PHYS 0175 1st Edition Lecture 26Outline of Last Lecture II. Torque in current carrying wireII. Gauss’ Law for Magnetic fieldsIII. Ampere’s LawIV. Cylindrical symmetryV. 2 long straight wiresCurrent LectureIII. magnetic fluxVI. Faraday’s law of inductionVII. Direction of induced emfVIII.Lenz’s lawIX. recapitulationX. moving copper ringCurrent LectureIV. magnetic fluxa. not a closed surface-else would be zeroi. by gauss’ lawb. counts # magnetic field lines through surfacec. only || component contributes because of dot productXI. Faraday’s law of inductiona. Emf=-d(magnetic flux)/dtb. No induced emf if constant magnetic fluxXII. Direction of induced emfa. Oriented “vector area”b. Sign magnetic fluxc. Sign of induced emp causes current to flowd. Will go against d(magnetic flux)/dt(always – oppose)e. “negative feedback” stabilizeXIII. Lenz’s lawa. Direction of magnetic induction effect is such as to oppose the cause of the effectXIV.Recapitulationa. 2 ways to change magnetic fluxi. magnitude of magnetic fieldii. size or orientationb. emf=-N*d(flux)/dti. N=# turns on wireii. Emf=RI=V (if ohmic material-conductor)iii. Current induced will oppose change in B^ externalXV. moving copper ringa. no current outside bielfb. constant induced current insidec. just entering and just exiting, will have induced currents of opposite
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