Maxwell.ppt

1、Chapters 32-33,Maxwells Equations & Electromagnetic Waves,Gauss Law for Magnetic Fields,Gauss law for magnetic field saying that magnetic monopole do not exist. 不存在磁单极,Induced magnetic field,Faradays law of induction shows that the change of magnetic flux (magnetic field) can produce electric field.

2、,Can a changing electric flux (electric field) can induce magnetic field?,Maxwell introduce the displacement current , which can also produce magnetic field.,?,Amperes law:,Since S1 and S2 have the same boundary L, the loop integrals will equal to each other,Displacement Current,Electric Displacemen

3、t Vector,Ampere-Maxwell Law：,Both the conductive current and the displacement current can induce magnetic field.,位移电流（磁场的变化）与传导电流均能激发磁场。,Maxwells equations,Maxwells equations are fundamental laws of the electromagnetic fields.,Electromagnetic Waves,Based on the above equations, Maxwell showed that t

4、he a beam of light is a traveling wave of electric and magnetic fields the electromagnetic wave.,All the laws of optics, such as reflection refraction, total reflection, and Brewsters law can be obtained from the Maxwells equations. (Classical Electrodynamics),Inspired by Maxwells work, Hertz discov

5、ered the electromagnetic wave in laboratory.,The traveling electromagnetic wave,The electric and magnetic fields are always perpendicular to the direction in which the wave is traveling. The wave is transverse wave.,(2) The electric field is always perpendicular to the magnetic field.,(3) The cross

6、product always gives the direction in which the wave travels.,(4) The fields always vary sinusoidally, and the fields vary with the same frequency and in phase with each other.,电场与磁场同频率，同相位,(5) The amplitude of the electric field is proportional to that of the magnetic field,(6) The wave speed is a

7、constant.,By combing (5) and (6), we can obtain,坡印亭矢量,Energy Transport and the Poynting Vector,Energy density,Energy current density,Polarization (偏振),The plane containing the electric field is called the plane of oscillation. The electric field vector is called the optical vector.,由于电场与人的眼睛及光学器件之间的

8、相互作用强度比磁场大得多，在光学中电场矢量称为光矢量。,The (completely) polarized light (完全) 偏振光 Unpolarized light (完全）非偏振光 Partially polarized light 部分偏振光,To represent the polarization, we view the plane of oscillation head-on and indicate the directions of the electric field with a double arrow.,The polarization states of l

9、ight:,Polarized light:,Unpolarized light:,The light emitted by any comment source are polarized randomly or unpolarized.,普通光源如太阳，灯泡，蜡烛等发出的光，是由大量原子自发辐射产生的，光的偏振方向各不相同，但机会均等。,Partially polarized light:,非偏振光可分解为两个垂直的、振幅相等的独立 (相位差任意) 光振动。,Polarizing sheet (偏振片),We can transform unpoparized and partially

10、polarized light into polarized light by seending it through a polarizing sheet.,Polarizing direction,Intensity of transmitted polarized light,The intensity of the transmitted polarized light is half the intensity of the original unpolarized light.,The decomposition of the electric field of polarized light,R