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Unformatted text preview: irection. y a v0 B b xxxxxxx xxxxxxx xxxxxxx xxxxxxx BB What is the magnitude of the emf induced in the loop just after it enters the field? (A) ε = Babv02 (B) ε = ½ Bav0 (C) ε = ½ Bbv0 (D) ε = Bav0 (E) ε = Bbv0 y a v0 B xxxxxxx b xxxxxxx xxxxxxx xxxxxxx dA a dΦB = Bav0 dt x In a time dt it moves by v0dt Change in Flux = dΦB = BdA = Bav0dt The area in field changes by dA = v0dt a x dΦB emf = dt Calculation A rectangular loop (height = a, length = b, resistance = R, mass = m) coasts with a constant velocity v0 in + x direction as shown. At t =0, the loop enters a region of constant magnetic field B directed in the –z direction. y BB a v0 B b xxxxxxx xxxxxxx xxxxxxx xxxxxxx What is the magnitude of the emf induced in the loop just after it enters the field? (A) ε = Babv02 (B) ε = ½ Bav0 (C) ε = ½ Bbv0 (D) ε = Bav0 (E) ε = Bbv0 y a v0 B xxxxxxx b xxxxxxx a xxxxxxx xxxxxxx In a time dt it moves by v0dt Change in Flux = dΦB = BdA = Bav0dt x The area in field changes by dA = v0dt a dΦB = Bav0 dt x Calculation A rectangular loop (height = a, length = b, resistance = R, mass = m) coasts with a constant velocity v0 in + x direction as shown. At t =0, the loop enters a region of constant magnetic field B directed in the –z direction. y BB a v0 What is the direction of the current induced in the loop just after it enters the field? (A) clockwise (B) counterclockwise (C) no current is induced emf is induced in direction to oppose the change in flux that produced it y a v0 B b xxxxxxx xxxxxxx xxxxxxx xxxxxxx Flux is increasing into the screen x Induced emf produces induced current with flux out of screen dΦB emf = dt B b xxxxxxx xxxxxxx xxxxxxx xxxxxxx x Calculation A rectangular loop (height = a, length = b, resistance = R, mass = m) coasts with a constant velocity v0 in + x direction as shown. At t =0, the loop enters a region of constant magnetic field B directed in the –z direction. y BB a v0 B b xxxxxxx xxxxxxx xxxxxxx xxxxxxx What is the direction of the net force on the loop just after it enters the field? (A) +y (B) ­y (C) +x (D) ­x Force on a current in a magnetic field: r rr F = IL × B y b a B xxxxxxx v0 I xxxxxxx • Force on top and bottom segments cancel (red arrows) • Force on right segment is directed in –x direction. x dΦB emf = dt x Calculation A rectangular loop (height = a, length = b, resistance = R, mass = m) coasts with a constant velocity v0 in + x direction as shown. At t =0, the loop enters a region of constant magnetic field B directed in the –z direction. y a BB v0 B b xxxxxxx xxxxxxx xxxxxxx xxxxxxx r rr F = IL × B What is the magnitude of the net force on the loop just after it enters the field? F = a 2 Bv0 R F (D) B F = 4aBv0 R (A) (B) (C) = a 2 2v0 2 / R dΦB emf = dt x ε = Bav0 F = a 2 B 2v0 / R rr F =...
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This document was uploaded on 02/13/2014.

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