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Waves
Students will learn about waves
Waves
• Waves transfer energy without the transfer of
mass.
• A wave is a vibratory disturbance that is
transmitted through a material or through
space.
Mechanical Waves
• Mechanical waves require a material medium for
transmission. The energy disturbance is
propagated by the molecules of water, air, or a
spring.
– Transverse waves exhibit simple harmonic motion
about a rest position perpendicular to the direction of
motion. (EX: waves on a string)
– Longitudinal waves exhibit SHM parallel to the
direction of motion (EX: sound, slinky)
– Surface wave exhibit motion both parallel and
perpendicular to the direction (EX water waves)
Electromagnetic Waves
• Electromagnetic waves do NOT need a
material medium for transmission. They can
travel in a vacuum. (EX: light)
Period
• The time it takes for a wave to repeat itself
• Measured in seconds
Frequency
• Number of waves per second
• Frequency is the inverse of period
• Measured in Hertz (older measurements in
1/second or second^(-1))
Amplitude
• Amplitude is the maximum displacement of any
particle in the medium relative to its rest position.
– In a transverse wave the maximum upward displacement is
the “crest” and the minimum downward displacement is
the “trough”
– In longitudinal waves the particles produce region of
maximum compression called condensations and
minimum compression called rarefactions.
– Amplitude is related to the energy carried by the wave.
– Amplitude in sound is Loudness; in light it is brightness.
Wavelength
• The distance between two successive points
on a periodic wave is the wavelength.
• Wavelength is measured in meters.
• Wavelength is symbolized by the Greek letter
lambda.
Speed of a wave
• Speed = wavelength x frequency (m/s)
• Wavelength = speed/frequency
Example
• What is the wavelength of a sound wave
whose speed is 330 m/s and whose frequency
if 990 Hertz?
• Speed = wavelength x frequency
• Wavelength = speed/frequency
•
= 330 m/s/990 = 0.33 m
Speed of light
• All electromagnetic waves travel in space at
the speed of light, c, equal to 3 x 10^8 m/s
• (Einstein showed that nothing can exceed the
speed of light, c = 3 x 10^8 m/s)