Will the acceleration a of the falling ring in the

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Unformatted text preview: 212 Lecture 17, Slide 19 Physics 212 Lecture 17, Slide Faraday’s Law: dΦ B emf = ∫ E ⋅ d = − dt where Φ B ≡ ∫ B ⋅ dA In Practical Words: 1) When the flux ΦB through a loop changes, an emf is induced in the loop. through a loop changes, an 2) The emf will make a current flow if it can (like a battery). 3) The current that flows induces a new magnetic field. 4) The new magnetic field opposes the change in the original magnetic field that created it. (Lenz’ Law) B Demo dB/dt Physics 212 Lecture 17, Slide 20 Physics 212 Lecture 17, Slide Faraday’s Law: dΦ B emf = ∫ E ⋅ d = − dt where Φ B ≡ ∫ B ⋅ dA Executive Summary: emf→current→field a) induced only when flux is changing only flux b) opposes the change opposes Physics 212 Lecture 17, Slide 21 Physics 212 Lecture 17, Slide Checkpoint 2 A horizontal copper ring is dropped from rest directly above the north pole of a permanent magnet (copper is not ferromagnetic) “Please do not display this in lecture but that picture on this checkpoint with the falling conducting loop looked a LOT McDonalds like french fries.” Will the acceleration a of the falling ring in the presence of the magnet be any different than it would have been under the influence of just gravity (i.e. g)? A. a > g B. a = g C. a < g “THe induced emf will try to resist the increasing magnetic field from the THe magnet so it will produce a magnetic field opposite to that and fall faster. ” “The force by the B field will always be horizontal and will not affect the vertical The force on the ring.” force “Some of the gravitational potential energy gets dissipated as heat AS the Some Physics 212 Lecture 17, Slide 22 Physics 212 Lecture 17, Slide loop is falling” loop Checkpoint 2 A horizontal copper ring is dropped from rest directly above the north pole of a permanent magnet F O X B B (copper is not ferromagnetic) Will the acceleration a of the falling ring in the presence of the magnet be any different than it would have been under th...
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This note was uploaded on 04/14/2013 for the course PHYS 212 taught by Professor Selen during the Spring '08 term at University of Illinois at Urbana–Champaign.

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