Waves
disturbances
(but in a good way! Mostly )
Definition
Waves are
disturbances that
transfer energy!
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Types of Waves
Mechanical Waves
Electromagnetic Waves
• A mechanical wave is a
disturbance that propagates
through a medium.
• A medium is any material
(matter) through which a
wave travels.
• An electromagnetic wave is
simply light of a visible or
invisible wavelength.
• Oscillating intertwined
electric and magnetic fields
comprise light.
• Light can travel without a
medium—super, duper fast.
Mechanical wave examples:
sound; water waves; a pulse
traveling on a spring;
earthquakes; a “people
wave” in a football stadium.
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Types of Mechanical Waves
Longitudinal
Transverse
Particle motion moves
perpendicular to the direction
of wave propagation
(wave motion)
Particle motion moves parallel
to wave propagation
(wave motion)
Examples:
Sound Waves
Seismic waves that travel through the
earth
Examples:
Light waves
Seismic waves that travel on the surface
of the earth
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Types of Waves
Use your slinky to model
longitudinal and transverse
waves
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Wave Characteristics
Wave
Cycle
Wave cycle
Oscillation
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Wave Characteristics
• Amplitude (A) – Maximum displacement
of particle of the medium from its
equilibrium point. The bigger the
amplitude, the more energy the wave
carries.
(In the case of sound Large Amplitude = LOUD)
(In the case of a radio wave
Large Amplitude = great signal strength!)
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Wave Characteristics
Period and frequency
• Period (T) – time required
for 1 complete wave cycle
(measured in seconds).
• Frequency (f) - The
number of cycles passing
by in a given time. The
SI unit for frequency is
the Hertz (Hz), which is
one cycle per second.
T = 1/f
(the number of waves that occur in 1 second)
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Period-Frequency Relationship
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Beach example 
Suppose you were at the
beach and noticed the
waves were hitting your
toes at a regular repeating
interval. You counted 5
waves touching your toes in
10 seconds time.
(Tip: Use your definitions!)
• Determine the
frequency of the waves.
• Calculate the period of
the waves.
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Wave Characteristics
• Wavelength () – Distance from crest (max positive
displacement) to crest, measured in meters.
• Frequency (f) – The number of cycles passing by
in a given time. The SI unit for frequency is the
Hertz (Hz), which is one cycle per second.
• Wave speed (v) – How fast the wave is moving
(the disturbance itself, not how fast the individual particles
are moving, which constantly varies).
The speed of all waves depends on the medium.
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Wave Relationships
Wave-Speed
• Wavelength (λ)
• Frequency (f)
• Propagation speed (v)
v = λf
Example: Sound
The speed of sound at 25 °C
(about room temperature) is 346.13
m/s. Assume you are playing
the piano and strike middle C
(frequency 261.6 Hz).
Rearrange this equation to solve • Calculate the wavelength of
middle C.
for wavelength.
• Determine the period of this
sound wave.
λ = v/f
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Electric Charges
The atom
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Electric field lines
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Electromagnetic Waves
Are made by vibrating electric charges and can
travel through space by transferring energy
between vibrating electric and magnetic
fields.
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E field simulation
Check out this simulation on electric fields
https://phet.colorado.edu/en/simulation/charges-and-fields
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Electromagnetic Waves
Are made by vibrating electric charges and can
travel through space by transferring energy
between vibrating electric and magnetic
fields.
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EM Transmission
Check out these simulations to relate electric fields to
how your CricketSat works.
• http://www.cabrillo.edu/~jmccullough/Applets/Flash/Optics/
EMWave.swf (this one runs automatically)
• https://phet.colorado.edu/en/simulation/radio-waves
(this one you control)
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Speed of Light (c)
c = 3 x 108 m/s
Example:
Suppose your partner were
on the moon and you were
able to make a cell phone
call directly to the moon.
How long would it take the
signal to make it from your
phone on Earth to your
partners phone on the
Moon?
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Your CricketSat
•
Calculate the
wavelength of the
radio wave that your
433 MHz transmitter is
transmitting.
• Assuming that your
CricketSat makes it to 5
km in altitude –
determine the time
required for the 433
MHz signal to reach
your ground station.
M = Mega = 106 = 1 million
k = kilo = 103 = 1 thousand
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EM Spectrum
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Atmospheric Opacity
Where do the radio waves transmitted by our radio fall into this picture?
Do we need to worry about atmospheric absorption?
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The Visible Portion
EM Spectrum
Make a statement about the percentage of
visible light in the entire EM Spectrum
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Frequency allocation chart
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