterclockwise as seen from above. I z ˆ k x ˆ ı y , ˆ B α If the current in the loop is 0 . 276 A and its radius is 2 . 68 cm, what is the magnitude of the magnetic moment of the loop? Correct answer: 0 . 000622771 A · m 2 ....
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 Spring '08
 Turner
 Physics, Work, Magnetic Field, Correct Answer, WONG, Matt Mackie

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