• Interference of Waves in 2D
Diffraction
• When waves pass through an opening, they
spread out
• When waves pass by an obstacle, they bend
around it
• Larger waves diffract more
• In order to have noticeable diffraction, the
wavelength must be the same or greater than
the size of the opening.
Interference
• When two (or more) waves occupy the same
space, they interfere with each other
• If the waves line up so that their maxima and
minima are aligned, you get constructive
interference
• diagram
• If the waves line up so that their maxima and
minima are opposite, you get destructive
interference
• diagram
2-D Interference
• In two dimensions, the waves from two
sources have to travel different distances to
arrive at a given point.
• At some places we get constructive
interference and at other places, destructive.
• We see this as light and dark bands
• Dark lines of destructive interference are
called Nodal lines
• Bright lines of constructive interference are
called Antinodal lines
• https://www.youtube.com/watch?v=Iuv6hY6z
sd0
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What conditions must exist for all this to be true?
• Sources must have the same frequency
• Sources must be in phase
• Sources must be producing the same wavelength
What would be different if the sources were 180°
out of phase?
Homework:
Worksheet
Page 468 #1-2 or 3
Page 469 # 1-5
Page 484 # 1, 6 (save the rest for tomorrow)
Later: Rest of 469, Rest of 484