TEST03-solutions

TEST03-solutions - Version 003 – TEST03 – tsoi –(56685 1 This print-out should have 16 questions Multiple-choice questions may continue on

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Unformatted text preview: Version 003 – TEST03 – tsoi – (56685) 1 This print-out should have 16 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. 001 10.0 points A magnetic dipole is falling in a conducting metallic tube. Consider the induced current in an imaginary current loop when the magnet is moving away from the upper loop and when the magnet is moving toward the lower loop. N S N pole I above dipole magnet v S pole I below ? ? x y z Determine the directions of the induced currents I above and I below in an imaginary loop shown in the figure, as viewed from above, when the loop is above the falling magnet and when the loop is below the falling magnet. 1. I above = counter-clockwise and I below = counter-clockwise 2. no current flow 3. I above = counter-clockwise and I below = clockwise correct 4. I above = clockwise and I below = counter-clockwise 5. I above = clockwise and I below = clockwise Explanation: When the falling magnet is below the up- per loop,-→ μ ind must be up to attract the falling magnet and slow it down; i.e. , counter- clockwise as viewed from above. Before reaching the lower loop,-→ μ ind must be down to oppose the falling magnet; i.e. , clockwise as viewed from above. N S N pole I above dipole magnet v S pole I below x y z 002 10.0 points An inductor of 230 turns has a radius of 4 cm and a length of 15 cm. The permeability of free space is 1 . 25664 × 10- 6 N / A 2 . Find the energy stored in it when the cur- rent is 0 . 4 A. 1. 0.000222066 2. 7.57362e-05 3. 0.000387561 4. 0.000178211 5. 0.000761369 6. 0.000242613 7. 7.67714e-05 8. 0.000110691 9. 0.0118852 10. 0.000196535 Correct answer: 0 . 000178211 J. Version 003 – TEST03 – tsoi – (56685) 2 Explanation: Let : r = 4 cm = 0 . 04 m , . = 15 cm = 0 . 15 m , N = 230 turns , I = 0 . 4 A , and μ = 1 . 25664 × 10- 6 N / A 2 . The inductance is L = μ N 2 A . = μ N 2 π r 2 . = (1 . 25664 × 10- 6 N / A 2 ) × (230 turns) 2 π (0 . 04 m) 2 . 15 m = 0 . 00222764 H . The energy stored in an inductor is U = 1 2 L I 2 = 1 2 (0 . 00222764 H)(0 . 4 A) 2 = . 000178211 J . 003 10.0 points A total current of 59 mA flows through an infinitely long cylinderical conductor of radius 2 cm which has an infinitely long cylindrical hole through it of diameter r centered at r 2 along the x-axis as shown. x y What is the magnitude of the magnetic field at a distance of 13 cm along the positive x- axis? The permeability of free space is 4 π × 10- 7 T · m / A . Assume the current density is constant throughout the conductor. 1. 1.31624e-07 2. 1.35667e-07 3. 3.48416e-08 4. 9.15825e-08 5. 2.26263e-08 6. 8.82479e-08 7. 7.6202e-08 8. 3.55556e-08 9. 9.44974e-08 10. 5.55556e-08 Correct answer: 8 . 82479 × 10- 8 T....
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This note was uploaded on 11/22/2010 for the course PHY 303L taught by Professor Turner during the Spring '08 term at University of Texas at Austin.

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TEST03-solutions - Version 003 – TEST03 – tsoi –(56685 1 This print-out should have 16 questions Multiple-choice questions may continue on

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