V.Magnetic Circuits Contour of integration of Ampere's law D Ho N turns H=5 Flux leaving Closed surface S has zero net flux through it Flux entering S L Current i passes perpendicularly through contour Ntimes Faraday's law evaluated for dashed contour following N turn coil in the direction of the current Figure 6-8 The magnetic field is zero within an infinitely permeable magnetic core and is constant in the air gap if we neglect fringing.The flux through the air gap is constant at every cross section of the magnetic circuit and links the N turn coil N times. In iron core: H=0 limB=ui三 1山0 B finite ∮H.di=Hs=Ni→H=NI Φ=oHDd=to Dd N ∮B.da=0 天=Nw=bgD0N1L=子=gD心 s 6.641,Electromagnetic Fields,Forces,and Motion Lecture 8 Prof.Markus Zahn Page 9 of 136.641, Electromagnetic Fields, Forces, and Motion Lecture 8 Prof. Markus Zahn Page 9 of 13 V. Magnetic Circuits In iron core: H=0 lim B = H µ→∞ µ ⇒ B finite v∫ i ⇒ Ni H dl = Hs = Ni H = s µ Φ µ 0 0 Dd N = H Dd = s i S B da = 0 ∫ i v µ µ λ λΦ ⇒ 0 0 Dd 2 2 Dd =N = N i L= = N s i s