ism_chapter_28 - Chapter 28 Magnetic Induction Conceptual...

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625 Chapter 28 Magnetic Induction Conceptual Problems *1 Determine the Concept We know that the magnetic flux (in this case the magnetic field because the area of the conducting loop is constant and its orientation is fixed) must be changing so the only issues are whether the field is increasing or decreasing and in which direction. Because the direction of the magnetic field associated with the clockwise current is into the page, the changing field that is responsible for it must be either increasing out of the page (not included in the list of possible answers) or a decreasing field directed into the page. correct. is ) ( d 2 Determine the Concept Note that when R is constant, B in the loop to the right points out of the paper. ( a ) If R increases, I decreases and so does B . By Lenz’s law, the induced current is counterclockwise. ( b ) If R decreases, the induced current is clockwise. 3 •• Determine the Concept If the counterclockwise current in loop A increases, so does the magnetic flux through B. To oppose this increase in flux, the induced current in loop B will by clockwise. If the counterclockwise current in loop A decreases, so does the magnetic flux through B. To oppose this decrease in flux, the induced current in loop B will be counterclockwise. We can use B F r l r r × = I to determine the direction of the forces on each loop and, hence, whether they will attract or repel each other. ( a ) If the current in B is clockwise the loops repel one another. ( b ) If the current in B is counterclockwise the loops attract one another. 4 •• Determine the Concept We know that, as the magnet moves to the right, the flux through the loop first increases until the magnet is half way through the loop and then decreases. Because the flux first increases and then decreases, the current will change directions, having its maximum values when the flux is changing most rapidly. ( a ) and ( b ) The following graph shows the flux and the induced current as a function of
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Chapter 28 626 time as the bar magnet passes through the coil. When the center of the magnet passes through the plane of the coil d φ m / dt = 0 and the current is zero. -1.0 -0.8 -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0 - 3 - 2 - 10123 time (arbitrary units) Flux Current 5 •• Determine the Concept Because the magnet moves with simple harmonic motion, the flux and the induced current will vary sinusoidally. The current will be a maximum wherever the flux is changing most rapidly and will be zero wherever the flux is momentarily constant. ( a ), ( b ) The following graph shows the flux, m , and the induced current (proportional to d m / dt ) in the loop as a function of time. -1.0 -0.8 -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0 -5 0 5 10 15 time (arbitrary units) Flux Current
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Magnetic Induction 627 *6 Determine the Concept The magnetic energy stored in an inductor is given by 2 2 1 m LI U = . Doubling I quadruples U m .
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This homework help was uploaded on 02/26/2008 for the course PHYSICS 11 taught by Professor Licini during the Spring '07 term at Lehigh University .

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ism_chapter_28 - Chapter 28 Magnetic Induction Conceptual...

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