X physics212lecture17slide 28

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Unformatted text preview: 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 dΦ B = Bavo dt Physics 212 Lecture 17, Slide 26 Physics 212 Lecture 17, Slide 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. emf = − y dΦ B dt B b xxxxxxx xxxxxxx xxxxxxx xxxxxxx a v0 x 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 Induced emf produces flux out of screen x Physics 212 Lecture 17, Slide 27 Physics 212 Lecture 17, Slide 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. emf = − y dΦ B dt B b xxxxxxx xxxxxxx xxxxxxx xxxxxxx a v0 x 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: y b a B xxxxxxx v0 I xxxxxxx F = IL × B • Force on top and bottom segments cancel (red arrows) • Force on right segment is directed in –x direction. x Physics 212 Lecture 17, Slide 28 Physics 212 Lecture 17, Slide 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. emf = − y a v0 2 F = 4aBvo R (A) (B) (C) = a 2 B 2vo / R F (D) F = a 2 Bvo R F = IL × B B b xxxxxxx xxxxxxx xxxxxxx xxxxxxx F = IL × B What is the magnitude of the...
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