Physics 212 Lecture 15 Amperes Law Physics 212

Physics 212 Lecture 15 Ampere’s Law Physics 212 Lecture 15, Slide 1

Main Point We used our knowledge of the magnetic field produced by a long straight currentcarrying wire to develop an understanding of Ampere’s law, that the integral of B dot dl around any closed path is equal to m 0 times the current enclosed by that path. Ampere’s law can be used to determine the magnetic field produced by sufficiently symmetric current distributions. In particular, we used Ampere’s law to calculate the magnetic field produced by the cylindrically-symmetric infinite straight current -carrying wire and the planar-symmetric infinite sheet of current. Physics 212 Lecture 15, Slide 2

Practice on Enclosed Currents Checkpoint 1 a For which loop is B·dl the greatest? A. Case 1 B. Case 2 C. Same : 08 Checkpoint 1 b For which loop is B·dl the greatest? A. Case 1 B. Case 2 C. Same Checkpoint 1 c For which loop is B·dl the greatest? A. Case 1 B. Case 2 C. Same Physics 212 Lecture 15, Slide 3

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An infinitely long hollow conducting tube carries current I in the direction shown. Checkpoint 2 a What is the direction of the magnetic field inside the tube? A. clockwise B. counterclockwise C. radially inward to the center D. radially outward from the center E. the magnetic field is zero : 22 Physics 212 Lecture 15, Slide 5

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Checkpoint 2 b : 22 Physics 212 Lecture 15, Slide 7

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Ampere’s Law I into screen : 12 Physics 212 Lecture 15, Slide 9

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CD Which of the following current distributions would give rise to the B. d. L distribution at the right. A B C Physics 212 Lecture 15, Slide 11

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Match the other two: CD A B Physics 212 Lecture 15, Slide 14

Solenoid Several loops packed tightly together form a uniform magnetic field inside, and nearly zero magnetic field outside. Physics 212 Lecture 15, Slide 15

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Example Problem An infinitely long cylindrical shell with inner radius a and outer radius b carries a uniformly distributed current I out of the screen. y a Sketch |B| as a function of r. Conceptual Analysis I x b Strategic Analysis Physics 212 Lecture 15, Slide 17

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