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Lecture Physics A2: Diffraction - PhD. Pham Tan Thi

Lecture Physics A2: Diffraction - PhD. Pham Tan Thi present the content properties of light, effects of materials on light, definition of diffraction, diffraction of light, diffraction and Hyugen’s principle, Fresnel’s diffraction, . | Diffraction Pham Tan Thi Ph.D. Department of Biomedical Engineering Faculty of Applied Science Ho Chi Minh University of Technology Properties of Light Effects of Materials on Light Transmission Reflection Refraction Absorption Total Internal Reflection Interference Diffraction Scattering of Light Polarization Effects of Materials on Light Materials can be classified based on how it responds to light incident on them 1. Opaque materials - absorb light do not let light to pass through 2. Transparent materials - allow light to easily pass through them 3. Translucent materials - allow light to pass through but distort the light during the passage Definition of Diffraction Diffraction is a bending of light around the edges corners of an obstacle and subsequently spreading out in the region of geometrical shadow of an obstacle. Diffraction of Light When a narrow opaque aperture is placed between a source of light and a screen light bends around the corners of the aperture. This encroachment of light is called diffraction . For diffraction the size of the aperture is small comparable to the wavelength . As a result of diffraction the edges of the shadow or illuminated region are not sharp but the intensity is distributed in a certain way depending on the nature of the aperture. Difference between Interference and Diffraction Interference occurs between waves starting from two or more but finite numbers of coherent sources. Diffraction occurs between secondary wavelets starting from the different points infinite numbers of the same waves. Both are superposition effects and often both are present simultaneously e.g. Young s double slit experiment . Comparison a In an interference pattern the minima are usually almost perfectly dark while in a diffraction pattern they are not so. b In an interference pattern all the maxima are of same intensity but not in the diffraction pattern. c The interference fringes are usually equally spaced. The diffraction fringes are never equally spaced. .