1. OS-4 Diffraction and Interference Chapter 31

2. Review from OS 3 Superposition-The adding of waves Constructive interference-Two crests meet or 2 troughs meet – Increase in amplitude – Anti-nodal – Produces bright bands of light Destructive interference-A crest meets a trough – Decrease amplitude or cancellation (NO amplitude) – Nodal – Produces dark bands of light

3. Antinodal and Nodal Antinodal line-Antinodes line up and form a line – Constructive interference Nodal line-Nodes line up to form a line – Destructive interference

4. Review Cont. Frequency-How OFTEN waves pass a point (waves/sec) Wavelength-The length of one complete crest and trough As wavelength increases, frequency decreases (and vice versa)

5. Diffraction Diffraction-The bending of waves around an object or through an opening – Occurs for all waves

6. Diffraction The MOST diffraction takes place when the opening or obstacle is small compared to the wavelength of the wave (ex. Sound passing through a doorway) So a longer wavelength=more diffraction If opening is wide compared to the wavelength, the wave will NOT diffract much (ex. Light)

7. How to increase diffraction Decrease the size of the opening (for single slit/opening) Decrease the distance between openings (for double slit) Longer wavelength (Remember as wavelength increases, frequency decreases)

8. Electromagnetic Waves All electromagnetic waves are the same type but vary according to wavelength.

9. Electromagnetic Spectrum

10. Young’s Experiment 1801-Thomas Young performed Young’s Experiment Greatly strengthened the wave theory of light

11. Young’s Experiment Young passed light through a pinhole The spot on the 2 nd screen was larger than the original opening (showed diffraction) On the 2 nd screen he added 2 small openings close together On the 3 rd screen he saw a series of light and dark regions (an interference pattern-waves overlapping and interfering with each other)

12. Single Slit vs. Double Slit Single slit interference patterns have a wide, bright central band and the side bands are narrower and not as bright Double slit interference patterns-all of the bands are equally spaced and equally bright

13. Simulations for Young’s experiment Colorado site http://www.colorado.edu/physics/2000/schroedinger/two- slit2.html http://www.colorado.edu/physics/2000/schroedinger/two- slit2.html JAVA http://www.ub.edu/javaoptics/applets/YoungEn.htmlhttp://www.ub.edu/javaoptics/applets/YoungEn.html Hawaii http://www.phys.hawaii.edu/~teb/optics/java/slitdiffr/index.h tml http://www.phys.hawaii.edu/~teb/optics/java/slitdiffr/index.h tml Water simulation http://www.acoustics.salford.ac.uk/feschools/waves/diffract3.php http://www.acoustics.salford.ac.uk/feschools/waves/diffract3.php

14. Spectral analysis Another use of diffraction to help identify elements present in charged gases Colorado explained http://www.colorado.edu/physics/2000/quantumzo ne/index.html http://www.colorado.edu/physics/2000/quantumzo ne/index.html Spectral simulation http://phys.educ.ksu.edu/vqm/html/emission.html http://phys.educ.ksu.edu/vqm/html/emission.html Every elements spectral line http://chemistry.bd.psu.edu/jircitano/periodic4.html http://chemistry.bd.psu.edu/jircitano/periodic4.html

15. Hologram Hologram-Interference pattern that is recorded on film Creates a 3-D image when light reflected off an object interferes with incoming light Used in forgery prevention, data storage, licenses, passports, money

16. Hologram Holograms are made using laser light. Why? Laser light is monochromatic and coherent – Monochromatic-one color – Coherent-light having the same frequency, wavelength and phase and traveling in the same direction Normal white light is not monochromatic or coherent!

17. Examples of Diffraction Sound diffracting http://www.acoustics.salford.ac.uk/feschools/ waves/diffract.php#diffraction http://www.acoustics.salford.ac.uk/feschools/ waves/diffract.php#diffraction Various effects (scrool down to radio waves) http://www.acoustics.salford.ac.uk/feschools/ waves/diffract2.php#radiotv http://www.acoustics.salford.ac.uk/feschools/ waves/diffract2.php#radiotv Acoustic room design http://www.acoustics.salford.ac.uk/feschools/ waves/diffract4.php#roomDesign http://www.acoustics.salford.ac.uk/feschools/ waves/diffract4.php#roomDesign

18. MATH Example: Light having a wavelength of 6.2 X 10 -7 meters is projected on a screen. Three bright and three dark bands are observed on a screen 2.0 m away. The 3 pairs of bands measure 4.8 cm. What is the distance between the slits?

19. MATH Required Problems #11 Work on all homework!!!