2. Waves: Part II Interactions of Waves & Matter S.HS.2B.3.2

3. Interference Interference occurs when waves collide with each other In this diagram, the result is shown in green

5. Interference CONSTRUCTIVE interference happens when the peaks of the waves add together to make a bigger peak, or the troughs add together to make a bigger trough DESTRUCTIVE interference happens when the peak of one wave cancels out the trough of the other

6. Examples of Interference - Light ABOVE: This microscopic view is of the meteorite D'Orbigny. Light gray and white mineral grains are plagioclase feldspar, blue grains are olivine, and red, greenish and tanish ones are pyroxene. The colors are caused by interference of light waves due to viewing a thin (35 micrometers) slice of the meteorite in polarized light. As for eucrites, the shapes of the individual crystals and the way in which they are intergrown indicates that the rock crystallized in a lava flow. http://www.psrd.hawaii.edu/April03/asteroidalLava.html

7. Examples of Interference - Light

8. Please make sure your speakers are ON and the volume is UP before proceeding...

9. Examples of Interference - Sound This sound is an “A” – frequency = 440 cycles/second, or 440 Hz (Click to start) This sound is a slightly sharp “A” – frequency = 442 Hz (Click to start) This sound is what happens when the two frequencies are played together. (Click to start) Those “beats” you hear (the WAH WAH WAH) are the result of the two waves interfering. You hear 2 beats each second because 442 Hz – 440 Hz = 2 Hz. Are these two pitches closer to each other than the example, or farther away from each other?

10. Examples of Interference - Sound This sound is an “A” – frequency = 440 cycles/second, or 440 Hz (Click to start) This sound is a slightly sharp “A” – frequency = 442 Hz (Click to start) This sound is what happens when the two frequencies are played together. (Click to start) Those “beats” you hear (the WAH WAH WAH) are the result of the two waves interfering. You hear 2 beats each second because 442 Hz – 440 Hz = 2 Hz. Are these two pitches closer to each other than the example, or farther away from each other? Answer: Farther away – you can hear faster beats, so the difference between the pitches is greater (here, 500 Hz & 512 Hz)

11. Diffraction Occurs when a wave bends around an object in its path

12. Diffraction & DNA This picture of DNA was made by bending – diffracting – x-rays. Rosalind Franklin took this picture. A-DNA & B-DNA were later found to be just DNA that changed shape by a tiny bit according to the humidity in the lab.

13. Diffraction & DNA This sketch shows how the diffraction pattern seen in the lab relates to the actual shapes of molecules.

14. A reflected wave bounces off an object at the same object it hit; “The angle of incidence is equal to the angle of reflection”

15. Refraction Refraction occurs when a wave changes speed because it’s traveling through a different material. As a result, the wave changes its direction as it travels through the material.

16. Refraction Think of marching soldiers who encounter mud.

17. Refraction: Examples

21. Refracting: Angle of bend depends on color (wavelength) of light

22. Doppler Effect – OnlineOnline To finish... Go here to review with Hangman and complete your worksheet.here