p2f10_lec05_inductance_displacement_current_oscillations

# p2f10_lec05_inductance_displacement_current_oscillations -...

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1 Physics 1200 Lecture 05 Inductance Displacement Current Harmonic oscillations

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2 Summary of magnetic effects A changing magnetic field induces an electric field. A changing magnetic flux induces a current that opposes the change. The induced current creates a magnetic field. In a superconductor, the field and current last forever. In a normal conductor, the induced current and field decay due to resistance.
3 Inductance When we pass current through any device, a magnetic field results, some of which is enclosed by the current path in the device. l B r , B B L Li Φ Φ = The total flux through the current path is . It can be related to the current by a constant: that we will call inductance, 2 0 For a solenoid: L n lA μ = Units: Henry volt-second 1 henry=1 amp Fall 2009

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4 Self inductance B d di Li L dt dt d di Emf L dt dt Φ Φ = = Φ = - = - B B When the current through an inductor changes, the magnetic flux changes too. which results in an emf in the circuit: A real consequence: When we attempt to switch off the current in an inductor, a back potential is generated that can be large if the current is switched off too quickly.
5 Energy storage in an inductor 2 0 2 2 2 2 0 0 0 1 2 1 1 2 2 The energy stored in an inductor can be calculated: For a solenoid ( ) , we can show that: B B B di V L dt di P Vi Li dt U Pdt Lidi Li B ni U n lAi B lA u B μ = = = = = = = = = =

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6 Energy density In terms of the fields produced, the energy density is, 2 0 2 1 B u B μ = 2 0 2 E u E ε = For electric fields For magnetic fields
7 Inductors in circuits

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p2f10_lec05_inductance_displacement_current_oscillations -...

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