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Unformatted text preview: 1 February 22, 2008 Physics 132-Winter 2008 Prof. Jim Beatty-Ohio State 1 Physics 132 Introductory Physics: Electricity and Magnetism Winter Quarter 2008 Lecture 20 February 22, 2008 Physics 132-Winter 2008 Prof. Jim Beatty-Ohio State 2 Combining Electric and Magnetic Fields x y z Electric Field gives F E =qE Magnetic Field gives F B =qv B Can we construct a combination of v, B and E to give uniform linear motion? Yes! v, E, and B all perpendicular. Try v along +x, B along -y, and E along +z. v is in E B direction. F E = q E = qE z F B = q v B = qvB ( x y ) = qvB ( z ) F tot = F E + F B = q ( E vB ) z F tot =0 if E=vB. This is a velocity selector! Only v=E/B goes straight. + B v E 2 February 22, 2008 Physics 132-Winter 2008 Prof. Jim Beatty-Ohio State 3 The Hall Effect x y z B = B z Electrons moving along a conductor feel a magnetic force that pushes them toward the side. This creates induced charge, and an electric field which cancels out the magnetic force for electrons at the drift velocity. (d=width, A=area) v d = E B = V Hall dB v d = J ne = i neA n = Bi eV Hall d A We get the number of (and sign) of charge carriers! i i- i i-- - - - - - - - - - + + + + + + + + + + v d February 22, 2008 Physics 132-Winter 2008 Prof. Jim Beatty-Ohio State 4 Force on a Current-Carrying Wire F = q v B dq v = dq d x dt = d x dq dt = i d x q v = i L F = i L B For moving point charges: How do we deal with moving charges forming currents on a wire?...
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- Winter '08