Waves Unit Test Review Flashcards
Mechanical Wave
- the transfer of energy thru a material due to vibration
- waves transfer energy not matter
What is a medium?
- the material that waves pass thru
- a medium is the material that permits the transmission of energy thru vibrations
- all vibrations need a medium to transfer waves
What is Net Motion?
the difference between the particles initial and final positions
What makes a medium elastic?
If the medium returns to its original shape after the wave passes through it is said to be elastic.
What is the difference between the transfer of waves thru rigid materials than thru less rigid materials?
- Generally rigid materials transfer waves more efficiently
- Mechanical waves last longer and go faster and farther in rigid materials than in less rigid materials
What are the 2 types of waves?
TRANSVERSE WAVES- a wave in which particles vibrate perpendicular to the flow of energy (water waves, light waves, micro waves, vibrations on instrument strings)
LONGITUDINAL WAVES- a wave in which particles vibrate parallel to the flow of energy (sound waves, ultra sound waves, tsunami waves, earthquake waves)
What causes waves?
Waves are created when a source of energy causes particles to vibrate
How can loudness be increased?
By increasing the amplitude
What is compression?
The region in a longitudinal wave where the medium’s particles are closer together (higher pressure region)
What is rarefaction?
- The region in a longitudinal wave where the medium’s particles are further apart (lower pressure areas)
- the trough on a transverse wave=rarefaction
Crest
the maximum/highest point on a wave
trough
the minimum/lowest point in a wave
Wavelength
the distance between 2 similar points in identical cycles in a wave (ex-from crest to crest or from trough to trough)
amplitude or loudness
the maximum displacement of the wave from its equilibrium point
frequency or pitch
the number of complete cycles that occur in unit time (usually 1sec)
measured in Hz
period (T)
the amount of time for a vibrating particle to complete one cycle
wave speed (V)
the rate at which a wave is travelling thru a medium
What is a phase of a wave
The x-coordinate in transverse and longitudinal waves is called its phase.
Phase shift
the amount that one waveform is displaced along the x-axis from an otherwise identical waveform
What is simple harmonic motion (SHM)?
SHM= any oscillating motion that repeats at regular intervals
What does the speed waves depend on?
-the speed of a wave depends on the density and temp. of a medium
waves travel faster in warmer and denser materials
Linear Density
the mass per unit distance of a string
units are kg/m
what is the range of audible sound waves?
audible sound waves range from 20Hz to 20kHz
infrasonic waves have frequencies below 20Hz
ultrasonic waves have frequencies above 20kHz
What is loudness?
- Loudness describes how humans perceive sound energy
- loundess depends on sound intensity/amplitude
What is the unit to measure sound intensity?
Bel (B) and smaller unit decibel (dB)
normal breathing: 10dB
rock band: 110dB
Speed of sound-where is it fastest?
Sound travels faster in denser and warmer substances, in solids and in hot air
What is the Doppler effect?
when a source of sound approaches an observer, the frequency of the sound increases but when the source of the sound passes the observer the observed frequency decreases
what is interference of waves?
the process of forming a new wave when 2 or more waves meet
what is the principle of superposition
when 2 waves meet the resulting amplitude vector is the vector sum of the amplitudes of the two original waves
constructive interference
the process of creating a wave w/ a larger amplitude when 2 or more waves combine
destructive interference
the process of creating a wave w/ a smaller amplitude when 2 or more waves combine
Standing wave
an interference pattern produced when incoming and reflected waves interfere with each other and create an effect that is a wave pattern that appears to be stationary
node
a node in a standing wave is the location where the particles of the medium are at rest
antinode
an antinode in a standing wave is where the particles of the medium are moving with greatest speed
fundamental frequency or first harmonic wave
a standing wave with 2 nodes on either ends but no nodes in between
this is the simplest standing wave
Beats
beats are formed when frequencies are slightly different
acoustical beats
when sound waves of slightly different frequencies interfere and a periodic change in sound frequency called beats is caused
beat frequency
the frequency of beats produced by the interference of waves with slightly different frequencies
beat frequency is equal to the difference in the frequencies of the interfering waves
FB=F1-F2
Damping
damping is the reduction in the amplitude of a wave
ex because of energy absorption or destructive interference
Resonant frequency
the frequency at which a medium vibrates most easily
Resonance
the condition in which the frequency of the wave is the resonant frequency, amplitude of the wave will be maximum at resonance
examples: earthquake affecting buildings, bridge collapsing, singing causing glass windows to break
what is diffraction
diffraction= spreading out of waves as they pass thru an aperture or bend around objects
diffraction occurs when the size of aperture or obstacle is of same order of magnitude as the wavelength of the incident wave
Example of diffraction
if 2 rooms are connected by an open doorway, sound produced in a corner of one room will be heard in the other room as if it originated in the doorway
when does the amount of diffraction increase?
the amount of diffraction/sharpness of bending increases when wavelength increases and decreases when wavelength decreases
Examples of diffraction
- colours on butterfly wings are due to diffraction of light
- rainbow colours on a CD are due to diffraction
- the reddish appearance of the sun at sunset and sunrise is caused by diffraction
Building acoustics
Building acoustics is the total effect of sound produced in an enclosed or restricted space
- the goal of acoustics is to use echoes to improve sound quality to ensure everyone can hear clearly
- when sound is produced in one part of the room ut spreads out towards the walls where it is reflected or absorbed
Reverberation time
reverberation time is the time it takes for sound to drop by 60dB from its max loudness or to drop down an inaudible level
What affects reverberation time?
Reverberation time can be changed by changing the texture or materials of the wall, ceiling, floor coverings or furniture.
Curved surfaced reflect sound non uniformly, therefore flat surfaces are better to avoid this issue
Human ear and sound
the audible hearing range of a healthy young adult is 20Hz-20kHz
The auditory canal magnifies sounds by a factor of 10 and as result most sound we perceive is in the frequency range of 1000Hz-5500Hz
Music vs Noise
- a musical note originates from a source that vibrates uniformly and with constant frequencies
- noise originates from a source that vibrates in non-uniform, random manners and does not have constant frequencies
Pitch and loudness
- pitch increases when frequency increases
- loudness increases when amplitude of sound wave increases
