Waves

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Waves

• Two basic kinds
• Mechanical
• Electromagnetic
• Three types of Mechanical waves by the way they
  travel (propagate).
• Transverse
• Longitudinal
• Torsional

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Mechanical Waves
Waves are a disturbance that travels through some
medium. Ex sound, wave on string, wave in
water, tsunami, earthquake, wave on slinky, etc.
Note that electromagnetic waves (light, x-rays,
etc.) do not require a medium and thus are not
mechanical waves.
Transverse waves have disturbance perpendicular
to the direction of travel.
Longitudinal waves have disturbance parallel to
the direction of travel.
The disturbance propagates with wavespeed v.
We will study wave that are periodic in
particular, we will look at wave where each point
in the medium undergoes SHM (moves sinusoidally
with time.)
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v
P
l wavelength T period time to travel l
distance f frequency 1/T oscillations per
second made by point P undergoing SHM
True for all waves (mechanical and
electromagnetic)
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Waves on the surface of deep water are a
combination of transverse and longitudinal waves.
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Traveling wave pulse
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What is the intensity level in dB of a sound that
is 1000 times the intensity of the threshold of
hearing?
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Superposition of Waves
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Superposition of Waves
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Superposition of sinusoidal waves of various
phase differences
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Formation of Standing Waves
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Motion of a string in the n 2 standing wave
mode.
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Second Harmonic (first overtone)
Normal modes of oscillation of a string.
Third Harmonic (second overtone)
First Harmonic (fundamental)
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Graphs represent displacement amplitudes
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Graphs represent displacement amplitudes
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Normal modes of oscillation for longitudinal
standing waves on a rod. Dashed lines represent
amplitudes parallel to the rod.
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Doppler shift with moving observer
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Doppler shift with moving observer Note that v0
lt v
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Doppler shift with moving source
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Doppler shift with moving source (vs lt v) Note
that the velocity of the wave relative to the air
is unaffected by the motion of the source.
Source Approaching
Source Moving Away
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vs gt v
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Beat Frequency f2 - f1
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Fourier Synthesis