26 Maxwell - Craig Ogilvie Craig Ogilvie 11 Course stuff §...

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Unformatted text preview: Craig Ogilvie Craig Ogilvie 11 Course stuff § Welcome back! § 2nd mid-term exam Wed 30 March – Can bring two 4” by 6” cards for the 2nd exam Craig Ogilvie Craig Ogilvie 22 Summary of Lecture 25 § Circuits with R and L – induced emf opposes change when current changes – currents take time to build to their final value – time constant τ = L/R governs the build up of the current § Inductors store energy – U = 1/2*L*I2 – energy can be released for use » spark plugs ) 1 ( ) ( τ ε t e R t i-- = i Craig Ogilvie Craig Ogilvie 33 Goals For Today § Energy is stored in B-field ! § Previous work on Faraday’s Law – changing B-field induces an E-field § This week – changing E-field induces a B-field Craig Ogilvie Craig Ogilvie 44 How/Where is the Energy Stored? As an example, consider a long solenoid l A N L LI U 2 2 2 1 μ = = B u volume U = 2 2 1 B u B μ = Pre-lecture video Craig Ogilvie Craig Ogilvie 55 Energy Stored in B-field § Energy stored in inductor as a B-field § It costs energy to set up a B-field – energy density of B-field (general result) 2 2 1 B u B μ = § Recall from earlier in semester § it also takes energy to set up E-field – energy density of E-field (general result) 2 2 1 E u E ε = Craig Ogilvie...
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This note was uploaded on 09/20/2011 for the course PHYS 222 taught by Professor Johnson during the Spring '07 term at Iowa State.

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26 Maxwell - Craig Ogilvie Craig Ogilvie 11 Course stuff §...

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