Diffraction
Download as PPT, PDF4 likes2,200 views
The document discusses the principles and applications of diffraction. It defines diffraction as how waves spread out when passing through an aperture. The amount of diffraction depends on the ratio of the wavelength to the aperture width. A single slit produces a diffraction pattern of bright and dark fringes. Multiple slits produce an interference pattern as each slit acts as a point source. Diffraction gratings can be used to accurately measure wavelengths and produce spectra by separating wavelengths. Applications include measuring unknown wavelengths, identifying materials through their spectra, and determining the composition of stars and nebulae.
Diffraction
- 1. diffraction
- 2. Definitions Single slit diffraction Multiple slits Diffraction grating Applications
- 3. Definition Diffraction = waves spread out as pass aperture e.g. sound water radio waves Amount diffraction depends on ratio of to aperture width, a
- 4. Diffraction of light - single slit light 400 – 700 nm V. small slit needed! Huygen’s principle – predicts future position of wavefront each point on wavefront is a point sources of wavelets Wavelets superpose + interfere to form future wavefronts
- 6. Diffraction pattern = series of bright and dark fringes Central maximum Secondary maxima
- 7. Red filter used … More diffraction if increased Aperture width decreased What would pattern look like if blue filter used?
- 8. Diffraction - multiple slits Effects similar to Young's interference pattern As number slits increases, maxima = brighter + sharper Each slit acts as point source of 2 ° wavelets individual diffraction patterns interference Superposition of single slit pattern on multiple patterns
- 10. Diffraction grating Transmission grating Reflection grating Use: produce spectra to measure accurately 2 nd order 1 st order Zero order 1 st order 2 nd order Laser
- 11. Coarse/fine grating Increasing coarseness = increasing number of orders (and orders closer together)
- 12. Theory
- 13. Angle is such that wave B in phase with wave A path difference is for 1 st order principle maxima 2 for 2 nd order 3 for 3 rd order n for n th order
- 14. ABC: Sin = AC = AC = n AB d d Or n = d Sin
- 15. Spectrometer Collimator parallel light diffraction grating Pattern observed measured find
- 16. Applications Accurate method of measuring Can separate s close together Identify v. small quantities of material since different elements = different spectra Analysis of light from stars, nebulae and interstellar gas determine of structure