Waves, Chapter 20 (PS 8 & 9)
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Section 20-1
Vocabulary
Wave
can be mechanical
or electromagnetic
Medium
Mechanical Wave
(type)
(matter &
medium)= m & m’s
Explanation
Drawing/Example
A disturbance that transmits ENERGY (not matter!)
through SPACE and/or MATTER.
To make the wave travel further, it has to have
more ENERGY. (Think of yelling!)
A SUBSTANCE the wave travels through, such as
SOLIDS, LIQUIDS OR GAS.
The matter DOES NOT move with the wave, just
the ENERGY!
Require a MEDIUM
Particles bump particles to transmit energy
Examples: LIGHT, SOUND, OCEAN
Think about solids/liquid/gas particle
arrangement
Ex: DOMINOES HITTING DOMINOES…
CARRIES ENERGY, BUT NOT THE DOMINO
Examples: SOUND, WATER
EM (ElectroMagnetic) SPECTRUM
Electromagnetic
Wave (type)
Do not require a MEDIUM
Examples: LIGHT WAVES (microwaves,
radio, light, xray)
Transverse
All transverse!
Compression /
Longitudinal
(make graphic
organizer now)
Waves in which particles vibrate with an UP &
DOWN MOTION and the particles move
PERPENDICULAR to the direction the wave is
traveling.
Require a medium? NO
Waves in which particles of the MEDIUM vibrate
BACK & FORTH (particles bump barticles)
along the path the wave travels. (and repeat
pattern)
Require a medium? YES
The HIGHEST point of a TRANSVERSE wave
Crest
The LOWEST point of a TRANSVERSE wave
Trough
Compression
The area where the PARTICLES of the wave
CROWD TOGETHER for a COMPRESSION
(longitudinal) wave
Rarefaction
The area of where the PARTICLES of the wave
SPREAD APART for a COMPRESSION (longitudinal)
wave
(label wave
diagrams now)
Examples: EM WAVES
Examples: SOUND
Section 20-1 Review
A wave is a DISTURBANCE that carries ENRGY. A wave can travel through MATTER or SPACE. There
are two kinds of waves we’ve discussed: waves that require a medium called MECHANICAL or
waves that do not require a medium called ELECTROMAGNETIC. The TRANSVERSE waves have
crests and troughs and are the ELECTROMAGNETIC waves. The COMPRESSION (or
LONGITUDINAL) waves have compressions and rarefactions are the MECHANICAL waves.
Section 20-2
Vocabulary
Explanation
Wave
Velocity/Speed (v)
Measured in m/s.
Velocity depends on the MEDIUM for a compression
wave.
Frequency
(f)
Hertz (Hz)
Wavelength
(λ)
Unit: meters
Amplitude
(m)
Drawing/Example
V = λ x f (put in triangle w/ units)
Think of velocity due to medium…
The number of WAVES produced in a given amount
of TIME (how many WAVES pass each SECOND)
Count the number of CRESTS or TROUGHS for a
transverse wave or the number of COMPRESSIONS
or RAREFACTIONS for a compression/longitudinal
wave that pass by each second.
The higher the frequency, the SHORTER the
wavelength and the ( less / more ) energy.
The unit used to measure FREQUENCY:
1 Hz = 1 WAVE/SECOND
The DISTANCE between two adjacent CRESTS or
TROUGHS for a transverse wave or the distance
between two adjacent COMPRESSIONS or
RAREFACTIONS for a compression/longitudinal wave
λ and f have INVERSE relationship
The MAXIMUM distance a wave vibrates from the
REST POSITION (also called equilibrium).
(1/2 the “height” of the wave)
The larger the amplitude, the ( less / more ) energy.
bottom pic has most energy due to highest
amplitude
Section 20-2 Review
There are four properties of waves: wave velocity measured by m/s, frequency measured in HERTZ (Hz), wavelength
measured in METERS and amplitude measured in METERS. The speed of a wave is determined by the MEDIUM the
wave is traveling through. If wavelength increases, frequency DECREASES.
Section 20-3
Vocabulary
Explanation
Reflection
The BOUNCING BACK of a wave after it hits a BARRIER
or an object
Drawing/Example
Example: echo, sonar, ultrasound
Refraction
The BENDING of a wave as it passes at an ANGLE from
one MEDIUM to another due to the difference in
WAVE SPEED (velocity) in the mediums.
Example:
straw in glass
of water
Diffraction
Interference
Constructive
Interference
Destructive
Interference
The BENDING of waves around a BARRIER or through
an OPENING and is determined by the WAVELENGTH
and/or the size of the BARRIER. (= new waves
produced)
The result of two or move waves OVERLAPPING (as a
result of diffraction). 3 Types: CONSTRUCTIVE,
DESTRUCTIVE OR RESONANCE
When one wave OVERLAPS another wave.
This results in (smaller/larger) amplitudes, which
means MORE energy or LOUDER sounds. (or brighter
light)
When one wave OVERLAPS another wave.
This results in (smaller/larger) amplitudes, which
means LESS energy or SOFTER sounds. Or dimmer light
Two waves with identical amplitudes will CANCEL
EACH OTHER. = SILENCE
Resonance
What occurs when an object vibrating at or near the
RESONANT FREQUENCY of a second object causes the
second object to VIBRATE.
(They vibrate at maximum amplitude at certain
frequencies.)
Example: light coming into dark
room from hallway or hearing
sounds from locker area in
classroom
Example: PEOPLE TALKING AT
SAME TIME
Example: band vs soloist
or one candle vs several
Example: sometimes happens in
orchestra halls = dead/silence
spots
Noise cancelling headphones
Example: your car shakes due to
car next to you having thumping
stereo
Or making sound from rubbing
rim of water glass
Section 20-3 Review
There are four wave interactions: REFLECTION, REFRACTION, DIFFRACTION or INTERFERENCE. Seeing myself in the
mirror is an example of REFLECTION and seeing light come into a dark room from a hallway is an example of
DIFFRACTION. When waves overlap and become louder, we call it CONSTRUCTIVE interference. When one object
vibration causes another object to vibrate, we call that RESONANCE.