# Whatisthedirectionandthemagnitudeoftheforceontheloop

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Unformatted text preview: e influence of just gravity (i.e. g)? A. a > g B. a = g C. a < g Like poles repel Ftotal < mg a < g This one is hard ! B field increases upward as loop falls Clockwise current (viewed from top) is induced Physics 212 Lecture 17, Slide 23 Physics 212 Lecture 17, Slide Checkpoint 2 A horizontal copper ring is dropped from rest directly above the north pole of a permanent magnet HO W IT WO R KS Looking down B (c o p p e r is no t fe rro m a g ne tic ) 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 T h is o ne is h a rd ! B fie ld inc re a s e s up wa rd a s lo o p fa lls C lo c kwis e c urre nt (vie we d fro m to p ) is ind uc e d Main Field produces horizontal forces “Fringe” Field produces vertical force I I B IL X B points UP Ftotal < mg a < g Demo ! dropping magnets e-m cannon Physics 212 Lecture 17, Slide 24 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. What is the direction and the magnitude of the force on the loop when half of it is in the field? y a v0 B b xxxxxxx xxxxxxx xxxxxxx xxxxxxx x • Conceptual Analysis – – Once loop enters B field region, flux will be changing in time Faraday’s Law then says emf will be induced • Strategic Analysis – – – Find the emf Find the current in the loop Find the force on the current Physics 212 Lecture 17, Slide 25 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 = − dΦ B dt y a v0 B b xxxxxxx xxxxxxx xxxxxxx xxxxxxx What is the magnitude of the emf induced in the loop just after it enters the...
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