Lecture 33 Longitudinal and transverse wave, diffraction X-ray crystallography

Transverse Wave Transverse waves are moving waves that consists of oscillations occurring perpendicular (or right angled) to the direction of energy transfer. Examples: wave in a rope, string water wave Electromagnetic wave (E and B)

Longitudinal wave Longitudinal waves are waves in which the displacement of the medium is in the same direction as, or the opposite direction to, the direction of travel of the wave. Examples: Sound, Earthquark

Diffraction Diffraction refers to various phenomena which occur when a wave encounters an obstacle or a slit. In classical physics, the diffraction phenomenon is described as the interference of waves according to the Huygens Fresnel principle.

Huygens–Fresnel principle In 1678, Huygens proposed that every point which a luminous disturbance reaches becomes a source of a spherical wave; the sum of these secondary waves determines the form of the wave at any subsequent time.

Single-slit Diffraction Diffraction of a plane wave when the slit width equals the wavelength

Single-slit Diffraction Diffraction of a plane wave at a slit whose width is several times the wavelength

Optical diffraction

Circular aperture diffraction 第一极小位置 系数1.22为几何形状导致

Electron Diffraction and matter wave de Broglie hypothesis: all matter can exhibit wave-like behavior.

Diffraction grating A diffraction grating is an optical component with a periodic structure, which splits and diffracts light into several beams travelling in different directions

Spectrometer 镉发光的光栅图 氢原子发光的光栅图

X-ray crystallography X-ray crystallography is a tool used for identifying the atomic and molecular structure of a crystal, in which the crystalline atoms cause a beam of incident X-rays to diffract into many specific directions.