# Changes direction twice per second the current would

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Unformatted text preview: g in time. The current induced in the loop is: A. zero B. clockwise C. counterclockwise • Motional emf is ZERO • There is no motion of conduction electrons ! X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X Clockwise restores B • HOWEVER: The flux IS changing • B decreases in time • current induced to oppose the flux change • clockwise current puts back B that was removed THIS IS NEW !! Faraday’s Law explains existence of emf when the motional emf is ZERO! Physics 212 Lecture 17, Slide 15 Physics 212 Lecture 17, Slide Checkpoint 1c Now suppose that the loop is spun around a vertical axis as shown, and that it makes one complete revolution every second. The current induced in the loop: A. Is zero B. Changes direction once per second C. Changes direction twice per second “the current would be zero since the flux would cancel out. ” “The current experiences sinusoidal change, so in one period (second), the The current will change directions once.” current “It goes from increasing field lines through the loop to decreasing field lines It through the loop twice per rotation” through Physics 212 Lecture 17, Slide 16 Physics 212 Lecture 17, Slide Checkpoint 1c Now suppose that the loop is spun around a vertical axis as shown, and that it makes one complete revolution every second. The current induced in the loop: A. Is zero B. Changes direction once per second C. Changes direction twice per second Current changes direction every time the loop becomes perpendicular with the B field emf ~ dΦ/dt (B dA = max) d/dt (B dA ) = 0 O X B dA O B X dA Physics 212 Lecture 17, Slide 17 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 generates a new magnetic field. I Physics 212 Lecture 17, Slide 18 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 dB/dt Physics...
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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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