[工学]大学物理双语版奥本汉姆课件Chap27To29-EMagIndu---.ppt

* Chapter 27 to 29 Electro-Magnetic Induction and Field The Law of Electro-Magnetic Induction Motional(动生) Induced(感生) EMF Self and Mutual Induction(自感与互感) Energy Stored in a Magnetic Field Displacement Current Ampere-Max’ Law Maxwell’s Equation 27-1. Electro-Magnetic Induction’Law After Oersted’s discovery in 1820: a steady current produced a steady magnetic field. Experimentalists eagerly sought to demonstrate the reverse: a steady magnetic field could create a steady electric current. Michael Faraday (1791-1867), English physicist and chemist, whose experiments covered a wide range of electrical, magnetic, optical and chemical phenomena. He is best known for his famous discovery of electro-magnetic induction. 1. Faraday’s law of induction (P630) Common points: Flux of changes and electromotive force (EMF) (电动势)occurs. The magnitude of the EMF induced (感应电动势)in a conducting loop is equal to the rate at which the through that loop changes with time. where is magnetic flux through area A. voltage (V). (Faraday’s law) For a coil of N turns (the coil is closely packed, the same magnetic flux passes through all the turns, the total EMF induced in the coil is: (coil of N turns) SI unit: 1 weber = 1Wb = 1T · m2 The steps to determine the direction of i by Faraday’s law: (1) Freely set a positive normal direction of a loop ; (2) If (3) If L L (1) If the loop’s resistance is R, then induced current in the loop is: (2) The charges in the loop (通过回路的电量)is: The charges q is directly proportional to ?? and independent on d? /dt . Explanations: (Heinrich Friedrich Emil Lenz, a German physicist, in 1834 he proposed this law.) An induced current has a direction such that the magnetic field due to the current opposes the change in the magnetic flux that induces the current (感应电流的方向总是使它产生的磁场去阻碍引起感应电流的磁通量的变化). original Self-loop’ magnetic flux opposing 2. Lenz’s law ?? determin