Celtic Harp
Irish folk tunes
arranged by
Howard Baer
Propagation of
Waves
Key Terms
HReflection
HRefraction
HAbsorption
Diffraction
Diffraction is
significant only when
D≤λ
Interference
HInterference
occurs
whenever two waves
occupy the same space
at the same time.
Resultant Wave
HThe
combined wave
formed by the superposition of two individual waves
Constructive Interference
HThe
two interfering waves
reinforce one another
HOccurs
when the two waves
are in phase
Constructive Interference
Destructive Interference
Destructive Interference
HThe
two interfering waves
cancel one another
HOccurs
when the two waves
are out of phase
Video I-3
Interference: Transverse
Waves on a String.
Constructive Interference –
Waves
2
1.5
1
0.5
0
-0.5
-1
-1.5
-2
Destructive Interference –
Waves
1
0.5
0
-0.5
-1
Constructive Interference
(unequal amplitudes)
2
1.5
1
0.5
0
-0.5
-1
-1.5
-2
Destructive Interference
(unequal amplitudes)
1
0.5
0
-0.5
-1
Sound From Two Sources
Sound From Two Sources
HConstructive
interference
occurs when
L1 - L2 = n λ
Sound From Two Sources
HDestructive
interference
occurs when
L1 - L2 = (n+ ½)λ
Video II-5
Interference of Sound Waves
Beats
HOccur
when two waves of
slightly different
frequency interfere
Beats
1
0.5
0
-0 . 5
-1
2.5
2
1.5
1
0.5
0
-0 .5
-1
-1 .5
-2
Video II-6
Beats
Beat Frequency
fbeat = |f1 -f2|