Diffraction

Diffraction is the spreading of waves in to a region that are hidden behind an obstacle or gap

http://ngsir.netfirms.com/englishhtm/Diffraction.htm

In General you should find that if a wave passes through a gap in an obstacle where the size of the gap is close to the wavelength, the diffraction will be strong. If the wave passes through a gap that is much bigger or smaller than the wavelength then the effects will be minimal.

http://physics.info/diffraction/

1. In our everyday environment, diffraction is much more evident for sound waves than for light waves. Why is this so? Describe a situation that could be used to verify this claim.
2. Why are TV broadcasts in the VHF range more easily received in areas of marginal reception than broadcasts in the UHF range? Remember, UHF frequencies are higher than VHF frequencies. (Assume that both types of frequencies are broadcast under identical conditions.)
3. A calculation and a related question.
   1. Verify the claim that a 2500 Hz sound wave in air has a wavelength approximately equal to the width of a typical adult human head.
   2. What is the significance of this value? That is, what kind of perceptual difference might there be between sounds above 2500 Hz and sounds below 2500 Hz? (Hint: Typical humans have two working ears.)
4. The door on a microwave oven is basically a double layer of safety glass with a perforated metal foil layer in between. The perforations allow you to see the food inside while at the same time keeping the microwaves trapped inside. How is this possible? Why is it that the light can escape the oven, but the microwaves can't?

http://physics.info/diffraction/problems.shtml

Some really cool examples of diffraction from google earth!!!!

http://xxx.lanl.gov/pdf/1201.0001v1.pdf

Green Laser Diffraction

http://www.nationalstemcentre.org.uk/elibrary/resource/2081/diffraction-of-laser-light