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Lec18-1

# Lec18-1 - ture 18-1 ture Faradays Law of Induction The...

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cture 18- cture 18- 1 Faraday’s Law of Induction The magnitude of the induced EMF in conducting loop is equal to the rate at which the magnetic flux through the surface spanned by the loop changes with time. where \$ B S B ndA Φ = ur g Minus sign indicates the sense of EMF: Lenz’s Law Decide on which way n goes Fixes sign of ϕ B RHR determines the positive direction for EMF N N r E nc g d v s Ñ = - δΦ Β δτ

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cture 18- cture 18- 2 Motional EMF of Sliding Conductor Lenz’s Law gives direction Induced EMF: counter-clockwise Faraday’s Law B d dx Bl Blv dt dt ε Φ = - = - = - This EMF induces current I Blv I R R = = - Magnetic force F M acts on this I 2 2 M B l v F I lB R = = F M decelerates the bar 2 2 dv B l v m dt R = - 2 2 dv B l dt v mR = - ( 29 2 2 ( ) 0 B l t mR v t v e - ÷ ÷ =
cture 18- cture 18- 3 Ways to Change Magnetic Flux Changing the magnitude of the field within a conducting loop (or coil). Changing the area of the loop (or coil) that lies within the magnetic field. Changing the relative orientation of the field and the loop . motor generator cos B BA θ Φ = http://www.wvic.com/how-gen-works.htm

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cture 18- cture 18- 4 Other Examples of Induction Switch has been open for some time: Nothing happening Switch is just closed: EMF induced in Coil 2 + - Switch is just opened: EMF is induced again + - Switch is just closed: EMF is induced in coil + - Back emf (counter emf)
cture 18- 5 Eddy Currents The presence of eddy current in the object results in dissipation of electric energy that is derived from mechanical motion of the object. The dissipation of electric energy in turn causes the loss of mechanical energy of the object, i.e., the presence of the field damps motion of the object. A current induced in a solid conducting

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Lec18-1 - ture 18-1 ture Faradays Law of Induction The...

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