OS4 Diffraction and Interference Chapter 31 Review from

OS-4 Diffraction and Interference Chapter 31

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

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

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)

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

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)

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)

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

Electromagnetic Spectrum

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

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)

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

Simulations for Young’s experiment • Colorado site http: //www. colorado. edu/physics/2000/schroedinger/twoslit 2. html • JAVA http: //www. ub. edu/javaoptics/applets/Young. En. html • Hawaii http: //www. phys. hawaii. edu/~teb/optics/java/slitdiffr/index. html • Water simulation http: //www. acoustics. salford. ac. uk/feschools/waves/diffract 3. php

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 • Spectral simulation http: //phys. educ. ksu. edu/vqm/html/emission. html • Every elements spectral line http: //chemistry. bd. psu. edu/jircitano/periodic 4. html

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

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!

Examples of Diffraction • Sound diffracting 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/diffract 2. php#radiotv • Acoustic room design http: //www. acoustics. salford. ac. uk/feschools/ waves/diffract 4. php#room. Design

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?

MATH • Required Problems #11 • Work on all homework!!!