2-04-惠更斯原理.ppt

* 第2章 机械波 2.3.4 惠更斯原理 波的衍射、反射和折射 * When wave passes through some obstacle ,the distribution of wave energy is not clear, there is not a line of boundary. This phenomenon is diffraction of wave. 3. Diffraction of waves and Huygens’ principle Diffraction is the bending of waves as they pass by some objects or through an aperture Diffraction refers to the deviation of wave from straight-line propagation.Its usually corresponds to the bending or spread of wave around the edges of apertures and Obstacles. 波的衍射 水波通过狭缝后的衍射 3. Diffraction of waves and Huygens’ principle 3. Diffraction of waves and Huygens’ principle R1 R2 S1 S2 O Huygens’ principle 3. Diffraction of waves and Huygens’ principle Every unobstructed point on a wavefront will act a source of secondary spherical waves. The new wavefront is the surface tangent to all the secondary spherical waves. 球 面 波 平 面 波 介质中波动传播到的各点都可以看作是发射子波的波源，而在其后的任意时刻，这些子波的包络就是新的波前. 一 惠更斯原理 O . . . . . . . . . . . . . . . . Point source t Δ + t wavefront t wavefront t u Δ 3. Diffraction of waves and Huygens’ principle All points on a wavefront can be considered as point sources for producing spherical secondary wavelets. After a time Δt ,the new position of the wavefront will be the surface of tangency to those secondary wavelets. barrier . . . . . . . . . Plane wave Plane wavefront Wavefront Wave ray 3. Diffraction of waves and Huygens’ principle Explanation to diffraction with huygens’ principle 波的衍射 水波通过狭缝后的衍射 波在传播过程中遇到障碍物时，能绕过障碍物的边缘，在障碍物的阴影区内继续传播. 二 波的衍射