1
Lecture 38
Review of waves
What is a wave ?
Examples:
–
Sound waves (air moves back & forth)
A wave is a traveling disturbance that
transports energy but not matter.
–
Stadium waves (people move up & down)
–
Water waves (water moves up & down)
–
Light waves (what moves??)
Waves exist as excitations of a (more or less)
elastic medium.
Amplitude:
The maximum displacement
A
of a point on the wave.
Period:
The time
T
for a point on the wave to undergo one complete
oscillation.
A few parameters
1
f
T
Frequency:
Number of oscillations
f
for a point on
the wave in one unit of time
Amplitude
A
A
x
y
the wave in one unit of time.
Angular frequency:
radians
ω
for a point on the
wave in one unit of time.
2
f
y
Wavelength:
The distance
λ
between identical points on the wave.
Connecting all these simple harmonic motions
k
2
Wave number
k
:
x
Speed
:
The wave moves one wavelength
λ
in one period
T
, so its
speed is
v
T
f
k
λ
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2
Interference, superposition
Q:
What happens when two waves
“
collide?
”
A:
They ADD together!
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 Spring '07
 Johnson
 Physics, Energy, Light, Cos, huygens, identical harmonic waves

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