Chapter 27 Electromagnetic Induction and faraday's law the direction of emf(感应电动势的方向) dg dt 4-2 means the induced emf tends to oppose the flux B change 1)规定回路的绕行正方向。 2)规定当回路中磁力线的方向 和所规定的回路的绕行正方向成 右手螺旋关系 1>0①>0
Chapter 27 Electromagnetic Induction and Faraday’s Law “-” means the induced emf tends to oppose the flux change. the direction of emf (感应电动势的方向) t Φ d d = − N B L 0 1）规定回路的绕行正方向。 2）规定当回路中磁力线的方向 和所规定的回路的绕行正方向成 右手螺旋关系. Φ 0
Chapter 27 Electromagnetic Induction and faraday's law 当磁力线方向与计算方向成右手螺旋关系时 磁通量的值取正,否则磁通量的值取负 3)计算结果的正负给出了电动势的方向; e>0:说明电动势的方向就是所设的计算方向; <0:说明电动势的方向与所设计算方向相反
Chapter 27 Electromagnetic Induction and Faraday’s Law 当磁力线方向与计算方向成右手螺旋关系时 磁通量的值取正，否则磁通量的值取负； 3) 计算结果的正负给出了电动势的方向； 0 : 说明电动势的方向就是所设的计算方向； 0 : 说明电动势的方向与所设计算方向相反
Chapter 27 Electromagnetic Induction and faraday's law ◆ magnetic flux linkage(磁通链) If the loop is replaced by a closely packed coil ofn turns, the induced emfis dp B dt dt Where: Y=Nap Called magnetic flux linkage(磁通链)
Chapter 27 Electromagnetic Induction and Faraday’s Law If the loop is replaced by a closely packed coil of N turns， the induced emf is： t t N B d dψ d d = = − Where： ψ = N Called magnetic flux linkage（磁通链）. magnetic flux linkage（磁通链）
Chapter 27 Electromagnetic Induction and Faradays Law o the method to change magnetic flux p631-634 Φn=|B.dA=|Bcos.d 1) Change the magnitude of B within the coil 2) Change the area of the coil, or the portion of the area that happens to lie within the magnetic field 3)Change the angle between the direction of B and the area of coill
Chapter 27 Electromagnetic Induction and Faraday’s Law B = BdA = Bcos dA the method to change magnetic flux p631-634 1） Change the magnitude of within the coil. 2）Change the area of the coil， or the portion of the area that happens to lie within the magnetic field. 3）Change the angle between the direction of and the area of coil. B B
Chapter 27 Electromagnetic Induction and faraday's law 3. Lenz's law An induced emf is always in a direction that opposes the original change in flux that caused it. 楞次定律闭合的导线回路中所出现的感应电流 总是使它自己所激发的磁场反抗任何引发电磁感应的 原因. discussion 1)Lenz's law is consistent with the law of conservation of energy. 楞次定律是能量守恒定律的一种表现
Chapter 27 Electromagnetic Induction and Faraday’s Law An induced emf is always in a direction that opposes the original change in flux that caused it. 3. Lenz’s Law discussion 1) Lenz’s law is consistent with the law of conservation of energy. 楞次定律 闭合的导线回路中所出现的感应电流， 总是使它自己所激发的磁场反抗任何引发电磁感应的 原因. 楞次定律是能量守恒定律的一种表现