Wave Interference
PHYS/MUS 102, SPRING 2015
Longitudinal drawn as Transverse Waves
2. But it can be represented by drawing our typical sine wave
1. It’s a longitudinal wave
What happens when 2 pulses interfere?
Constructive Interference
Destructive Interference
Wave interference (aka superposition)
What happens when 2 sources with different
frequencies interfere?
Answer: Beats!
fsum =
Questions: Where does occur in a music context, and what will this sound like?
Tune up
Two-source interference
Quantifying intensity maxima
m=2
m=1
Source 1
d
m=0
Source 2
m = -1
L
m = -2
z
Amplitude (arb. units)
Amplitude (arb. units)
Phase shift
Source 1
1.5
1
0.5
0
-0.5
-1
-1.5
0
2
4
6
8
10
12
14
16
18
20
f
x (m)
Source 2
1.5
1
0.5
0
-0.5
-1
-1.5
0
2
4
6
8
10
x (m)
12
14
16
18
20
Predicted (theoretical) locations of
maxima/minima
Maxima occur where:
ml = d sin q = d (z/L)
m = …-2, -1, 0, 1, 2
Minima occur where:
(m+1/2)l = d sin q = d (z/L)
Symphony of Superposition
Image sources
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Boston University
http://sirius.ucsc.edu/demoweb/cgi-bin/?waves-visible-intermodel
http://www.paulfriedlander.com/text/timetravel/experiment.htm
http://web.sbu.edu/chemistry/wier/electrons/young.html
http://hyperphysics.phy-astr.gsu.edu/hbase/sound/beat.html#c2
http://www.animations.physics.unsw.edu.au/waves-sound/interference/
http://www.animations.physics.unsw.edu.au/jw/beats.htm
http://www.phys.unsw.edu.au/jw/uncertainty.html